Euro Control Reference of RASS-S Technical

EUROPEAN ORGANISATION FOR THE SAFETY OFAIR NAVIGATION

EUROCONTROL

EUROPEAN AIR TRAFFIC CONTROL HARMONISATION ANDINTEGRATION PROGRAMME

RADAR SENSORPERFORMANCE

ANALYSIS

SUR.ET1.ST03.1000-STD-01-01

Edition : 0.1Edition Date : June 1997Status : Working DraftClass : EATMP

DOCUMENT IDENTIFICATION SHEET

DOCUMENT DESCRIPTION

Radar SensorPerformance Analysis

EWP DELIVERABLE REFERENCE NUMBER

PROGRAMME REFERENCE INDEX EDITION 0.1:

SUR.ET01.ST01-STD-01 EDITION DATE :June 1997

Abstract

WARNING The present version of the document is working draft. It will bevalidated through the Radar Sensors Appraisal Programme. Theresults of this programme are expected end of 2001. Then thedocument will migrate to a released status. Until then it should beused as a support document for the EUROCONTROL Standarddocument for Radar Surveillance in En-Route Airspace andMajor Terminal Areas.

Keywords

CONTACT PERSON : S. Adamopoulos TEL : 3259 UNIT : SUR

DOCUMENT STATUS AND TYPE

STATUS CATEGORY CLASSIFICATIONWorking Draft þ Executive Task þ General Public þDraft o Specialist Task o EATMP oProposed Issue o Lower Layer Task o Restricted oReleased Issue o

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Radar Sensor Performance Analysis SUR.ET1.ST03.1000-STD-01-01

Edition 0.1 Working Draft Page iiiJune 1997

DOCUMENT APPROVAL

The following table identifies all management authorities who have successively approved thepresent issue of this document.

AUTHORITY NAME AND SIGNATURE DATE

SURT

Chairman

M. Rees

DIS J. Van DOORN

EATMP

Project Leader W. Philipp


Page iv Working Draft Edition 0.1June 1997

DOCUMENT CHANGE RECORD

The following table records the complete history of the successive editions of the presentdocument.

EDITION DATE REASON FOR CHANGESECTIONS

PAGESAFFECTED

(Edition) (Edition date)


Edition 0.1 Working Draft Page vJune 1997

TABLE OF CONTENTS

DOCUMENT IDENTIFICATION SHEET ............................................................................... ii

DOCUMENT APPROVAL ...................................................................................................... iii

DOCUMENT CHANGE RECORD ........................................................................................iv

TABLE OF CONTENTS.........................................................................................................v

FOREWORD............................................................................................................................1

1. INTRODUCTION ................................................................................................................3

1.1 Purpose ..........................................................................................................................3

1.2 Scope ..........................................................................................................................4

2. REFERENCES....................................................................................................................5

3. DEFINITIONS, SYMBOLS AND ABBREVIATIONS.........................................................8

3.1 Definitions.........................................................................................................................8

3.2 Symbols and abbreviations ..........................................................................................23

4. RADAR SENSOR PERFORMANCE ANALYSIS.............................................................25

4.1 General ........................................................................................................................25

4.2 Analysis method .............................................................................................................26

4.3 Procedure .......................................................................................................................26

4.4 Interpretation of results................................................................................................31

5. PRIMARY SENSOR DETECTION PERFORMANCE PARAMETERS ANALYSIS.......32

5.1 General ........................................................................................................................32

5.2 Probability of target position detection ......................................................................32

5.3 False target reports.......................................................................................................34

6. PRIMARY SENSOR QUALITY PERFORMANCE PARAMETERS ANALYSIS.............35

6.1 General ........................................................................................................................35


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6.2 Positional accuracy. .......................................................................................................35

6.3 Resolution.......................................................................................................................39

7. SECONDARY SENSOR DETECTION PERFORMANCE PARAMETERS ANALYSIS 42

7.1 General. ........................................................................................................................42

7.2 Probability of target position detection. .....................................................................42

7.3 Probability of code detection . .....................................................................................44

7.4 False / Multiple SSR target reports ratio....................................................................46

8. SECONDARY SENSOR QUALITY PERFORMANCE PARAMETERS ANALYSIS......54

8.1 General ........................................................................................................................54

8.2 Positional accuracy. .......................................................................................................54

8.3 False code information..................................................................................................58

8.4 Resolution.......................................................................................................................60

9. PSR/SSR DATA COMBINING ANALYSIS ......................................................................62

9.1 General ........................................................................................................................62

9.2 Data analysis...................................................................................................................62

9.3 Interpretation of results................................................................................................63

10 ON-SITE DELAY ANALYSIS...........................................................................................63

10.1 General ........................................................................................................................63

10.2 Data analysis.................................................................................................................6310.3 Interpretation of results 63

11. AVAILABILITY ANALYSIS...............................................................................................65

11.1 General ........................................................................................................................65

11.2 Data analysis.................................................................................................................67

11.3 Interpretation of results..............................................................................................68

ANNEXES

ANNEX A (RECOMMENDED)RADAR SENSOR TECHNICAL PERFORMANCE ANALYSIS


Edition 0.1 Working Draft Page viiJune 1997

ANNEX B (INFORMATIVE)RADAR SENSOR DETAILED TECHNICAL PERFORMANCE ANALYSIS

ANNEX C (RECOMMENDED)FLIGHT TESTING METHODS

ANNEX D (RECOMMENDED)METHOD TO ASSES THE RESOLUTION CAPABILITIES OF RADAR SENSORS


Edition 0.1 Working Draft Page 1June 1997

FOREWORD

1. Responsible Body

This Standard has been developed and is maintained by the SurveillanceSubgroup on Standards (SSGS).

2. EATCHIP Work Programme Document

This Standard is identified as deliverable O1 in the EATCHIP Work ProgrammeDocument (EWPD), Surveillance Domain, Executive Task O1, Specialist Task03.

3. Approval of the Standard

3.1 This Standard is adopted in accordance with the procedures outlined in theDirectives for EUROCONTROL Standardisation Ref OO2 - 2 - 93.

3.2 This Standard becomes effective upon adoption by the PermanentCommission of EUROCONTROL.

4. Technical Corrigenda and Amendments

This Standard is kept under review by the responsible body who, whenchanges or corrections are necessary, will prepare the required amendmentsor technical corrigenda. The procedure for the maintenance of this Standard islaid down in the Directives for the Uniform Drafting and Presentation ofEUROCONTROL Standard Documents Ref OO 1 - 1 - 92.

5. Editorial Conventions

5.1 The format of this Standard complies with the Directives for the UniformDrafting and Presentation of EUROCONTROL Standard Documents.

5.2 The following practice has been adhered to in order to indicate at a glance thestatus of each statement.

Normative Elements have been printed in light face roman text;

Recommended Elements have been printed in light face italics, the statusbeing indicated by the prefix Recommendation.

5.3 The following editorial practice has been followed in the writing ofspecifications:

for Normative Elements the operative verb “shall” is used; for RecommendedElements the operative verb “should” is used


Page 2 Working Draft Edition 0.1June 1997

5.4 Any information which is essential to the understanding of a particular indentwill be integrated within the text as a note. It will not contain specifications andwill be placed immediately after the indent to which it refers.

6. Relationship to other Standard Documents

This Standard is related to the EUROCONTROL Standard for RadarSurveillance in En-Route Airspace and Major Terminal Areas Ref OO6 - xx.

7. Status of Annexes to This Document

There are four Annexes to this Part of the Standard Document, the status ofeach being defined as follows:• Annex A Recommended;• Annex B Informative;• Annex C Recommended;• Annex D Recommended.

8. Language Used

The underlined version of this Standard Document is in the English language.



1. INTRODUCTION

1.1 Purpose

1.1.1 This document constitutes the EUROCONTROL Standard concerning themethods and procedures for the Radar Sensor Performance Analysis whichwill apply for the verification and maintenance of Radar Surveillance systems inthe frame of EATCHIP.

1.1.2 The comprehensive and continuous radar coverage of high quality andreliability is essential for the uninterrupted provision of radar services and theapplication of specific radar separation standards.

1.1.3 As an integral part of Air Traffic Management, radar positional data constitutethe principal means of Surveillance of Aircraft for the efficient execution of AirTraffic Control.

The EUROCONTROL Standard for Radar Surveillance specifies commoncriteria with the aim of achieving the optimal use of the Surveillance Functionand the harmonised application of radar separation minima, in line with therelevant objectives as contained in the European Civil Aviation Conference(ECAC) En-Route Strategy for the 1990s adopted by Transport Ministers ofECAC States at Paris in April 1990 and in the EATCHIP Work ProgrammeDocument (EWPD) and the EATCHIP Convergence and ImplementationProgramme Document (CIPD). The EUROCONTROL Radar SensorPerformance Analysis Standard specifies methods and procedures foranalysing and maintaining the performance of Radar Sensors in accordancewith the EUROCONTROL Radar Surveillance Standard.

1.1.4 In accordance with the ECAC En-Route Strategy, comprehensive Radarcoverage is to be completed throughout the continental ECAC area by 1996, atthe latest. A common En-Route separation of 5 NM is to be implementedthroughout high density traffic areas. Elsewhere En-Route separation of notmore than 10 NM is to be implemented.

1.1.5 In accordance with ECAC Strategy and its related documents (EWPD andCIPD), a common radar separation standard of 3 NM is to be implemented inmajor terminal areas.



1.2 Scope

1.2.1 This EUROCONTROL Standard specifies the methods and procedures for theperformance analysis of the Radar Sensors used for Air Traffic Management.

1.2.2 The illustration at Figure 1.1 gives an overview of the operational requirementsfor radar data in relation to the services to be provided within the different typesof Airspace and the corresponding technical requirements of the radar system.

1.2.3 The illustration at Figure 1.2 gives a functional overview of the radar chain.These functions can be performed using different system layouts (e.g.integration of the monoradar tracking function in the Plot Filter Combiner).

1.2.4 The methods and procedures for the performance analysis specified withinthis standard are limited to the Radar Sensor. The elements involved in theRadar Sensor are Primary (PSR) and Secondary (SSR) Radar Sensors.

1.2.5 The methods and procedures specified in this standard are not intended toverify exhaustively the performance of the Radar Sensor. Only thoseperformance parameters which are specified in the EUROCONTROL RadarSurveillance Standard are included (ERSS).

1.2.6 Recommended methods and procedures for the technical performanceanalysis of the radar sensor are specified in ANNEX A. Methods andprocedures for the detailed technical performance analysis of the differentelements of the Radar Sensor (i.e. antenna, receiver etc.) are specified inANNEX B (Informative).



Figure 1.1 Relationship between Airspace Types and Services, Operational

Requirements and the Surveillance Equipment.





2. REFERENCES

2.1 The following documents and standards contain provisions which, through reference in this text, constitute provisions of this EUROCONTROL

Standard.

At the time of publication of this EUROCONTROL Standard Document, theeditions indicated for the referenced documents and standards were valid.

Any revision of the referenced ICAO Document shall be immediately taken intoaccount to revise this EUROCONTROL Standard.

Revisions of the other referenced documents shall not form part of theprovisions of this EUROCONTROL Standard until they are formally reviewedand incorporated into this EUROCONTROL Standard Document.

In the case of conflict between the requirements of this EUROCONTROLStandard and the contents of EUROCONTROL Standard for RadarSurveillance the Standard for Radar Surveillance shall takes precedence.

2.2 At the time of publication , the documents listed below are those that arereferenced from within this Eurocontrol Standard :

• EUROCONTROL Standard for Radar Surveillance in En-Route Airspaceand Major Terminal Areas. Edition May, 1996

• ICAO Annex 5 : Units of Measurement to be used in Air and GroundOperations 4th Edition July 1979.

• ICAO Annex 10 : Aeronautical Telecommunications - Volume 1 4th Edition,April 1985.

• ICAO Document 8071 Edition March 1972.



3. DEFINITIONS, SYMBOLS AND ABBREVIATIONS

3.1 Definitions

For the purpose of this EUROCONTROL Standard document, the followingdefinitions shall apply.

Acceptance tests: The radar sensor performance is analysed andcompared to that specified in the contract between the administration and themanufacturer.

Active Reflector:. A device used in Primary Radar systems forgeographical alignment and system performance checking. It generates asignal from a stationary installation with an artificial Doppler shift whichensures that a stationary target will be presented on an ATC screen afterMoving Target Detection (MTD) or Moving Target Indicator (MTI) processing.

Analogue: In radar terms, a signal which has not been converted intodigitally encoded values, usually quantised into discrete time periods. Analoguesignals are to be found at antenna and receiver level in radar systems.

Analogue - to Digital Converter: A device for the conversion of analoguesignals into digital values. Usually operates by sampling the analogue signal atregular time intervals and converting the measured value of the analoguesample to a digitally encoded number.

Antenna (General): In the case of Radar, an electromechanical device forthe concentrating of radio frequency energy into a "beam" of known andpredictable direction. An antenna can be used for the "concentrating" of energytransmitted from or received at the antenna. Typically the beam shape in eitherthe transmit or receive directions shall be very similar (assuming the same orsimilar transmitted and received frequencies and beam polarisation).Theconcentration of radio frequency energy may occur in both the azimuth andelevation planes. Normally, but not always, an air traffic control radar antennais mounted upon a rotating platform such that it can scan a volumetricairspace through 360 deg of azimuth. However, static electronically scannedradar antennas also exist.

Antenna (Large Vertical Aperture (LVA)): An SSR antennacomprised of a two dimensional array of radiating elements. A typical LVAconsists of a number of columns, each consisting of a vertical linear arraydesigned to produce beam shaping in the vertical plane, arranged in ahorizontal linear array to produce between 2° and 3° azimuth beamwidth.

Antenna (Sum and Difference): An antenna which has been electricallysplit into 2 halves. The 2 half antenna outputs are added in phase at one outputport (sum, Σ) and added in anti phase at a second output port (difference, ∆) toproduce output signals which are sensitive to the azimuth angle of arrival of



received signals, enabling an Off Boresigth Angle for the signal source to beobtained.

Antenna (Reflector): In the case of a reflector antenna the beam isproduced by a method analogous to optics. In most cases the "reflector"surface of the antenna (which may be solid metal, "metalized" syntheticmaterials or metal mesh) is illuminated by a radio frequency source (e.g. aradio-frequency "horn" assembly). The dimensions of the reflector antennaboth in the horizontal and vertical plane, together with the characteristics of theilluminating source, determine the shape and magnitude of the radar beamproduced.

Antenna Elevation (Tilt): Angle between the direction of maximum gain ofthe antenna and the tangent to the surface of the earth at the location of theantenna. A distinction is sometimes made between electronic (radio signal)and mechanical tilt, especially for Large Vertical Antennae (LVA) for SSR. Inthis case the mechanical tilt may be zero when the antenna is radiating at itsnominal design value for electronic tilt, which may typically be 3 deg..

Anntenna (Omni-Directional): Antenna with a circular radiation patternin the horizontal plane. In earlier ISLS systems often used for transmitting the

P2 pulse and sometimes also for transmission of the P1 pulse (I2SLS).Modern omni-directional antennae for SSR use, include a "notch" about thepeak of the control pattern.

Availability requirements (ERSS): The availability requirements areexpressed by:

• maximum outage time due to any given failure;

• cumulative outage time due to all failures over a period of one year;

• outage time due to scheduled actions.

Azimuth: The angle between North (normally true North) and a radartarget, measured from the sensor site.

Azimuth Count (or change) Pulses (ACPs): The output pulses of theincremental azimuth measuring device fitted to the radar antenna turningplatform (turning gear). The encoding device may give its output in serial orparallel form, but typically provides 4096 pulses (12 bit encoding), 16384 pulses (14 bit encoding) or 65 536 pulses (16 bit encoding) in serial formper 360° of azimuth rotation.

Azimuth Extension (Run length, delta theta): The azimuth increment,often expressed as a number of ACPs, from detection of the leading edge of aradar plot to detection of the trailing edge of that plot, in a digital plot extractorsystem.



Back Lobe: A lobe of radiated energy to the rear of an antenna (180° inazimuth with respect to the main lobe).

Beam Width: The angle subtended (either in azimuth or elevation) at the half-power points (3 dB below maximum) of the main beam of an antenna.

Boresight: The main lobe electrical (radio) axis of an antenna.

Cancellation Ratio: The clutter to noise ratio at the output of a processordivided by the clutter to noise ratio at the input of a processor. The processormay be MTI, MTD or ASP. The cancellation ratio is averaged over all targetspeeds.

Chaining: A process of linking together radar target reports (plots andtracks) and other information relating to one particular object.

Clutter: A general term used for interfering reflections of radio energy inPSR. There can be a number of different types of clutter:

• ground clutter (generally non-moving);

• weather clutter (rain, snow, etc.);

• sea clutter;

• angel clutter (slow moving flocks of birds and anomalous propagationconditions).

Code: A combination of data bits contained in signals transmitted by an SSRTransponder in reply to an SSR Interrogator.

Code Train: The sequence of bracket (framing) and code pulses inan SSR Mode A or Mode C reply.

Co-located: An expression used for antennas which are at the samephysical location, but may be on-mounted, back-to-back mounted, etc., andmay use a common turning gear.

Combination Criteria: The criteria with respect to azimuth and rangecoincidence which a primary radar plot and an SSR plot must meet to beconsidered to have come from the same aircraft and therefore to be able to becombined.

Commissioning: The radar sensor performance is analysed in order todefine the airspace volume where the radar sensor can provide radar servicesaccording to local operational requirements.

Combined target report: A target report detected by both PSR and SSRand such that both detections were sufficiently adjacent to be combined intoone target report.



Control Antenna: An SSR antenna has a polar diagram which is designedto "cover" the sidelobes of the main interrogating antenna. It is used to radiate acontrol pulse which, if it exceeds in amplitude the associated interrogationsignal at the input to the transponder, will cause the transponder to inhibitresponses to the interrogation pulses. Modern SSR antenna have the controlelements built into the main array. The control antenna is also known as theSLS (Sidelobe Suppression) antenna.

Control Pattern: This is the polar diagram of the Control Antennadiscussed above. Modern integrated SSR antennae have a "modified cardioid"beamshape.

Control Pulse: A pulse (P2 for Modes A and C, P5 for Mode S),transmitted in accordance with ICAO Annex 10 recommendations, by theground equipment (SSR Interrogator) in order to ensure sidelobe suppressionat transponder level.

Cone of Silence: A gap in coverage above a radar due to the limitations ofthe antenna performance at high elevation angles.

Coverage: Radar Sensor coverage is the three dimensional volume ofAirspace within which the specified performance and availability requirementsare satisfied .

Coverage Measurement Volume (CMV): The coverage measurementvolume is defined as the three dimensional volume of Airspace within whichthe performance and availability requirements will be analysed during aparticular measurement campaign.

Correlated Tracks: Tracks which have been correlated with a flight plan(sometimes this term applies only to tracks for which the Mode A code hasbeen correlated with a Call Sign in the Code/Call-Sign list i.e. Flight PlanAssociation).

Cosecant - Squared Antenna: An antenna pattern for which the gain isproportional to the square of the cosecant of the elevation angle. This results inan approximately constant signal, as a function of range, from an aircraft atconstant flight level.

Dead Time: The period of time during which a SSR transponder is inhibitedfrom receiving signals after a valid interrogation is received and a replytransmitted. The term is also used to describe the time after the normal rangefor returns and before the next transmission of a an interrogator or from aprimary radar system.

Defruiting: A process by which aircraft replies accepted by the Interrogator-Responsor are tested by means of storage and a comparator for synchronismwith the interrogation-repetition frequency. Only replies which are insynchronism (correlate on a repeated basis in range) will be output from thedefruiter. Other replies are rejected as "fruit" or false.



Degarbling: The process of separating (and possibly validating) garbledSSR replies. See also Garbling.

Difference Pattern: The receive (1090 MHz) characteristic of a monopulseSSR antenna, obtained by connecting together in anti phase the signals(replies) received by two partial antennas. The difference pattern has aminimum in the main radiation direction of the antenna, and an amplitude andphase characteristic which varies as a function of angle of arrival of thereceived signal. Used in conjunction with the sum output of the antenna, itenables the off boresight angle to be found.

Doppler Speed: The radial (to the radar sensor) velocity of a target(aircraft) or of a clutter source (false alarm) measured from its Dopplerfrequency shift in a received primary radar return.

Downlink: Associated with signals transmitted on the 1090 MHz replyfrequency channel.

Error: Error is the difference between the measured value (observed) and thereference value (actual)of a physical quantity. The radar errors in position aredivided to:

a) systematic or bias errors which are represented by fixed values:

• ρ slant range bias (at zero range);

• slant range gain ( variation of range bias proportional to range);

• θ azimuth bias.

b) random errors which are represented by standard deviations:

• ρ slant range random error;

• θ azimuth random error.

For the general case the important parameters for a Sensor are the RMSerrors and not the st. dev. . This is since the std. dev. is the RMS error with amean of zero, i.e. the systematic errors are removed.

ERP: Abbreviation for Effective Radiated Power. It is the Transmitted Powerenhanced by the gain of the antenna less the losses of cables, rotary joints etc.

False Plot: A radar plot report (PSR, SSR or combined plot) which doesnot correspond to the actual position of a real aircraft (target), within certainlimits.

Flight Level: The vertical distance above mean sea level when referenced tostandard pressure setting of 1 013.25 hectopascals.



Framing Pulses: The pulses which "frame" the data pulses (code) ofSSR Mode A and C replies (described as F1 and F2 respectively). Also knownas "bracket pulses".

Fringe Envelope: The Fringe envelope is the intersection of the verticalplane passing from the Radar Sensor and the actual coverage. It defines thelimits within which the system satisfies the specified performance andavailability requirements.

Fruit: Unwanted SSR replies received by an interrogator, which have beentriggered by other SSR interrogators. Fruit is the acronym of False RepliesUnsynchronized in Time or False Replies Unsynchronized to InterrogatorTransmission.

Garbling: A term applied to the overlapping in range and/or azimuth of twoor more SSR replies so that the pulse positions of one reply fall close to oroverlap the pulse positions of another reply, thereby making the decoding ofreply data prone to error.

Gain (of Antenna): A measure for the antenna of the increased radiationintensity radiated in a particular direction as compared with the radiationintensity that would have been radiated from an isotropic antenna with thesame power input (expressed in dB).

Hit: A hit denotes the reception by the aircraft equipment (transponder) ofone usable set of interrogation pulses as evidenced by a reply code return, (i.e.receipt of 2 interrogation pulses and 1 control pulse).

Horizontal Polar Diagram (HPD): This is a polar plot of the antenna'sradiation pattern taken in the horizontal plane.

I and Q Channels: The In-phase and Quadrature channels of a MovingTarget Indicator (MTI) or Moving Target Detection (MTD) equipment used forthe extraction of phase and amplitude information of the received signal. Inolder systems these channels were processed separately to avoid “blindphases”.

Improved Interrogation Sidelobe Suppression (I2SLS):A technique whereby interrogation pulse P1 is transmitted via both the main beam and the controlbeam of the SSR antenna, such that a transponder in a sidelobe directionmore reliably receives a P1-P2 pulse pair thus suppressing the reply.

Interlace: A repeating series of SSR interrogation modes. The interlacepattern may be determined either on a p.r.p. (pulse-repetition period) to p.r.p.basis or on an antenna rotation to antenna rotation basis. It may also be madeon a combined p.r.p./antenna basis.



Interleave: The condition where two or more pulse trains becomesuperimposed in time such that their pulse time spacing can be distinguishedand the correct codes established.

Interrogator Repetition Frequency (IRF): See also Pulse RepetitionFrequency; Average number of interrogations per second transmitted by theradar.

Interrogation Side Lobe Suppression (ISLS): A method of preventingtransponder replies to interrogations transmitted through the ground antennasidelobes. The method involves a comparison of the amplitude of the firstinterrogation pulse (P1) of the interrogation with the amplitude of the controlpulse (P2).

Interrogator-Responsor: The ground based combined transmitter-receiverelement of an SSR system.

Leading Edge (Pulse): Front edge of a pulse.

Lobing (Antenna pattern): Due to the process of interference of two waves,one direct and one reflected, differences in phases may cause larger orsmaller amplitudes than expected for free space, causing differences in signalamplitudes measured position of large numbers of dB's. This process is calledlobing.

Mode: The coding of SSR Interrogation transmissions according toICAO Annex 10 recommendations. Modes of interrogation are determined bythe relative spacing of a sequence of transmitted pulses. Mode A and Mode Cinterrogators use the following spacings between the P1-P3 pulse pair:

• Mode 3/A : 8 ± 0.2 microseconds;

• Mode C : 21 ± 0.2 microseconds.

Mode of flight or MOF (General): An aircraft state of motion, characterizedby its Transversal and Longitudinal Accelerations. Examples are Left Turn,Right Turn, Climbing/Descending state, Uniform Motion, etc. MOF’s are usedas input classes in the evaluation system -particularly for accuracy analysis.The classification of Modes-of-Flight (MOF) concerns modes in threedirections transversal modes, longitudinal modes and vertical modes. Withinthese classes the following aircraft motions shall be distinguished:

Transversal modes:

• left expedite turn;

• left standard turn;



• uniform motion;

• slow change of course;

• right expedite turn;

• right standard turn.

ii. Longitudinal modes:

• uniform motion;

• slow speed changes;

• typical and fast speed changes.

iii. Vertical modes:

• altitude hold or slow altitude change;

• typical or fast altitude change.

Figures 3.1. and 3.2. represent the MOF classification in the horizontal andvertical plane -respectively. The duration of a mode of flight segment (i.e. a partof the flight where one particular MOF prevails) depends on the particular MOF.This aspect is not covered in both figures.

Mode of flight (Applicable): For the evaluation of a tracker the following moresimplified subdivision shall be used:

i. Transversal:

a. Constant Course;

b. Intentional Right Turn;

c. Intentional Left Turn.

ii. Longitudinal:

d. Constant Ground Speed;

e. Intentionally Increasing Ground Speed;

f. Intentionally Decreasing Ground Speed.

iii. Vertical:

g. Level Flight;



h. Climb;

i. Descent;

Monopulse: A technique used for determination of the angle of arrival of asingle pulse, or reply within an antenna beamwidth. The angle-of-arrival isdetermined by means of a processor using the replies received through thesum and difference patterns of the antenna. The monopulse technique isgenerally termed "monopulse direction finding" and is a very importanttechnique for SSR in modern ATC.

Moving Target Indicator (MTI): A primary radar filtering device designedto reject fixed clutter and pass moving target on the basis of their Doppler shift.Or more generally a prewhitening filter that reduces the fixed clutter below thewhite noise level..

Moving Target Detector (MTD): A technique for achieving fixed andmoving clutter rejection by a cascade of digital MTI and Pulse Doppler Filters.

Multipath: Interference and distortion due to the presence of more thanone path between transmitter and receiver. See also reflections.

Nautical Mile (NM): A measure used in navigation. The unit is equal to 1852m.

Noise Factor : A figure defined for a receiver as the ratio of the noise atthe output of the practical receiver and the noise output of an ideal receiver atstandard temperature T0 (290° K). The noise factor is in practice defined asthe Signal-to-Noise ratio at the input divided by the Signal-to-Noise ratio at theoutput of a receiver.

North Message: Special message(s) generated by a plot extractor toindicate the passage of the antenna boresight bearing through North.

Object: A combination of radar targets and related information whichare correlated in time and space.

Off Boresight Angle (OBA): In monopulse SSR, the angle (calculatedby the OBA processor) by which a target is off (away from) the boresight (seedefinition), within the beamwidth of the antenna.

On-site processing delay (ERSS): The time expressed in seconds betweenthe moment a radar target for a given aircraft is detected and the momentwhen the corresponding report starts to be transmitted.

Operational Coverage Volume.(OCV): The airspace volume definedduring the site commissioning of the Radar Sensor and in which radarservices can be provided according to the local operational requirements.



Over-Interrogation: Interference in the operation of a secondary radarsystem due to the fact that the number of interrogations exceeds the capacityof the ttransponder (a preset value). The action of the transponder is anautomatic reduction in transponder receiver sensitivity.

Overall (ERSS): When used means that the measurement method shallbe applied without geographical restrictions to the whole sample of therecorded data obtained from opportunity traffic. This sample shall berepresentative of the whole population of aircraft to which air traffic servicesare provided irrespective of radar cross sections and clutter environments forPSR sensors, and irrespective of transponder deficiencies for SSR sensors .

Performance requirements (ERSS): The performance requirementsare divided into detection and quality requirements .

♦ Detection requirements: The detection requirements are expressed bythe:

• target position detection;

• false target reports;

• multiple target reports;

• code detection .

♦ Quality requirements: The quality requirements are expressed by the:

• positional accuracy;

• false code information;

• resolution .

Plot: A target report resulting from digital integration of the received echoes(PSR) or replies (SSR) inside the antenna beamwidth. The PSR reportcontains range and bearing information whereas the SSR report contains inaddition Mode 3/A identity code and the Mode C decoded altimeter height value.

Plot Combiner: A signal processing device for the combination of PSRand SSR data ascertained as having originated from the same target (aircraft).Targets failing to meet pre-defined combination criteria will be output as "PSRonly" or "SSR only" plots in place of "combined plots".

Plot Extractor: A signal processing equipment, which applies digitalintegration techniques to detect and resolve , depending upon design , eitherPSR reflected returns or SSR transponder replies to provide a single messageoutput for each aircraft in the OCV. Both PSR and SSR plot extractors providerange and bearing of the aircraft in the plot output messages whereas SSR



plot extractors also include Mode 3/A identity code and the Mode C decodedaltimeter height value.

Plot Filter: A signal processing device which has the function to filter outradar plot data which can be positively identified as non aircraft returns by ascan-to-scan correlation process.

Plot Run Length: The number of ACPs between the first and lastdetection of a plot presence in a sliding window plot extractor.

Polar Diagrams: Horizontal or vertical radiation diagram for a radarantenna, whereby the relative gain is plotted as a function of the relativeazimuth (Horizontal Polar Diagram, HPD) or as a function of the relativeelevation angle (Vertical Polar Diagram, VPD) generally with respect to themain beam axis).

Polarization: Direction of the electrical field vector of radiated radar energywith respect to a plane tangential to the earth (horizontal, vertical, left-handcircular, right-hand circular, elliptical, etc.).

Polished plots: Target reports at the output of the plot filter whichrejects false targets coming from fruit, reflections, etc. Alternatively they arecalled filtered plots.

Primary Surveillance Radar (PR or PSR): A radar which detectspresence of a target based on reflected radar energy from that target.

Probability of target (position) Detection (Pd): Probability of detection isthe probability that for a given aircraft, at each scan a radar target report withpositional data is produced.

Probability of False Alarm (Pfa): For a long observation period, the actualnumber of detected false alarms divided by the theoretical maximum numberof detections..

Pulse Length: The time between the 50 % amplitude points on theleading and trailing edges of a pulse. Also known as Pulse Width

Pulse Repetition Frequency (p.r.f.): Also known as Pulse RecurrencyFrequency. It is the average number of pulses/interrogations per secondtransmitted by the radar (See Stagger).

Pulse Train: The sequence of framing and code pulses in the coded SSRreply.

Radar Data Processing System (RDPS): A sub-system of an ATC centrewhich processes the incoming radar data (from one or more radar datasources) and prepares it for display.



Radar Cross Section (RCS) : The area intercepting that amount of powerwhich, when scattered equally in all directions, produces an echo at the radarequal to that from the target.

Radial: A straight line of constant azimuth from the radar sensorsite. A radial test flight would follow such a line.

Receiver Side Lobe Suppression (RSLS): A method, usingtwo (or more) receivers to suppress aircraft replies which have been receivedvia sidelobes of the main beam of the antenna.

Reflections: Unwanted signals (PSR or SSR) in the uplink and/or downlinkpaths resulting in erroneous replies entering the data processing system.Typical reflectors are ground obstructions such as aircraft hangars, buildings,towers and adjacent hills or mountains.

Reply: The pulse train received at a SSR ground station as a result ofsuccessful SSR interrogation.

Ring-Around: The continuous reception of aircraft replies tointerrogations by the sidelobes of the ground antenna. This normally occursonly at short ranges and high elevation angles, usually due to the non-existence of a sidelobe suppression mechanism or the improper functioning ofthis mechanism at either the interrogator or the transponder side.

Round Reliability: The probability that when a SSR transmission is madethat a correct reply is received.

Screening: When the shape of the terrain or certain objects prevent thedetection of targets in certain parts of the airspace, one speaks aboutscreening of the parts of the airspace concerned.

Second-Time Around Targets (STAT): Target returns from rangesbeyond that associated with a basic PRF interval.

Sensitivity Time Control (STC): A circuit which controls the gain of aradar receiver, allowing it to rise from an initial preset value to maximum at apredetermined rate to compensate for the decrease in received signal strengthas range increases. This can also be a dynamical threshold operation withfixed gain receivers, such that the threshold below which signals are discardeddecreases with range. Also known as GTC(gain time control).

Sidelobes (Antenna): Lobes of the radiation pattern of an antenna,which are not part of the main or principal beam. Radar systems can havesufficient sensitivity via sidelobes for successful detection of aircraft(particularly for SSR, but also for PSR). Special precautions are necessary toprotect against these false plots.

Sidelobe Suppression (SLS): A mechanism in an SSR transponderactuated by the transmission (radiation) of a Control Pulse (P2 or P5) of



amplitude greater than the antenna sidelobe signals in space, which will enablethe transponder to prevent itself from replying to the sidelobe interrogationsignals.

Split Plot(s): A generation of two plots by a radar extraction systemfor the same target for one passage of the antenna main-beam through thetarget.

Spurious Plots(s): Unwanted radar plot not corresponding directly with anaircraft position (generally applied for SSR).

Stagger (p.r.f.): Deliberate, controlled variation of the p.r.f. of a PSR toovercome blind speeds and decorrelate second time around replies.Deliberate, controlled variation of the p.r.f. of the SSR to prevent aircraft plotsdue to second-time around replies, or synchronous fruit.

Sum Pattern: Normal radiation pattern for the main directional beam ofan antenna. Contrasts with the "difference-pattern", where a part of theradiating elements of the antenna are switched in anti-phase to producesignals proportional to the amount by which the source is off the boresight ofthe sum pattern.

Target report: A digital message which depending on thefiltering function applied can be either polished / filtered plot or track.

Track: A target report resulting from the correlation, by a specialalgorithm (tracking) of a succession of radar reported positions for one aircraft.The report normally contains smoothed position and speed vector information.

Transponder: A unit which transmits a response signal onreceiving an SSR interrogation. The expression is a derivative of the wordstransmitter and responder.

Time stamp: The addition of the time information -in the relevant field-in the target report (plot or track). In the ASTERIX the time information is codedin two octets with Least Significant Bit (LSB) equal to 1/128 seconds.

Time stamp error: Time stamp error is the constant time differencebetween the time system used for plot detection time stamping and a commonreference time.

Validation : The process of determining whether the requirements for asystem or component are complete and correct , the product of eachdevelopment phase fulfil the requirements or conditions imposed by theprevious phase , and the final system or component complies with specifiedrequirements.



Figure 3.1 Horizontal Mode of flight.



Figure 3.2 Vertical Mode of Flight



3.2 Symbols and abbreviations

For the purposes of this EUROCONTROL Standard document, the followingare used:

ACP Azimuth Change Pulse ATC Air Traffic Control ATCC Air Traffic Control Centre ATS Air Traffic Services BITE Built-In Test Equipment CFAR Constant False Alarm Rate CMB Combined (PSR and SSR) CMTP Common Medium-Term Plan CMV Coverage Measurement Volume DGPS Differential Global Positioning System DPE Digital Plot Extractor EATCHIP European Air Traffic Control Harmonization and Integration

Programme EGNOS European Geostationary Orbit System ERP Effective Radiated Power ERSS EUROCONTROL Radar Surveillance Standard FAT Factory Acceptance Tests FRUIT False Replies Unsynchronised In Time GNSS Global Navigation Satellite System GTC Gain Time Control GPS Global Positioning System (US GNSS system) GLONASS Global Navigation Satellite System (CIS GNSS system) HPD Horizontal Polar Diagram ICAO International Civil Aviation Organisation IISLS Improved Interrogation Side Lobe Suppression IF Intermediate Frequency IRF Interrogation Repetition Frequency I/O Input/Output ISLS Interrogation Sidelobe Suppression LVA Large Vertical Aperture MDS Minimum Detectable Signal MOF Mode Of Flight MTD Moving Target Detection MTI Moving Target Indicator MTPA Mobile Transponder Performance Analyser MSSR Monopulse Surveillance Secondary System OCV Operational Coverage Volume OBA Off Boresight Angle PAT Provisional Acceptance Tests Pd Probability of Position Detection Pfa Probability of False Alarm Pcd Probability of Code Detection Pcv Probability of Code Validation PRF Pulse Repetition Frequency



PRI Pulse Repetition Interval PRP Pulse Repetition Period PSR Primary Surveillance Radar (also 'PR') RASS RCS

Radar Analysis Support System Radar Cross Section

RDPS Radar Data Processing System RF Radio Frequency RSLS Receiver Side Lobe Suppression RSS RFM

Radar Separation Standard Remote Field Monitor

RMCS Remote Monitoring and Control System RTQC/A Real Time Quality Control/Assessment SAT Site Acceptance Tests SLS Side Lobe Suppression SPAS SSR

Sensor Performance Analysis Standard Secondary Surveillance Radar

STAT Second Time Around Target STCA STC

Short Term Conflict Alert Sensitivity Time Control

VPD Vertical Polar Diagram VSWR Voltage Standing Wave Ratio



4 RADAR SENSOR PERFORMANCE ANALYSIS

4.1 General

This standard specifies a multilevel approach for the performance analysis ofsurveillance radar sensors (PSR/SSR). The level applied depends on theobjectives of the analysis as follows:

4.1.1 First level: Overall performance analysis

This analysis is to assess the quality of the information, provided by the radarsensor, by measuring the overall performance of the sensor against theperformance parameter reference values specified in the EUROCONTROLSurveillance Standard and this is the objective of this document.

4.1.2 Second level: Technical performance analysis.

This analysis is the in depth evaluation of the radar sensor performance whichshall result either in the definition of the coverage (commissioning) or in theidentification of the reasons of possible performance degradation (ANNEX A).

4.1.3 Third level: Detailed technical performance analysis.

This analysis is the evaluation, of the technical performance, of the individualradar sensor components e.g. antenna, receiver, etc.(ANNEX B).

4.1.4 The first level of testing shall be applied initially upon the completion of thesecond level of testing during system / sensor commissioning leading todefinition of the OCV, and then at regular intervals to ensure that the system/ sensor continues to meet the requirements of the EUROCONTROL RadarSurveillance Standard (Quality Control).

The second level of testing shall be applied initially during commissioning ofthe system / sensor leading to definition of the OCV and then on subsequentoccasions if the first level of testing indicates a failure to meet the statedperformance requirements.

The third level of testing shall be applied in order to supplement the firstand second levels of testing when the system / sensor has been found to befailing to meet the stated performance requirements.

All three levels of testing shall also be applied, as appropriate, and to a suitablelevel , in the following cases:



Overall Technical (ANNEX A) Detailed Technical(ANNEX B)

System System Sub-System F.A.T. C S.A.T. (P.A.T) C C Commissioning C RTQA/Maintenance C C Problem investigation C C C Post modifications C C C

Table 1: Relation of Evaluation Usage to SPAS sections and System

4.2 Analysis method

The Radar Sensor performance analysis shall be based on the computerbased analysis of recorded data at the output of the sensor / input of thecentral radar data processing system. Chaining and trajectory reconstitutionalgorithms shall be applied to the data, in order to evaluate the performanceparameters, of the radar sensor under test.

4.3 Procedure

The procedure for the analysis shall be as follows:

4.3.1 Preparation for the analysis

Before the collection of the data the following shall be done :

4.3.1.1 Definition of the Coverage Measurement Volume

For the overall performance analysis the CMV shall be the OperationalCoverage Volume OCV(defined during site commissioning see ANNEX A ).

4.3.1.2 Recording of the radar sensor status

To facilitate the comparison of the results of different recordings the status ofthe radar sensor during the recording shall be known. The person responsiblefor the analysis shall ensure that at least the radar sensor parameters listedbelow have been recorded and are up to date at the time of the datacollection.Additional system parameters should be traceable through themaintenance records.

4.3.1.2.1 Primary radar sensor (PSR ).

PARAMETERS. UNITS / REMARKS. Antenna tilt Deg. R.P.M Rotations Per Minute (Antenna)

rotations / minute.



P.R.F Pulse repetition Frequency

Hz = 1/ sec.

Staggering ratio/pattern dimensionless/Hz. Instrumented range NM . M.T.I range NM (if applicable). Beam switching azimuth-range pattern. Power KWs-The reading from the power meter of

the radar sensor. Noise figure dB-the reading from the noise figure

indication meter. Receiver sensitivity The relative indication from the equipment's

B.I.T.E., or recent measurement. M.T.D / M.T.I

The indication from the B.I.T.E (internaltests.), or recent measurement.

Plot extractor parameters /status

The reading from the B.I.T.E ., or recentmeasurement.

Plot filter / combiner parameters/ status


4.3.1.2.2 Secondary radar sensor (SSR ).

PARAMETERS UNITS / REMARKS Antenna tilt Deg. R.P.M rotations / minute. P.R.F Hz. Staggering ratio / pattern dimensionless/Hz. Instrumented range NM. Power KWs The reading from the powermeter of the

radar or the relative indication Mode interlace pattern/ ISLS/ IISLS / RSLS

3/A,C,1.2/ Yes(No) / Yes (No) / Yes (No).

Receiver sensitivity The relative indication from the B.I.T.E ., orrecent measurement.

Plot extractor parameters /status


Plot filter combinerparameters / status


4.3.2 Data Collection The person responsible for the evaluation shall ensure that the recordingcontains sufficient quantity and quality of data for the measurements to beperformed. The recorded data shall comprise:• polished/filtered primary target reports;• polished/filtered secondary target reports;• polished/filtered combined target reports;• and additional messages as specified in the table below according to

analysis objectives:



Overall Technical Detailed TechnicalSpecialmessages

Recommended Yes Yes

Multilevelrecordings

Recommended Recommended Yes

NOTES1. Special messages are PSR and SSR RTQC messages, overload

indications, North crossing, etc. Special messages are present on thenormal operational output and therefore recorded together with the targetreports. The analysis of such messages is recommended since it can yielduseful information about the changes in status of the Sensor(s).

2. Multilevel recordings at different I/O interfaces of the radar sensor.

The target reports used for analysis shall comprise:

Overall Performance • Opportunity Traffic Technical Performance • Opportunity Traffic,

• Special Test Flights Detailed TechnicalPerformance

• Opportunity Traffic,• Special Test Flights,• Simulated Data

The following characteristics shall be used for judging acceptability of arecording for use in an evaluation of the overall performance. It may benecessary to adjust the recording parameter values to obtain sufficient quantityof data for reliable analysis results..

4.3.2.1 Recording.

Minimum Duration • High Density Traffic Areas (en-route or major TMA) 1hour,

• Medium Density Traffic Areas - 2 hours,• Low Density Traffic Areas - 4 hours

Minimum Quantity of Data • Probability of Detection - 200 chains >5 minutes perchain

• Accuracy Analyses - 150 chains• Systematic Error Estimation -200 chains >5 minutes

duration in cover of > 2 radars. System Configuration • Normal Operational configuration for prevailing traffic

and environment. Environment, Weather • No Anoprop conditions. or heavy Angel Activity or

abnormal conditions (e.g. jamming, interference)should be used to verify PSR / SSR overallperformance.

• For the site commissioning, of the Primary RadarSensor, data should be collected, under all seasonalconditions and if applicable ,also under anomalous-propagation periods (ANAPROP ).



Traffic • Recording shall be made in Peak Traffic times ifpossible.

4.3.2.2 Data Quality Recorded quality • >99% of recorded data shall be correctly recorded

and available for chaining.• Recording with excessive data transmission errors

shall not be used for analysis.

Recommendations 1) General. The reliability of the evaluation results is directly linked to thequantity and quality of the recorded data. The quantity of data necessary forthe evaluation is dependant on the purpose of the evaluation - For the purposeof this standard the evaluation objective is the “Overall Performance Analysis”of the sensor for the parameters defined in the EUROCONTROL SurveillanceStandard. The analysis methods described in this standard are based on the concept ofchains (chained target reports) which may be non-air traffic information -clultter, fruit, etc. To obtain consistent and reliable evaluation results over aperiod of time it is important that the chains used for analyses are chosencarefully and consistently. The types of chain chosen must be representativeof the air traffic in the airspace covered by the sensor. For example;Probability of Detection results based on chains of which 60% were correlatedclutter would not be considered reliable. 2) Data Collection Duration. The target report sample size is determined bythe parameters to be measured. The standard recommends that one datacollection should serve for all the parameter measurements in a campaign.Therefore the data collection duration should be adapted to provide sufficientdata for the analyses to be carried out. The general rule is - the more (longer)the better within the limitations of the analysis system and time available. Sinceanalysis system resources and time are often limited and traffic patternsirregular, the following recommendations should allow a reliable set of results tobe obtained for most sensors. To estimate the duration one of the principle parameters may be considered;Probability of Detection, Systematic Errors (multi-radar systems) or accuracy.The following example should clarify the principle: Probability of Detection: For a sensor with 160NM maximum range, a 6second scan rate and an average plots/scan rate of 50 SSR plots. Assumethat 95% of the SSR plots are from real targets (47 plots per scan). To obtain the sample size for the overall Detection Calculation the requirednumber of chains (200 of at least 5 minutes) requires (200 / 47) * 5 minutes =25 minutes of recording. If the coverage space is divided into Range/Azimuth/Height cells of say 20NMx 22.5 degrees x 50 FL then it is more useful to try to record at least twochains per cell. In this case the required duration can be linked to the samplesize required for each cell - say 20 target reports per cell. Thus we get the required sample size:



SampleSizeMaxRange

RangeCellSizeNAzimuthCells NHeightCells NPlotsPerCell= × × ×

For our radar - assuming 75% of cells have data the sample size is:

⇒ × × × × =16020

36020

70050

20 75% 30240 plots

Thus for 47 plots per scan the duration is:

⇒ × ≈30240

47606

150minutes

Therefore a 2 1/2 hour recording should yield sufficient data for the Pdcalculations

4.3.3 Data Analysis

The analysis of the Radar Sensor performance PSR or SSR shall result in theestimation of the performance parameters specified in the EUROCONTROLRadar Surveillance Standard. The analysis methods are described in thefollowing sections. The performance parameters are divided into :

• Primary sensor performance parameters (sections 5 and 6);

• Secondary sensor performance parameters (sections 7 and 8);

• PSR/SSR Data Combining (section 9);

• On-Site Processing Delay (section 10);

• Availability (section 11).

Recommendation. When opportunity traffic is used for the performanceanalysis the data should conform to the following criteria with regard to chaining, chain characteristics and position reconstruction :

i) Chaining.

The following criteria may be used to judge if chaining is sufficient beforeproceeding with the analyses. The criteria are to be applied to each sensor tobe measured:

• >90% of recorded data shall be chained.• >70% of chains are more than 5 minutes duration. Allowing 5% of chainsterminating within 5 minutes of start and beginning within 5 minutes of end ofrecording.

• <10% of chained data are in resolution state

• no test target chains are used in the analysis



The 5 minute rule is intended to promote the concept that the performance ofthe sensor can only be reliably measured when both the sensor and themeasurement tool are in stable condition.

ii)Position Reconstruction.

• Reconstruction Errors should be excluded from analysis using trajectoryreconstruction filtering .

Trajectory reconstruction filtering should be based on the concept of samplingthe generated reference trajectory (a posteriori) at short intervals (e.g. 1 sec)along the trajectory path and comparing the changes in the trajectory’sadjacent velocity components. These changes should be used in order tocompute either the trajectory’s acceleration or turn rate between the samplingintervals. These terms should then be compared against a user suppliedthreshold (e.g. 1g or 10 deg./s) in order to reject those trajectories where thebehaviour reflects either a highly manoeuvring target (e.g. high performancemilitary) or a trajectory reconstruction problem with a civil en-route target. Theprinciple is to restrict the analysis to using stable trajectories exhibiting ‘civil’aircraft characteristics.

An additional filtering criterion which should be used in conjunction with thetrajectory filter is minimum ground speed (e.g. 50 m/s)

4.4 Interpretation of results

The results of the overall performance analysis shall be interpreted to conformwith the figures for these performance parameters in the EUROCONTROLRadar Surveillance Standard. The results shall not be considered conformant ifin comparison they are worse than the corresponding value specified in theEUROCONTROL Radar Surveillance Standard.

Recommendation. In the event that the results are not conformant furtherinvestigation should be undertaken, as described in ANNEX A or /and ANNEXB.



5. PRIMARY SENSOR DETECTION PERFORMANCE PARAMETERSANALYSIS

5.1 General

The detection performance parameters of a Primary(PSR) sensor are:

• Probability of target position detection;

• False target reports rate.

5.2 Probability of target position detection

5.2.1 Data analysis

For the estimation, of the probability of the target position detection therecorded primary and combined target reports (at the output of the radarsensor) shall first be chained. The chaining function shall associate eachtarget report to one and only one trajectory, identified by an aircraft number.With this association the number of the expected target reports inside the CMVcan be calculated. The recorded target reports shall come from opportunitytraffic except the case of heavy ground clutter environment in which the targetreports shall come from test flights.

The Pd measurement shall be Sensor performance based but if multi-radarinformation is available, it shall be used to establish whether a target is presentin the CMV of the Radar sensor being analysed. In a monoradar evaluation the“expected number of target reports“ is taken to be the number of antennascans between the first and the last detection of the target. In the case ofspecial test flights the expected number of target reports equals to the numberof aircraft radar sensor beam encounters.

The overall probability of target position detection inside the CMV shall becalculated using the formula 5.1. Extrapolated and false target reports shall beexcluded from the calculation.

Pd =

The number of detected primary & combined target reportsThe number of expected primary & combined target reports

(5.1)

NOTE The number of detected target reports is defined as one target reportper scan per radar per target (chain ). In case of multiple plots and /ornon-combination the target report which best fits the true path of thetarget shall be used for the Pd calculation.

Recommendation. The chaining algorithm should be the Object Correlatorcurrently under use in RASS tool or equivalent.



5.2.2 Interpretation of results

The interpretation of the results shall be to assess the quality of the targetposition detection compared to that specified in the EUROCONTROLSurveillance Standard.



5.3 False target reports

5.3.1 Data analysis.

The analysis of the false target reports shall be based on the characteristicsand behaviour they exhibit which differentiates them from real aircraft reports.A chaining algorithm shall be applied to the recorded primary and combinedtarget reports at the output of the radar sensor. As a result chained data shallbe derived with the history and the characteristics of each target forming achain. Then the false target reports shall be identified by their particularcharacteristics which will include several of the following:

• they are pure primary reports except the case of ships carryingtransponders;

• they form tracks with short life and relative low speed;

• they appear, in high density in ground, sea, weather and angel clutterareas;

• they appear in a ring, around the radar sensor (sidelobes);

• they appear in pairs with azimuth separation less than the antennabeamwidth (splits).

For the overall performance the average number of false target reports perantenna scan shall be estimated.

Recommendation. The chaining algorithm should be the Object Correlatorcur-rently under use in RASS tool, developed jointly by EUROCONTROL andFAA or equivalent.

5.3.2 Interpretation of results.

The interpretation of the results shall be to assess the quality of the averagenumber of false target reports compared to the specified value in theEUROCONTROL Surveillance Standard.



6. PRIMARY SENSOR QUALITY PERFORMANCE PARAMETERS ANALYSIS

6.1 General

The quality performance parameters of a Primary (PSR) sensor are:

• Positional accuracy;

• Resolution.

6.2 Positional accuracy.

6.2.1 General

The positional accuracy is defined as “the measure of the difference betweenthe position of a target as reported by the sensor and the true position of thetarget at the time of detection”. We consider the reference position of the targetto be the true position. This reference position can be extracted either fromdata recorded at different input /output (I/O) interfaces of the radar sensorunder test (e.g. .I/O between primary receiver and primary signal processor orI/O between the radar sensor and the Radar Data Processing System at thecentre), or from DGPS positional data recorded on board a test flight aircraft.

We assume an error model as follows:

ρ m(t)=(1+κ)*ρ ref (t+δ t)+δρ+σρ (6.1)

θm(t)=θ ref(t+δ t)+δθ+σθ

ρ m = measured slant range;

ρ ref = reference slant range;

δρ = slant range bias error;

σρ = slant range random error;

κ = slant range gain error;

θm = measured azimuth;

θ ref = reference azimuth;

δθ = azimuth bias;

σθ = azimuth random error;

δ t = time stamp error;



The above error model is used in the MURATREC algorithm for the estimationof the systematic and random errors.

The time stamping error is only applicable when sensors fusion techniques areused in the RDPS system.The error model is based in addition on theassumption that there is a range clock bias error which is represented by theparameter κ.The bias errors are considered as fixed values corresponding (forrange and azimuth bias) to the mean random error.

The accuracy of the reference position shall be at least an order of magnitudebetter than the accuracy of the measured position of the target reports at theradar sensors output.

According to the EUROCONTROL Radar Surveillance Standards positionalaccuracy shall be expressed by the following categories of errors:

• systematic or bias errors;

• random errors;

• jumps.

The performance for systematic / bias errors shall be expressed by:

• slant range bias;

• slant range gain error;

• azimuth bias;

• time stamp error.

The performance for random errors shall be expressed by:

• slant range error standard deviation;

• azimuth error standard deviation.

NOTE - Jumps are target reports with errors in position three timeshigher or more than the standard deviation for range andazimuth

6.2.2 Data analysis

For the estimation of the overall positional accuracy the recorded primary (atthe output of the radar sensor) shall first be chained. Then a referencetrajectory shall be reconstructed for each target inside the CMV and comparedagainst the measured positions without any classification of the targets orgeographical limitations.



The reconstruction of the reference trajectory (for each target inside the CMV)shall be based:

a) on recorded target reports when:

a.1) at least part of the CMV is covered from another two radars ;

NOTE The sharing of coverage is most important for systematic errormeasurement . At least 50% of the chained data inthe CMV should beseen by two or more sensors if the results are to be reliable.

a.2) at least n trajectories can be built with a minimum of m target referencepositions. Where each target reference position shall be within the referenceposition accuracy stated in par. 6.2.1.

b)on multilevel recordings (e.g. recordings at the video level and at the plotlevel) when the a.1 and a.2 are not applicable.

c) on DGPS data (coming from test flights) time synchronised with therecorded target reports or any other reference positioning system. The DGPSposition of the target together with the corrected DGPS time should be takenas the reference . The DGPS position must be projected onto a common planefor comparison with the target report data. A stereographic projection using thesame earth model as the sensor under test is best.

Recommendation. The relative accuracy of the reference should be knowncompared to DGPS/GLONAS/EGMS system.For evaluations undertaken forEATCHIP the coordinate conversion algorithms should be those used by theRASS-C system (so-called MURATREC transformation algorithm).

From the comparison of the measured position and the reference position foreach target inside the CMV and assuming the model 6.1 the following errorsshall be estimated:

i) systematic (bias) errors:



• azimuth bias;


The systematic errors shall be represented by fixed numbers.

ii) random errors:

• slant range error;



• azimuth error.

The random errors shall be represented by the standard deviation of thedistribution they follow.

iii) positional jumps.

Because it is not possible with the existing methods to make a distinctionbetween positional jumps and false target reports the positional jumps arecounted as false target reports.

Recommendation The following algorithms should be applied:

a) Object Correlator or similar for the chaining and MURATREC or similarfor the trajectory reconstruction in the case that recorded multiradar data areavailable. MURATREC is a curve fitting technique using 4th order beta-splinescurrently under use in RASS tool developed jointly by EUROCONTROL andFAA.

b) RASS-S or equivalent when the analysis of multilevel recordings is used.

c) DGPS.


The interpretation of the results shall be to assess the quality of the overallpositional accuracy compared to that specified in the EUROCONTROL RadarSurveillance Standard.



6.3 Resolution.

6.3.1 General

According to the EUROCONTROL Radar Surveillance Standard “theresolution is the capability of the sensor to discriminate between two aircraft inclose proximity and to produce target reports for both. The probability ofdetection is applicable to each individual aircraft.”

Close proximity is defined for PSR as follows:

• slant range ≤ 2 * nominal (compressed) pulse width;

• azimuth ≤ 3 * nominal 3 dB beamwidth.

These areas are shown in Figure 6.1. This diagram indicates the relativeseparation - as it is seen by the Radar Sensor - between the two aircraft. Theorigin O of the axes coincides with the position of the first aircraft. The areasare:

• “isolated targets” area is represented by area 3 ;

• Close proximity area is represented by areas 1 and 2 ;

• No resolution requirement area is represented by area 1;

• PSR Resolution measurement area is represented by zone 3a.

The area 1 in which no resolution capabilities are required is defined by acorresponding difference in slant range <1.5 * nominal (compressed) pulsewidth and a difference in azimuth <1.5 * nominal 3 dB beamwidth

∆ρ (NM) (3) ± p*τ (3a) ± 2 τ (2) ± 1.5 τ (1) O ± 1.5 θb ± 3 θb ± q*θb ∆θ (Deg.) Figure 6.1



τ = nominal (compressed) pulse width in NM;

τ (NM) =τ (µsec) ∗ c / 2;

θb = nominal 3 dB beamwidth;

c = velocity of light = 161987 NM/sec;

p = range inclusion factor;

q = azimuth inclusion factor.

Inclusion factors are used to “concentrate” the results on portions of chainswhich are in within potential resolution (close proximity). If the factors p and qare not limited then the results for area 3a will be meaningless since most ofthe chains in the data set will fall into this category.

6.3.2 Data analysis

For the evaluation of the overall resolution of the radar sensor the probabilityof position detection for each individual target being in close proximity shall beestimated. For this the recorded primary and combined target reports at theoutput of the radar sensor shall first be chained, then a reference trajectoryshall be reconstructed for each target inside the CMV. The reconstruction ofthe reference trajectory shall be done as it is described in par. 6.2.2 above.Using this reference trajectory information an algorithm shall sort out all thetrajectory pairs with relative separation falling inside the shaded zone 3a whichis defined by 6.2.

|2τ| ≤ ∆ρ ≤ |p*τ| (6.2)

|3θb| ≤ ∆θ ≤ |q∗ θb|

From this information the algorithm shall calculate the number of expectedtarget reports with relative separation fulfilling the above (6.2). Then usingchaining information the detected target reports associated to the above pairsshall be sorted out.

All target reports used in the resolution analysis shall have a reference position.

The overall probability of detection for an individual target in resolution shall beestimated using the following formula :

Pd= The number of expected target reports in zone 3a

The number of detected target reports chained to trajectories in zone 3a

(6.3)




The interpretation of the results shall be to assess the quality of the resolutioncapability compared to that specified in the EUROCONTROL RadarSurveillance Standard.



7. SECONDARY SENSOR DETECTION PERFORMANCE PARAMETERSANALYSIS

7.1 General.

The detection performance parameters of a Secondary (SSR) sensor are:

• probability of target position detection;

• probability of code detection;

• false target reports ratio;

• multiple SSR target reports ratio.

7.2 Probability of target position detection.

7.2.1 Data analysis.

For the estimation of the probability of the target position detection the recordedsecondary and combined target reports at the output of the radar sensor shallfirst be chained. The chaining function shall associate each target report to oneand only one trajectory identified by an aircraft number (aircraft identification ).With this association the number of the expected target reports can becalculated. The Pd measurement shall be Sensor performance based butshall use multi-radar information, where available to determine whether a targetis present in the CMV of the Radar sensor to be analysed. In a monoradarevaluation the “expected number of target reports“ is taken to be the number ofantenna scans between the first and the last detection of the target.

The overall probability of target position detection, inside the CMV, shall becalculated using the formula 7.1. Extrapolated and false target reports shall beexcluded from the calculation.

Pd =

The number of detected secondary & combined target reportsThe number of expected secondary & combined target reports

(7.1)

⊗ ⊗ ⊗ ⊗ ⊗ ⊗ ⊗ ⊗ ∅ ∅ ⊗ ⊗ ⊗ ⊕ ∅ ⊗ ⊗ ⊗ ⊗ ⊗ ⊗ 1234-V 1234-I XXXX-V XXXX-I

Figure 7.1

The symbols used in the figure 7.1 denote the following:



• ⊗ ≡the code is validated and correct (17);

• ∅≡there is no detection (3);

• ≡ the code is correct but not validated (3);

• ≡ the code is incorrect but validated (2);

• ⊕ ≡ the code is incorrect and not validated (1).

So in figure 7.1 the Probability of detection equals to Pd = 23/26.

TE If a target report falls outside the “jump window” (ERSS) it is classifiedas a false target report . This is interpreted as if the target report was usedoperationally then it’s position may lead to erroneous interpretation of thetarget’s position for the purposes of radar separation. As the ERSSconsiders jumps to be classified as false target reports then for thepurposes of Probability Detection Analysis (PDA) any jump shall beconsidered as a missed target report for the respective sensor.

Recommendation The chaining method should be the Object Correlatorcurrently, under use in RASS tool or equivalent.


The interpretation of the results shall be to assess the quality of the probabilityof target position detection compared to that specified in the EUROCONTROLSurveillance Standard.



7.3 Probability of code detection .

7.3.1 Data analysis .

For the estimation of the overall probability of code detection, only thesecondary or combined target reports used for the calculation of the targetposition detection shall be taken into account . So only the target reports thatthe chaining process shall associate to an aircraft trajectory shall beconsidered.

The Pcd measurement shall be sensor performance based but shall usemulti-radar information where available to detect whether a code change is dueto a pilot action or to system malfunction.

The overall probability of Mode A or Mode C code detection shall be calculatedusing the following formula :

(7.2)

P = cd

The number of target reports with validated and correct Mode A

Pcd =The number of target reports with validated and correct Mode C

Mode A

Mode C

The number of detected target reports chained to trajectories

The number of detected target reports chained to trajectories

(7.3)

NOTES

1. The code validation of Mode A or Mode C is a process carried out bythe Radar sensor under question. The validation is a flagged indicationof the correctness of the Mode A/C message derived from the aboveprocess.

2. Correct means the Mode A/C code value corresponds to the current"correct" value for the associated trajectory. The correct value isdetermined and maintained by the analysis system.



3. The Correct Mode C value is calculated from the chained data usinginterpolation to estimate the likely Mode C value for a chain at instantduring the life of the chain. In the case where the Flight Level is known(GPS or Test Flight) then the reference Mode C may be fixed to theknown value.

4. The reference Mode A value must be synchronised with code changes.

If we apply the above formula for figure 7.1 Pcd = 17/23.

Recommendation. The chaining algorithm should be the Object Correlatorcurrently under use in RASS tool, developed jointly by EUROCONTROL andFAA or equivalent.

7.3.2 Interpretation of results .

The interpretation of the results shall be to assess the quality of the probabilityof code detection compared to that specified in the EUROCONTROLSurveillance standard.



7.4 False / Multiple SSR target reports ratio.

7.4.1 Data analysis .

For the estimation of the False / Multiple SSR target reports ratio thesecondary and combined target reports recorded at the output of the radarsensor shall at first be chained. As a result chain data shall be derived with thehistory and the characteristics of each target report forming a track. Then theFalse /Multiple target reports shall be sorted out based on the particularcharacteristics they possess which are generally the following:

a) False SSR target reports

• they are not synchronised ( asynchronous fruit which normally shall notappear at the output of the plot filter);

• they form track with relative short life. (synchronous fruit and second timearound replies ).

b) Multiple SSR target reports

• they may have the same A/C code as the real aircraft target reports butthey form tracks with relative short life and they appear in certain sectorsbounded, by the orientation and the size of reflecting surfaces (reflections);

• they appear in pairs with small azimuth separation less than the antennabeamwidth (splits );

• they appear in a ring ,around the radar sensor (sidelobes).

It is useful also to correlate the recorded and processed data with the HPD’s ofthe antenna of the radar sensor for the identification of the multiple SSR targetreports coming from sidelobes.

The False / Multiple SSR target reports rate shall be calculated using thefollowing formula :

R

Fal/Mul=

The number of False / Multiple SSR target reports The number of detected secondary & combined target reports

(7.4)

NOTE The denominator includes all detected targets i.e. a/c and false.

For the overall performance analysis the following ratios shall be calculated:



R =False The number of detected secondary & combined target reports

a)

b)R =

The number of detected secondary & combined target reports

The number of multiple SSR target reports

Multi

b.1)R = The number of multiple SSR target reports from splits

The number of detected secondary & combined target reports

b.2)

Splits

R = The number of multiple SSR target reports from reflectionsThe number of detected secondary & combined target reports

b.3)R

Refl.

= The number of multiple SSR target reports from sidelobesThe number of detected secondary & combined target reportsSidel.

The number of false SSR target reports (fruits, STAT) (7.5)

(7.6)

(7.7)

(7.8)

(7.9)

Recommendations

The following criteria should be applied to detect the false/multiple plots:

1) False plots The false plots are coming either from second time returns orfrom fruit (synchronous or un synchronous).

1.1) Criteria for False plots coming from fruit (synchronous or unsynchronous).

• False plot should not be combined;

• the mode A and mode C may be swapped in the plot message dependingon the mode interlace;

• the following inequalities should hold:

(ρr-ρf) > fruit minimum range difference = ∆ρmin

θr-θf ≤ fruit maximum azimuth difference = ∆θmax

The reference plot is the real plot and represents the real position of the targetsee figure 7.3.

1.2) Criteria for False plots coming from second time around replies.

• False plot should not be a combined plot;



• the mode A and mode C may be swapped in the plot message for 2ndtrace targets, depending on the mode interlace;

• the following inequalities should hold:

ρr-ρf -R≤ second time around maximum range difference = ∆ρmax

θr-θf ≤ second time around maximum azimuth difference = ∆θmax

The reference plot is the real plot and represents the real position of the targetsee figure 7.4.

Parameter Symbol Value fruit minimum range difference ∆ρmin 0.5 NM second time around maximum range difference ∆ρmax 10 NM fruit/sec. time around maximum azimuth difference ∆θmax 1°

2) Multiple plots. Multiple plots are coming from reflections , splits, sidelobes.

2.1) Criteria for multiple coming from reflections. The criteria to detectreflections are different for the reflections received from the main beam(multipaths) and from sidelobes.

2.1.1) Criteria for reflections inside the main beam (multipaths).

• The false plot has the same mode A code as the reference plot;

• the false plot has the same mode C code as the reference plot (if both ofthem are present);

• the multiple should satisfy all of the following conditions:

ρr-ρf ≤ multipath maximum range difference = ∆ρmax

θr-θf ≤ multipath maximum azimuth difference = ∆θmax

Parameter Symbol Value multipath maximum range difference ∆ρmax 0.0625 NM multipath maximum azimuth difference ∆θmax 0.05°

2.1.2) Criteria for reflections outside the main beam.

• The false plot has the same mode A code as the reference plot (validated);




• the multiple should satisfy the following conditions:

∆ρmin= minimum range difference <ρr-ρf ≤maximum range difference = ∆ρmax

∆θmin =minimum azimuth difference<θr-θf ≤maximum azimuth difference=∆θmax

Parameters Symbol Value reflection minimum range difference ∆ρmin 0.0625 NM reflection maximum range difference ∆ρmax 20 NM reflection minimum azimuth difference ∆θmin 5° reflection maximum azimuth difference ∆θmax 150°

NOTE: A useful parameter for analysis is to specify the realistic maximumrange of reflectors - say 20NM - beyond which no reflecting surfaceshould be large enough to cause any reflections.

2.2) Criteria for multiple coming from split plots.

Split replies are generated by the same aircraft producing more than one targetseparated by a small range and/or azimuth difference. The split plots aredivided into three subclasses:

• Range Split;

• Azimuth Split;

• Range/Azimuth Split.

The criteria are the following:

• the false plot has the same mode A code as the reference plot (eithervalidated or non-validated);


• the following conditions should hold :

i) for range/ azimuth split :

split minimum range difference<ρr-ρf | ≤ split maximum range difference

split minimum azimuth difference <θr-θf ≤ split maximum azimuth difference



ii) for range split:

split minimum range difference<ρr-ρf | ≤ split maximum range difference

0 <θr-θf ≤ split maximum azimuth difference

iii) for azimuth split:

0 <ρr-ρf | ≤ split maximum range difference

split minimum azimuth difference <θr-θf ≤ split maximum azimuth difference

Parameter Symbol Value Split minimum azimuth difference ∆θmin 0.05o

Split maximum azimuth difference ∆θmax 3.00o

Split minimum range difference ∆ρmin 0.0625 NM Split maximum range difference ∆ρmax 0.25 NM

2.3) Criteria for multiple coming from sidelobes.

False targets ,which appear due to the sidelobes, are generally caused by thenearest (i.e., highest) lobes and the backlobe (180 deg). The ringaround is aspecial type of sidelobes effect since the phenomena causing the ringaroundand sidelobes are same. However, a certain number of sidelobes shouldoccur to have a ringaround phenomenon. The ringaround false plots aregenerated by sidelobe interrogations are outside the main beam approximately10 degrees from the centroid of the true target. So the multiples are divided inthree subclasses:

• sidelobes;

• backlobes;

• ringaround.

The criteria are the following:

• the false plot has the same mode A code as the reference plot (validated);


• Range difference is a function of azimuth difference between the false andreference and the radial speed of the target (for ringaround);

• the multiple should satisfy the following conditions:

i) for sidelobe:



sidelobe minimum range difference<ρr-ρf | ≤ sidelobe maximum rangedifference;

sidelobe minimum azimuth difference <θr-θf ≤ sidelobe maximum azimuthdifference

ii) for backlobe:

backlobe minimum range difference<ρr-ρf | ≤ backdelobe maximum rangedifference;

backlobe minimum azimuth difference <θr-θf ≤ backdelobe maximumazimuth difference;

iii) for ringaround :

ρ i−{ { (tN-ti)* (ρN-ρ i) /(tN-t1) }+ρ1}≤ ,ringaround range tolerance

N ≥ ringaround minimum plot confirmation.

Assuming N plots in time order with ti, ρi, the time stamp and the range of theith plot.

Parameter Symbol Value Sidelobe minimum azimuth difference ∆θmin 3o

Sidelobe maximum azimuth difference ∆θmax 10o

Side/backlobe minimum range difference ∆ρmin 0.50NM Side/backlobe maximum range difference ∆ρmax 1.00NM Backlobe minimum azimuth difference ∆θmin 177o

Backlobe maximum azimuth difference ∆θmax 180o

Ringaround range tolerance ∆ρ 1NM Ringaround minimum plot confirmation N 10



Ring Around

Mul'Path

Azimuth separation (degrees)

Split Min Az

Ran

ge s

epar

atio

n (N

M)

Split MaxAz

Multipath Min Rng

SP Max Rng

Sidelobe Min Az Sidelobe Min AzBacklobe Min Az

Backlobe Min Az

SP Min Rng

Multipath Max Rng

Refl Min Rng

Refl Max Rng

Refl Min Az Refl Max Az

AzSplit

O deg

ONM

Side Lobe

Reflections

BackLobeRange/Az

SplitRangeSplit

Figure 7.2 Position difference between reference(true) and multiple (false )plot.

NOTE The above diagram assumes LVA antenna characteristics .

7.4.2 Interpretation of results.

The interpretation of the results shall be to assess the quality of the False /Multiple target reports ratios compared to the ones specified in theEUROCONTROL Surveillance Standard.



Figure 7.3 False Reply / plot from unwanted interrogation (Fruit).

Figure 7.4 Second Time around reply/plot.



8. SECONDARY SENSOR QUALITY PERFORMANCE PARAMETERSANALYSIS

8.1 General

The quality performance parameters of a Secondary Sensor (SSR) are:

• Positional accuracy;

• False code information;

• Resolution.

8.2 Positional accuracy.

8.2.1 General

The positional accuracy is defined as “the measure of the difference betweenthe position of a target as reported by the sensor and the true position of thetarget at the time of detection”. We consider the reference position of the targetto be the true position. This reference position can be extracted either fromdata recorded at different input /output (I/O) interfaces of the radar sensorunder test (e.g. I/O between monopulse receiver and monopulse signalprocessor or I/O between the radar sensor and the Radar Data ProcessingSystem at the centre), or from DGPS positional data recorded on board a testflight aircraft. We assume an error model as follows:

ρ m(t)=(1+κ)*ρ ref (t+δ t)+δρ+σρ (8.1)


ρ m = measured slant range

ρ ref = reference slant range

δρ = slant range bias error

σρ = slant range random error

κ = slant range gain error

θm = measured azimuth

θ ref = reference azimuth

δθ = azimuth bias

σθ = azimuth random error



δ t = time stamp error

The above error model is used in the MURATREC algorithm for the estimationof the systematic and random errors. The error model is also based on theassumption that there is a range gain κ - the range bias varies as a function ofrange. The gain may be due to an error in the range clock or some systematicpulse deformation /attenuation problem.

The time stamping error is only applicable when sensors fusion techniques areused in the RDPS system.

The bias errors are considered as fixed values corresponding for range andazimuth bias to the mean random error.

The accuracy of the reference position shall be at least an order of magnitude(10 times) better than the accuracy of the measured position of the targetreports at the radar sensors output.

According to the EUROCONTROL Radar Surveillance Standards positionalaccuracy shall be expressed by the following categories of errors:

• systematic or bias errors;

• random errors:

• jumps.

The performance for systematic / bias errors shall be expressed by:



• azimuth bias;


The performance for random errors shall be expressed by:

• slant range error standard deviation;

• azimuth error standard deviation.

NOTE- Jumps are target reports with errors in position three timeshigher or more than the standard deviation for range andazimuth. Jumps are single scan events.



8.2.2 Data analysis

For the estimation of the overall positional accuracy the recorded data shallat first be chained. Then a reference trajectory shall be reconstructed for eachtarget inside the CMV and compared against the measured positions withoutany classification of the targets or geographical limitations.

The reconstruction of the reference trajectory (for each target inside the CMV)shall be based:

a) on recorded target reports when:

a.1) at least part of the CMV is covered from another two radars;

NOTE Position reconstruction can only be reliable when the target is seen bytwo or more sensors . If more than 30% of the chained data are seenby only one sensor then the quality analysis results may be unreliable.

a.2) at least n trajectories can be built with a minimum of m target referencepositions. Where each target reference position shall be within the referenceposition accuracy stated in par. 8.2.1.

b) on multilevel recordings (e.g. recordings at the video level and at the plotlevel) when the a.1 and a.2 are not applicable.

c) on DGPS data (coming from test flights) time synchronized with therecorded target reports or any other reference positioning system. The DGPSposition of the target together with the corrected DGPS time should be takenas the reference. The DGPS information will normally be in Latitude/Longitudeand height above Mean Sea Level with coordinates in WGS84. The sensordata will normally be either Range/Azimuth/FL, X/Y local/FL or X/Y System/ FL.The coordinates for the sensors and system origin must be stated inWGS84.To chain the two sources of data and to use the DGPS position as areference both data sources must be projected onto a common coordinatesystem. Either a Stereographic system (height independent) or a x/y/FLsystem may be used. In the case of a mono-radar evaluation the system originshould be the sensor site coordinates, i.e. x/y local = x/y system. The GPSaltitude values or sensor FL values must also be normalised if errors are to beminimised - correction of Mode C or GPS Altitude values for the regional QNHat the sensor location and time of recording would be adequate.

From the comparison of the measured position and the reference position foreach target inside the CMV and assuming the model 8.1 the following errorsshall be estimated:

i) systematic (bias) errors:





• azimuth bias;


The systematic errors shall represented by fix numbers.

ii) random errors:


• azimuth error

The random errors shall be expressed by the standard deviation of thedistribution they follow.

iii) positional jumps

The positional jumps shall be expressed by the overall ratio of jumps asfollows:

The number of detected target reportsRj =The total number of jumps

(8.2)


a) Object Correlator or similar for the chaining and MURATREC or similarfor the trajectory reconstruction in the case that recorded multiradar data areavailable. MURATREC is a curve fitting technique using 4th order beta-splinescurrently under use in RASS tool.

b) RASS-S or equivalent when the analysis of multilevel recordings is used.


The interpretation of the results shall be to assess the quality of the overallpositional accuracy compared to that specified in the EUROCONTROL RadarSurveillance Standard.



8.3 False code information

8.3.1 General

The false code information according to the EUROCONTROL SurveillanceStandard shall be expressed by:

• overall false code ratio;

• validated false Mode A code ratio;

• validated false Mode C code ratio.

NOTES

1. The code validation of Mode A or Mode C is a process carried out bythe Radar sensor under question. The validation is a flaggedìndication of the correctness of the Mode A/C message derived fromthe above process.


8.3.2 Data analysis

For the estimation of the false code information only the secondary orcombined target reports used for the calculation of the probability of targetposition detection shall be taken into account . So only the target reports thatthe chaining process shall associate to an aircraft trajectory shall beconsidered.

The measurement shall be sensor performance based but shall use multi-radar information where available to detect whether a code change is due to apilot action or to system malfunction. The false code information shall beestimated using the following formulas:

• for the overall false code ratio:

R

Over/f=

The number of reports with incorrect Mode A or/and Mode C (valid or not)The number of detected secondary/combined reports chained to trajectories

(8.3)

• for the validated false Mode A codes ratio:



RA f/v

=The number of reports with incorrect and validated Mode A

The number of detected sec/combined reports chained to trajectories

(8.4)

• for the validated false Mode C codes ratio:

RC f/v

=The number of reports with incorrect and validated Mode CThe number of detected sec/combined reports chained to trajectories

(8.5)

If we apply the above formulas for the figure 7.1 we have the following:

• for the overall false code ratio R over/f = 3/23 ;

• for the validated false code ratio R f/v = 2/23.


The interpretation of the results shall be to assess the quality of the false codeinformation compared to that specified in the EUROCONTROL RadarSurveillance Standard.



8.4 Resolution.

8.4.1 General

According to the EUROCONTROL Radar Surveillance Standard “ theresolution is the capability of the sensor to discriminate between two aircraft inclose proximity and to produce target reports with correct code for both . Theprobability of position and code detection is applicable to each individualaircraft.”.

Close proximity is defined for SSR as follows:

• slant range ≤ 2 NM;

• azimuth ≤ 2 * nominal 3 dB interrogation beamwidth.

∆ρ (NM) ±∆ρ2 (2) (1) ±∆ρ1 (3) O ±∆θ1 ±∆θ2 ∆θ (deg.) Figure 8.1

∆θ 1 2 360= ∗ ∗∗

nf t

For:

• n (number of SSR interrogation modes) = 2

• f (interrogation repetition frequency) = 240 Hz

• t (antenna rotation period ) = 10 sec.



• ∆θ1= 0.6 Deg.

• ∆θ2 = 2 * nominal 3 dB interrogation beamwidth.

• ∆ρ1 = 0.05 NM

• ∆ρ2 = 2 NM

The 3dB beamwidth of a MSSR antenna is typically 2.5°.

8.4.2 Data analysis

For the evaluation of the overall resolution capability of the radar sensor theprobability of position and correct code detection for each individual target shallbe estimated. For this the recorded data shall at first to be chained then areference trajectory shall be reconstructed for each target inside the CMV. Thereconstruction of the reference trajectory shall be done as it is described inpar. 8.2.2 above. Using this reference trajectory information an algorithm shallfirst sort out all pairs of trajectories having parts falling inside the closeproximity area (Figure 8.1 thick line) and then define the parts falling insideareas 1, 2 and 3. Then the algorithm shall calculate the number of expectedtarget reports for each part of the trajectory and the total number of expectedtarget reports for each close proximity area. At last using the chaininginformation the number of detected target reports associated to trajectoriesinside the areas 1, 2, and 3 shall be calculated.

The overall probability of position detection Pd and correct code detectionPcd shall be estimated for the areas 1, 2 and 3 using the following formulas:

Pd=

Pcd=

Pcd

Mode A

The number of reports with correct and valid Mode A

Mode C=

The number of reports with correct and valid Mode C

The number of expected reports in close proximityThe number of detected reports chained to trajectories in close proximity

The number of detected reports chained to trajectories in close proximity

The number of detected reports chained to trajectories in close proximity

(8.7)

(8.8)

(8.9)


The interpretation of the results shall be to assess the quality of the resolutioncapability compared to that specified in the EUROCONTROL RadarSurveillance Standard.



9. PSR/SSR DATA COMBINING ANALYSIS

9.1 General

According to the EUROCONTROL Surveillance Standard PSR/SSR datacombining is the capability of the radar sensor to associate each antenna scanthe target reports of the same aircraft detected by the two sensors and tocombine these reports into a single target report. This capability shall beexpressed by the following parameters:

• overall probability of association (Pas);

• overall false association rate (Rfas).

An association is considered as false if the target reports from two unrelatedtargets detected by the two sensors have been associated.

The above are based on the following assumptions:

9.1.1 The PSR and SSR sensors are collocated and they have the same OCV(Operational Coverage Volume);

9.1.2 Only aircraft flying inside the above mentioned OCV who have active SSRtransponders will be detected as combined targets.

9.2 Data analysis

For the evaluation of the data combining capability of the radar sensor theoverall probability of association Pas and the overall false association rateRfas shall be estimated for the targets flying inside the OCV of the sensor.

For the estimation of the overall probability of association and the overall falseassociation rate the following formulas shall be used:

(9.1)

Pas = The number of expected combined reports

Rfas =

The number of detected correct combined reports

The number of detected false combined reportsThe number of detected combined reports (9.2)

NOTE Correct / false combined target report is a target report coming from acorrect / false association of a primary and a secondary target report.



Recommendation: Collimation analysis is an important aspect ofCombination Analysis, e.g. CMB target and PSR target in close proximity. Ifthe CMB position is derived form the SSR and the collimation error issignificant safe radar separation may be compromised.

NOTE Special analysis techniques outside the scope of this document arerequired for Non co-located Combined radars.


The interpretation of the results shall be to assess the quality of the datacombining capability of the sensor compared to that specified in theEUROCONTROL Surveillance Standard taking into account the assumptions9.1.1 and 9.1.2.



10 ON-SITE DELAY ANALYSIS

10.1 General

According to the EUROCONTROL Surveillance Standard the on site delay isthe time between the moment a radar target for a given aircraft is detected andthe moment when the corresponding report starts to be transmitted. Thesetarget reports are polished / filtered primary/secondary/combined target reportsproviding measured radar data after reduction of false data using mono-radarprocessing techniques.

10.2 Data analysis

To estimate the overall on site processing delay the time of detection for eachtarget and the time of transmission shall be recorded and their averagedifference shall be calculated. The recording shall be done at the level of:

• azimuth change pulses (ACP’s);

• video (receiver output);

• plot (plot extractor output);

• and filtered plot (plot combiner output).

NOTES

1. The target report on-site delay is the time expressed in secondsbetween the moment a radar target report for a given aircraft isdetected and the moment the corresponding report starts to betransmitted.

2. The time of detection is the time at which the centre of the antennabeam illuminated the target, i.e. the time at which the antenna was atthe target measured azimuth.

The above data shall be time stamped using a reference clock preferably GPS.The recordings shall be done in normal conditions i.e. overload periods shall beexcluded.


The interpretation of the results shall be to assess the quality of the on sitedelay compared to that specified in the EUROCONTROL SurveillanceStandard.



11. AVAILABILITY ANALYSIS

11.1 General

Availability is the probability that a system will be available for use at a givenrandom time or time interval. The term “available for use “ means that thesystem provides services within the specified limits. The availability can becategorised as follows:

• instantaneous availability A(t) which is the probability that the system willbe available at any random time t;

• mission availability Am(t) which is the probability that the system will beavailable at a time interval ∆t = t2-t1 and it is expressed by the followingformula;

At t

A t dtm

t

t

=−

∫1

2 1 1

2

( ) (11.1)

• steady-state availability As(t) which is the probability that the system willbe available for a very large period of time and it is expressed by thefollowing formula:

At

A t dts

t

( ) lim ( )∞ =→∞ ∫1

0(11.2)

For systems which are to be operated continuously as a radar system thesteady state availability shall be measured and from now on will be symbolisedby A and will be called simply Availability.

Using theoretical models we can predict the availability of a system. Forexample assuming that:

a) the failures and repairs follow exponential distributions;

b) the failure rate of the equipment is known and equals λ;

c) the repair rate of the equipment is known and equals µ..

The availability for a single system is given by the formula:

- A =+µ

µ λ(11.3)



the availability for a duplicated system in parallel configuration (one system ismain the other is stand-by) as in figure 11.1 is given by the formula:

Α =+

+ +µ λµ

µ λµ λ

2

2 2

22 2

(11.4)

A (λ, µ)

B (λ, µ)

Figure 11.1

These theoretical models are used during the design phase of a system for theprediction of the availability of the final product and during the operational life ofthe system to improve the availability of the system (e.g. by increasing therepair rate or decreasing the failure rate or both).

According to EUROCONTROL Surveillance Standard the availability of theradar data shall be expressed by the following characteristics:

• maximum outage time due to any given failure fmax;

• cumulative outage time due to all failures over a period of one year ftot;

• outage times due to scheduled actions s.

The above are illustrated in the figure 11.2.

a1 a2 a3 a4 a5 a6 a7

Operating

Non-operating s f1 f2 f3 f4 f5

Specified operating time

(one year)

Figure 11.2



f ftot i

i

N

==

∑1

(11.5)

fmax= max{f1, f2,...,fn} (11.6)

NOTE The term “failure” means failure of the sensor to provide data insidethe specified limits in the EUROCONTROL Surveillance Standard andmay be caused by a malfunction of the sensor’s hardware, firmwareor software.

11.2 Data analysis

The estimation of the availability of a sensor shall be based on the recordedoutage time due to any given failure of the system over a period of one year.

This can be done either by the sensor’s monitoring and control system or byan external equipment . We can define “the failure” of the sensor in manydifferent ways depending on the level of sophistication of the monitoring andcontrol system. One simple way is to define a failure as the non provision oftarget reports including field monitors for more than 2 antenna scans as it isdefined in the EUROCONTROL Surveillance Standard. This definition isbased on the assumption that the monitoring and control system of the sensorwill switch off the sensor or give an alarm to the user if the quality of theprovided data is below the specified level. This is not always the case becausethe existing monitoring and control systems are checking a very limitednumber of performance parameters usually in an indirect way.

The monitoring system of the primary sensor usually checks indirectly:

a) the Pd by checking the station parameters which are related to the detectionperformance such as:

a.1) in the transmission path:

• power;

• noise figure;

a.2) in the reception path:

• receiver sensitivity (using test target at RF level);

• MTI (using moving test target);

b)the alignment error by checking the position of active/passive reflectors.

The monitoring system of the Secondary sensor usually checks indirectly:



a) the Pd by checking:

a1) in the transmission path:

• power;

a2) in the reception path:

• receiver sensitivity using an injected test target.

b) the alignment error by checking:

• the position of the remote field monitor.

At present there is no available external equipment for RTQC(Real TimeQuality Control) (measuring on line all radar sensor performance parameters).The monitoring of the quality of the radar information is done at the existingsystems by the controller.

So for the existing systems we shall use the above described definition offailure assuming in addition that the monitoring system of the sensor issensitive to changes of the station parameters which have an impact to thedetection and quality performance of the sensor.

Recommendation The assessment of the availability of the radarsensor should be done either on site by the use of RASS-S (or equivalent), orat the centre by the use of RASS-C (or equivalent) or alternatively the radardata processing system using a sample of the radar data coming from theradar sensor connected to the centre. New radar sensors should have amonitoring system recording single and total non operating periods.

11.3 Interpretation of results The interpretation of the results shall be to assess the quality of the sensor’savailability compared to that specified in the EUROCONTROL SurveillanceStandard.


Edition 0.1 Working Draft Page A/1 June 1997

ANNEX A (RECOMMENDED) TECHNICAL PERFORMANCE ANALYSIS.

A.1 RADAR SENSOR PERFORMANCE ANALYSIS

A.1.1 General

The aim of the technical performance analysis is the in-depth and thoroughevaluation of the radar performance parameters so as they;

• can be predicted before the installation (factory tests);

• can be optimised (on site tests);

• can be measured at each point of the airspace volume under test(commissioning);

• and eventually can be checked and compared against the reference values(problem investigation, post modifications).

A.1.2 Analysis method

The technical performance analysis should be carried out using the same datacollected for an overall performance assessment. In this way the overallresults provide a link between the technical performance results and those ofother evaluations. The analysis technique is that of computer aided evaluationusing recorded data at the output of the sensor / input of the central radar dataprocessing system supported (if needed) by multilevel recordings at variousI/O interfaces, map data, digital terrain elevation data and visual observations.Chaining and trajectory reconstitution algorithms shall be applied to the data inorder to evaluate the performance parameters of the radar sensor under test.

A.1.3 Procedure

The procedure for the analysis shall be as follows :

A.1.3.1 Preparation for the analysis

For the technical performance analysis of the Radar Sensor, the conditions ofthe data collection shall be known but also the whole set up of the radarsensor. In this way the technical staff can find the reasons of possibledeviations of the sensors performance from the previous one.

So before the collection of the data the following shall be done :

A.1.3.1.1 Preparation of the Radar Sensor.

The integration of a radar sensor in the ATC system follows a series of tests,which are the following:


Page A/2 Working Draft Edition 0.1 June 1997

a) Acceptance tests. The radar sensor performance is checked against thespecifi-ed in the contract between the administration /agency and themanufacturer. Prior to these tests the manufacturer tunes / sets the radarsensor so as to meet the con-tractual requirements.

b) Commissioning .The radar sensor performance is analysed in order todefine the airspace volume where the radar sensor can provide radar servicesaccording to local operational requirements. This airspace volume is calledOperational Coverage Volume OCV.

The CMV shall be set to the OCV for all evaluation campaigns whose objectiveis to allow results comparison between different sensors and for submission toEATCHIP CIP. Subsequent modification to the system Functionality and/oroperational use may require the recalculation of the OCV. For this the CMVshall be included in the evaluation report (annex) so the correlation of resultsbetween evaluations will be more efficient.

Prior to the commissioning tests the manufacturer or the administration /agency shall configure the system so as to satisfy the local operationalrequirements. The settings of the radar sensor made during commissioningshall be used as a reference for all subsequent technical performanceanalyses. This shall be changed only if there is a replacement or modificationof a radar sensors equipment that affects the performance of the sensor (e.g.replacement of the antenna with another with a better polar diagram). Sobefore any technical performance analysis, the radar sensor shall be restoredto its initial condition (commissioning).

The radar sensor preparation refers to a series of measurements / checks-and if needed repair actions undertaken by the technical personnel to ensurethat the radar sensor is been restored to its initial condition. The term radarsensor includes the main, the standby equipment, the ancillary equipment (e.g.remote control and monitoring ,remote field monitor) and the standby power(e.g. UPS , power generator ).The Radar sensors are divided to:

• Primary radar sensors (PSR );

• Secondary radar sensors ( SSR ).

A.1.3.1.1.1 Primary radar sensor (PSR).

For the technical performance analysis of the Primary radar sensor thefollowing parameters shall be measured (if applicable):

PARAMETERS UNITS / REMARKS Antenna tilt Deg. Antenna polar diagrams Horizontal and vertical polar diagrams. R.P.M rotations / minute. P.R.F Hz = 1/sec. Instrumented range NM. M.T.I range NM Beam switching azimuth/range pattern.



Waveguide losses dB. Power KWs (peak or average). Spectrum AdBv / dBw = f (f) f in Hz. Pulse shape AV = f ( t ). Noise figure dB. M.D.S dBm. S.T.C / G.T.C AdB = f ( t ) Dynamic range dB. M.T.I / M.T.D filters response AdB = f ( f/v ) (v = Doppler speed f

= Doppler Shift) Plot extractor parameters/performance

Pd, Pfa,

Plot filter parameters /performance

Pd, Pfa, Overload reaction

The measurement methods for the above are described in Annex B.

A.1.3.1.1.2 Secondary radar sensor (SSR).

For the technical performance analysis of the secondary radar sensor thefollowing parameters shall be measured (if applicable):

PARAMETERS UNITS / REMARKS Antenna tilt Deg Antenna polar diagrams uplink and downlink

Horizontal and vertical polar diagrams

R.P.M rotations / minute P.R.F Hz = 1/ sec Staggering ratio / pattern dimensionless / Hz Instrumented range NM Power / power sectorization KWs / P = F(ϑ) Mode interlace pattern ISLS / IISLS sectorization RSLS Yes / No Pulse shape / pulse spacing A = f(t) / µsec Power spectrum P = f(f) Receiver sensitivity dBm Receiver dynamic range dB Receiver bandwidth A = f(f) Plot extractor parameters Plot extractor performance a) Pd, Pfa, Pcv; b) Defruiting;

c)Degarbling; Plot filter combinerparameters

Plot filter combiner perfor-mance /

a)Pd, Pfa Pcv;b)Reflection rejection; Overload reaction

The measurement methods for the above are described in Annex B.

A.1.3.1.2 Environmental measurements



The radar sensor (PSR / SSR) is a decision making system. By sampling anairspace volume (coverage volume) and applying sophisticated dataprocessing techniques the system decides about the presence or not oftargets of interest inside the airspace volume under test. This process is calledtarget detection / identification. The radar sensor detection / identificationcapability has physical limitations (e.g. due to the screening effect) and it isstrongly affected by the external conditions. The radar sensor performanceshould be analysed using mainly recorded data coming from opportunity traffic.

The term environment in this document defines not only the external to thedata sample factors (i.e. weather, jamming, lobing etc.), but also the specificcharacteristics / MOF (Mode Of Flight), of the data sample, that may affect theradar performance (i.e. transponder performance, traffic density, etc.). Theabove factors shall be identified, in order to evaluate their effect to the results ofthe analysis. In this sense the environmental factors that affect the technicalperformance of the primary sensor are the following:

• external interference / jamming;

• lobing;

• clutter areas / density;

• air-route structure;

• mode of flight(MOF);

• distance to the neighbouring a/c (resolution limitations);

• radar cross section distribution.

For the secondary radar sensor the environmental factors are the following:

• external interference / jamming;

• lobing;

• interrogation rate, sidelobe suppression rate, TCAS operation;

• transponder performance;

• air-route structure;

• mode of flight (MOF);

• distance to the neighbouring a/c (resolution limitations);

• reflectors/multipath effects.

These factors can either be identified by the analysis tool or by the use ofspecial test set-ups. The level of testing depends on the measurementcampaign (i.e. acceptance tests, commissioning, post modification ).



A.1.3.1.2.1 Environmental factors for the Primary radar sensor.

The environmental factors affecting the performance of the primary radarsensor are the following:

A.1.3.1.2.1.1 External interference / jamming.

For acceptance tests /commissioning all the interfering / jamming sources andtheir characteristics in the frequency and in the time domain shall be defined.This shall be done either by analysing the spectrum at the output of thereceiver by using special tools (before data collection) or using the recordeddata at the output of the radar sensor with the transmitter switched to thedummy load.

A.1.3.1.2.1.2 Lobing.

The theoretical lobing diagram / s of the sensor antenna shall be calculated.The calculation shall use digital terrain elevation data and the antenna verticalpolar diagram

A.1.3.1.2.1.3 Clutter areas / density.

The areas of ground and sea clutter shall be identified using map data . Whenit is needed the clutter density shall be measured, either by recording the videoat the output of the receiver, or by using special tools.

A.1.3.1.2.1.4 Air-route structure.

The structure of the air-routes creates certain flight patterns (i.e. tangentialflights) that affect the radar detection performance. So this effect shall be id-entified and used for the classification of the data according to the aspect angleto the sensor.

A.1.3.1.2.1.5 Mode of flight (MOF).

The performance of the MTI/MTD depends on the radial (to the radar sensor)speed of the target. In the case that the plot filter combiner uses tracking, theMOF of the target may degrade the radar sensor detection performance. Forthis the MOF of each target shall be identified. This shall be done using thereconstituted trajectory information.

A.1.3.1.2.1.6 Distance to the neighbouring a/c (resolution limitations).

The radar sensor performance is degraded, when the targets are in closeproximity (resolution limitations).These cases shall to be identified and the datasample shall be classified accordingly.

A.1.3.1.2.1.7 Radar cross section distribution.

The primary radar sensor detection performance depends on the radar crosssection of the target. An estimation of the radar cross section distribution of thedata sample can be done using video recordings at the output of the receiver.



A.1.3.1.2.2 Environmental factors for the Secondary radar sensor.

The environmental factors affecting the performance of the secondary radarsensor are the following:

A.1.3.1.2.2.1 External interference / jamming.

For acceptance tests /commissioning all the interfering / jamming sources andtheir characteristics in the frequency and in the time domain shall be defined.This shall be done either by analysing the spectrum at the output of thereceiver by using special tools (before data collection) or using the recordeddata at the output of the radar sensor with the transmitter switched to thedummy load.

A.1.3.1.2.2.2 Lobing.

The theoretical lobing diagram / s of the sensor antenna, for uplink and down-link, shall be calculated. The calculation shall use digital terrain elevation dataand the antenna vertical polar diagram.

A.1.3.1.2.2.3 Interrogation rate, sidelobe suppression rate, TCAS operation.

The interrogation rate, the sidelobe suppression rate and the impact from theTCAS operation inside the CMV shall be measured and taken into account inthe analysis of the performance of the radar sensor.

A.1.3.1.2.2.4 Transponder performance.

According to EUROCONTROL MTPA measurements about 10% of alltransponders operate more or less outside ICAO tolerances. For this thetransponder performance of the data sample shall be measured. This shall bedone either by using multiradar data or by using special tools.

A.1.3.1.2.2.5 Air-route structure.

The structure of the air-routes creates certain flight patterns (i.e. tangentialflights) that affect the radar detection performance (i.e. shielding of thetransponder antenna). So this effect shall be identified and the data sampleshall be classified according to the aspect angle to the sensor.

A.1.3.1.2.2.6 Mode of flight (MOF).

In the case, that the plot filter combiner uses tracking, the MOF of the targetmay degrade the radar sensor performance. For this the MOF of each targetshall be identified .This shall be done using the reconstituted trajectoryinformation.

A.1.3.1.2.2.7 Distance to the neighbouring a/c (resolution limitations).

The radar sensor performance is degraded (position and code detection),when the targets are in close proximity (resolution limitations) .These casesshall to be identified and the data sample shall be classified accordingly.



A.1.3.1.2.2.8 Reflectors/ Multipath effects.

The reflectors (reflecting surfaces) shall be identified and classified using mapdata in two classes permanent and temporary. The recorded data shall also bechecked regularly for false targets coming from multipath effects and theperiod and area shall be identified.

A.1.3.1.3 Definition of the Coverage Measurement Volume (CMV)

For the site acceptance and the site commissioning the CMV shall clearly bedefined, before the collection of data, using the contractual / operationalrequire-ments, digital terrain elevation data and theoretical calculations of thecoverage. In all other cases the CMV shall be the OCV.

A.1.3.2 Data collection

See par. 4.3.2.

A.1.3.3 Data classification

Input classification is a general scientific approach when dealing with analysisof the behaviour of complex non-linear systems. In experiments to measureany physical variable one tries to control all conditions that may be of influenceto the results. The same principles are applicable to radar performanceanalysis. Therefore a very important part of the measurement is to find welldefined input classes. This means that the main factors that have an influenceon the (performance) parameter to be measured shall be identified and each ofthem shall be used as a separate dimension in the multidimensionalmeasurement space. This should lead to consistent results ,which means thatwhen comparing the measured Pd values derived from two different data sets,for one and the same input class, the only reason of difference is theperformance of the radar.In practice we can only try to reach this ideal, limitedby our resources. The approach that is taken is meant to provide an efficientsolution that is sufficient to reach our analysis goals.Input parameters areconditions or variables of processes that have a significant impact on theperformance to be measured. In the following paragraph a non exhaustiveinventory of such parameters is given.

A.1.3.3 .1 Inventory of input parameters

Input classification used in an evaluation at the measured target report level ofa system may be restricted in the parameters available. Three generic groupsof Input classes are defined; Evaluation Static, Analysis level Static andAnalysis level Dynamic. Static Input classes are those which do not (or shouldnot) change during the evaluation or an Analysis. Dynamic classes are thosewhich do change by their nature or at the request of the system operator.Dynamic classes may be either sensor or evaluation system parameters (e.g.display selections) and are intended for controlling the measurement.Additionally classes may have discrete or continuous values. The followinglists identify examples of Static and Dynamic classes at the Evaluation andAnalysis Levels.



A.1.3.3 .1.1 Evaluation Level - Static Input Classes

Two groups of static Input Classes at the evaluation level are foreseen:

a) Radar system parameters:

• radar type;

• maximum range ;prf; polarisation ;

• HPD, VPD;

• STC; transmitter power;

• resolution characteristics;

• MTI/MTD characteristics ;

• on site plot filter parameters etc.

b) geographical oriented, site dependent (time invariant):

• antenna position and height;

• terrain properties;

• screening angles ;

• ground/sea clutter areas etc.

A.1.3.3 .1.2 Analysis Level - Static Input Classes

• Coverage Measurement Volume

• Airspace volumes

• Environment - Time, Area

• Flight Level Ranges

• Range Azimuth Segments

A.1.3.3.1.3 Analysis Level - Dynamic Input Classes

The table below gives an extensive, but not exhaustive, list of dynamic inputclasses for use at the Analysis level. Many classes are linked to a particularanalysis whilst others may be employed in any analysis

Time The time would be split into discrete intervalsPlot Type Type of the plot PR/SSR/COMBA Invalidated If the mode A code of the plot is InvalidatedA Incorrect If the mode A code of the plot is assessed to be incorrect



A Absent If the mode A code of the plot is absentA Garbled If the mode A code is garbledC Invalidated If the mode C code of the plot is InvalidatedC Incorrect If the mode C code is assessed to be IncorrectC Absent If the mode C code is AbsentC Garbled If the mode C code is garbledC Out of Spec If the mode C code is Out of Spec (FL-12 ..FL700)False If the plot is identified as falseResolution State If the chain/plot occurred during a resolution incidentResolution Distance Distance between targets in close proximityChain Class The classification of the chain (civil, military etc.)Chain Length The length of chains in discrete stepsMOF The 3 Modes of Flight - Longitudinal, Transversal and

Vertical of the reference trajectory at the time of the plotRange The range would be split into discrete stepsAzimuth The azimuth would be split into discrete stepsX The X would be split into discrete stepsY The Y would be split into discrete stepsMode C The mode C value would be split into discrete stepsAltitude The altitude would be split into discrete stepsElevation Angle The elevation angle would be split into discrete stepsVisibility Class Visible, Not Visible, Undetermined, Not ApplicableCone Of Silence The target report is in or out of the Sensor Cone of

Silence or undetermined.Mode C Different Difference between reference Mode C and measured

mode C. N.B. this is the actual difference between themeasured and reference not the assessed correctness

Active Transponder If the transponder is presumed to be switched onBad Transponder Evaluation system has unambiguously identified a

transponder errorActive Mode C If the aircraft with a transponder is sending Mode CMode A Group Possibly Static but defined sets of mode A codesMulti-RadarSegment

Areas where the radar is seen by multiple radars

A.1.3.4 Data Analysis

The data analysis shall result in a detailed evaluation the Radar Sensor (PSR/SSR) performance parameters specified in the EUROCONTROL RadarSurveillance Standard. The methods for the analysis, are described in the follo-wing paragraphs. The performance parameters are divided into:

• Primary sensor performance parameters;

• Secondary sensor performance parameters;



• PSR/SSR Data Combining;

• On-Site Processing Delay;

• Availability.

A.1.3.5 Presentation of results

The results of the performance parameters analysis shall be given in anappropriate form. The figures A-4, A-5, A-6, A-7, A-8 are typical examples ofpresentation of the results taken from RASS systems. In the case ofacceptance testing or commissioning the above results shall be correlatedmanually or preferably automatically with screening data to give the Coverageof the sensor in a form of Polar (Horizontal) diagrams for selected Flight Levelsand Vertical diagrams graduated for selected azimuths (Fringe Envelopes).

A.1.3.6 Interpretation of results

The results of the technical performance analysis of the radar sensor duringacceptance / commissioning testing shall define the Coverage. During theoperational life of the system it shall be possible to identify degradation of theperformance using results from baseline measurement campaign(i.e.commissioning).



A.2 PRIMARY SENSOR DETECTION PERFORMANCE PARAMETERSANALYSIS

A.2.1 General

The detection performance parameters, of a Primary(PSR) sensor, are:

Probability of target position detection;

False target reports rate.

A.2.2 Probability of target position detection


For the technical performance analysis of the radar sensor the data shall beclassified manually or automatically, as a function of :

• distance to neighbouring aircraft (resolution limitations)

• radar cross section taking into account the aspect angle (if possible);

• Doppler speed and Mode of Flight (MOF );

• clutter/interference conditions (ground sea and weather clutter ).

Any extrapolated target reports shall be identified and removed from theanalysis.

The above classification is justified by the simplified formula A.2.1which gives the average probability of detection at the output of an ideal IFreceiver, in the presence of white noise, in relation to the probability of falsealarms and the signal-to-noise ratio(of the target).

<Pd>=(Pfa)1

1+S/NS =2* σ2 (A.2.1)

Pfa ≡ the probability of false alarm ;

S ≡The signal power;

N ≡ The noise power;

σ ≡ the mean cross section of the target.

In the presence of clutter the noise power shall be substituted by theN=N0+C where C is the clutter residue at the output of the MTI / MTD in thiscase the signal power S depends on the radial speed of the target (Dopplerspeed). In the presence of RF interference not rejected by the receiverthen N should be substituted by I=N+Io ( Io is the interference power). Themean cross section of the target σ depends also on the aspect angle of thetarget. The probability of detection is also affected by the presence of other a/c



near to the target (the adjacent a/c can be considered as a very stronginterference) and in case of the use of tracking for plot filtering by the Mode OfFlight of the target.

A.2.2.2 Data analysis

For the estimation, of the probability of the target position detection theprimary and combined target reports recorded at the output of the radar sensorshall first be chained. The chaining function shall associate each target reportto one and only one trajectory identified by an aircraft number. With thisassociation the number of the expected target reports inside the CMV can becalculated and the gaps due to detection misses identified. The recorded targetreports shall come from opportunity traffic except the case of heavy groundclutter environment in which the target reports shall come from test flights.

The Pd measurement shall be Sensor performance based but shalluse multi-radar information where available to determine whether a target ispresent in the CMV of the Radar sensor to be analysed. In a monoradarevaluation the “expected number of target reports“ is taken to be the number ofantenna scans between the first and the last detection of the target. In the caseof special test flights the expected number of target reports equals to thenumber of aircraft Radar Sensor beam encounters.

For the technical performance analysis based on the opportunitytraffic the CMV shall be subdivided in elementary three dimensional cellsand the Pd inside each cell shall be estimated. The size of the cell dependson the required accuracy of the measurement and actually from the numberof the expected target reports inside the cell. The recommended default cellsize for an sensor are given below, the sizes may be adjusted to suit localrequirements, however when comparing results between differentevaluations consistent cell sizes must be used.

sensor Range cellsize (NM)

Azimuth cellsize (deg)

FL cellsize (FL)

FL Limits

En- Route 20 20 50 12 - 450 TMA 10 20 20 12 - 200

The probability of target position detection of a cell shall be calculated using theformula :

Pd =

The number of detected primary & combined target reportsThe number of expected primary & combined target reports

(A.2.2)

The calculation shall not take into account any extrapolated targetreport or false target report. For the test flights or individual flights, theprobability of detection of each point of the trajectory and the averageprobability shall be calculated. The calculation of the Pd of a point of atrajectory shall be based on the above formula (A.2), using a sliding window



whose centre is the point of the trajectory under test see figure A1. This shallbe called elementary or local Pdi.

The <Pd> (average) of the trajectory shall be calculated by theformula A.2.2.

i = ki = j

Pdk Pdj

Figure A-1

Recommendation The length of the sliding window should be equal to9.

When opportunity traffic is used the Pd for the following class and itssubclasses of targets shall be estimated :

Class A outside the close proximity area (area 3 figure A-2).

Subclasses of A:

• targets flying over ground clutter;

• targets flying over sea clutter;

• targets flying in weather clutter and over ground or sea clutter;

• tangential flying targets.

The above subclasses shall be subdivided as a function of the Dopplerspeed of the target the Mode of Flight (if tracking is used for plot filtering) and ifit is possible (using video recordings or flight plan information) of the targetcross section area.

The estimation of the Pd for the targets inside the close proximity area(areas 1a, 1, and 2 figure A-2 ) Class B it is related to the resolutioncapabilities of the radar sensor and it is treated in the relevant paragraph A.3.3.

Recommendation The chaining method should be the ObjectCorrelator currently under use in RASS tool, or equivalent .




The Pd shall be presented in :

• Horizontal polar(for selected flight levels) and Vertical polar (for selectedazimuthal sectors) diagrams graduated in discrete detection bands such ase.g. 50%, 50-80%, 80-90%, 90-95%, 95-98%, 98-100%;

• Overall Figures (for all the subclasses of targets) derived from themean detection values, for each detection cell in the calculation;

• Vertical diagrams in the case of special test flights, or when the majority ofthe target reports are combined (there is height information from the SSRtarget report). These shall be in a form of iso-Pd lines drawn for selectedazimuths;

• Horizontal polar and Vertical polar scattergraphs for the missesgenerated by the chaining process;

• Distribution in space and time and the size of the detection gaps .

An example of the above is given in Figures A-3, A-4, A-5. Thehorizontal polar diagrams shall be overlaid on an aeronautical map of the radarsensor site.


In order that the results of the Pd analysis may interpreted correctlyand be compared against specified figures (acceptance tests) or measuredfigures (previous campaigns) the data sample shall be strictly controlledregarding the distance to neighbouring a/c(resolution limitations) andadditionally the:

• radar cross sections(taking into account the aspect angle of the targets);

• the Doppler speed of the target;

• the clutter/ interference conditions ;

For this, in the case of site acceptance tests special test flights areconsidered mandatory especially if there is heavy ground clutter and nomultiradar coverage.

Recommendation The user must be aware that the Pd results for cells withonly one chain may not normally be used for judging the sensor Pdperformance . However data in such cells may be used for further analysisand problem investigation. In the situation where only one chain is present andthe Pd is poor the benefit of the doubt should be given to the sensor unless it iscertain that the target was well visible.



A.2.3 False target reports

A.2.3.1 Data classification.

The data shall be classified by their generic cause in two classes:

Class A. False targets generated by external / internal interferingsources (noise, internal or external interference).

Class B. False targets generated by unwanted echoes. This classshall be subdivided into the following subclasses :

Subclass B1. False targets generated by true aircraft :

• sidelobes;

• splits;

• positional jumps.

Subclass B2. False targets generated by non aircraft targets :

• ground clutter;

• sea clutter;

• weather clutter;

• angel clutter (birds, insects, anaprop , atmospheric echoes );

• ships, cars.

A.2.3.2 Data analysis.

The analysis of the false target reports shall be based on the differentcharacteristics and behaviour that appear from the true aircraft targets. Achaining algorithm shall be applied to the recorded data. As a result chaineddata shall be derived with the history and the characteristics of each targetforming a chain. Then the false target reports shall be sorted out based on theparticular characteristics they possess which are the following :

• they are pure primary reports except the case of ships or remote passive /active reflectors;

• they form tracks with short life and relative low speed;

• they appear, in high density in ground and sea clutter areas;

• they appear in a ring around the radar sensor (sidelobes);

• they appear in pairs with azimuth separation less than the antennabeamwidth.(splits).



For the technical performance analysis each class of false targetreports shall be estimated. To this an algorithm shall correlate the recordeddata with map data (from an aeronautical map of the site of the radar sensor)for the identification of false target reports coming from clutter and with theantenna Horizontal Polar Diagrams to identify sidelobe effects. An indication ofthe amount of the false target reports generated by noise and interference andthe location of the interfering sources can be derived by recording the outputwhen the sensor is in standby mode (the transmitter shall transmit to thedummy load) and all associated receiver and processing thresholds shall beallowed to stabilised. A recording of 10 to 20 minutes per channel would beprobably be sufficient. An alternative method for the estimation of the totalnumber of false target reports to the above is the use of visual observations.

Recommendation. For the Chaining the Object Correlator algorithmshould be applied. For the correlation of the recorded data with horizontal polardiagrams RASS-S should be used.

A.2.3.3 Presentation of results.

The results shall be presented in a table, showing all the categories offalse target reports. Also on a aeronautical map of the site of the radar sensor,the position and the number of false target reports shall be indicated.

A.2.3.4 Interpretation of results.

In order that the results of the false targets reports analysis mayinterpreted correctly and be compared against specified figures (acceptancetests) or measured figures (previous campaigns) the data sample shall besupported by visual observations (i.e. to sort out data that appear to be falsetargets but that are real targets forming sort life tracks due to detection missescaused by screening or lobing effects.) and controlled regarding the source ofthe false target report to:

• non-aircraft objects (i.e. interference, noise, clutter, ships, cars);

• aircrafts (i.e. sidelobes, splits, multiple time around.



A.3 PRIMARY SENSOR QUALITY PERFORMANCE PARAMETERS ANALYSIS

A.3.1 General

The quality performance parameters of a Primary (PSR) sensor are :

• Positional accuracy ;

• Resolution.

A.3.2 Positional accuracy.

A.3.2.1 General

The positional accuracy is defined as “the measure of the differencebetween the position of a target as reported by the sensor and the true positionof the target at the time of detection”. We consider as the true position of thetarget a reference position. This reference position can be extracted eitherfrom data recorded at different input /output (I/O) interfaces of the radar sensorunder test (e.g. .I/O between primary receiver and primary signal processor orI/O between the radar sensor and the Radar Data Processing System at thecentre), or from DGPS positional data recorded on board a test flight aircraft.

We assume an error model as follows :

ρ m(t)=(1+κ)*ρ ref (t+δ t)+δρ+σρ (A.3.1)


ρ m = measured slant range;

ρ ref = reference slant range;

δρ = slant range bias error;

σρ = slant range random error;

κ = slant range gain error;

θm = measured azimuth;

θ ref = reference azimuth;

δθ = azimuth bias;

σθ = azimuth random error;

δ t = time stamp error.

The time stamping error is only applicable when sensors fusiontechniques are used in the RDPS system.The error model is based in additionon the assumption that there is a range clock bias error which is represented



by the parameter κ.The bias errors are considered as fixed valuescorresponding for range and azimuth bias to the mean random error.

The accuracy of the reference position shall be at least an order ofmagnitude better than the accuracy of the measured position of the targetreports at the radar sensors output.

According to the EUROCONTROL Radar Surveillance Standardspositional accuracy shall be expressed by the following categories of errors :

• systematic or bias errors ;

• random errors :

• jumps.

The performance for systematic / bias errors shall be expressed by :

• slant range bias ;

• slant range gain error ;

• azimuth bias ;


The performance for random errors shall be expressed by :

• slant range error standard deviation ;

• azimuth error standard deviation .

NOTE- Jumps are target reports with errors in position threetimes higher or more than the standard deviation for range.and azimuth .


For the technical performance analysis of the radar sensor the datashall first to be classified in accordance to the distance to neighbouringaircrafts and then in accordance to:

• radar cross section taking into account the aspect angle;

• Mode of Flight (MOF )(Doppler speed);

• environmental conditions ( ground, sea, weather clutter conditions, Theabove classification is based on the following theoretical aspects.

For an ideal receiver the minimum measurement errors for targets infree space (in presence of white noise only) for range and azimuth are:

• σr = c/2*β*√ (S/N) (A.3.2)



• σθ ≡0.53*θ/√ (S/N)

β ≡ rms signal bandwidth = 1/τ;

S/N ≡ signal to noise ratio;

c≡ velocity of the light;

θ ≡half-power beamwidth .

The signal power at the detector input depends on the cross section ofthe target. If the target flies over a clutter area (ground or sea clutter) or inweather clutter the standard deviations depends on the signal to clutter ratio(S/C). At the signal processor output -after the MTI/ MTD processing- thesignal to clutter ratio depends on the targets Doppler speed. More generally theerrors depend on the signal to interference ratio (S/I), if we define asinterference every signal that interferes the useful signal. In that sense theneighbouring aircrafts shall be considered as a very strong interfering source ifthere are in the close proximity (see A.3.1). rf interferences).


For the estimation of the positional accuracy the recorded primaryand combined target reports (at the output of the radar sensor) shall first bechained. Then a reference trajectory shall be reconstructed for each targetinside the CMV and compared against the measured positions without anyclassification of the targets or geographical limitations.

The reconstruction of the reference trajectory (for each target inside theCMV) shall be based :

a) on recorded target reports when :


NOTE The sharing of coverage is most important for systematic errormeasurement . At least 50% of the chained data inthe CMV should beseen by two or more sensors if the results are to be reliable.

a.2)at least n trajectories can be built with a minimum of m targetreference positions. Where each target reference position shall be within thereference position accuracy stated in par. 6.2.1.

b)on multilevel recordings (e.g. recordings at the video level and at theplot level) when the a.1 and a.2 are not applicable.

c) on DGPS data (coming from test flights) time synchronised with therecorded target reports or any other reference positioning system. The DGPSposition of the target together with the corrected DGPS time should be takenas the reference . The DGPS position must be projected onto a common planefor comparison with the target report data. A stereographic projection using thesame earth model as the sensor’s under test is best. In the case of mono-radar evaluation the earth model of the host RDPS shall be chosen.



From the comparison of the measured position and the referenceposition for each target inside the CMV and assuming the model A.4 thefollowing errors shall be estimated:

i) systematic (bias) errors :



• azimuth bias;


The systematic errors shall be represented by fix numbers.

ii) random errors :


• azimuth error

The random errors shall be represented by the standard deviation ofthe distribution they follow.


Because it is not possible with the existing methods to make adistinction between positional jumps and false target reports the positionaljumps are counted as false target reports. The random errors shall beestimated for the following classes and subclasses of targets :

Class A : targets outside the close proximity area (area 3 figure A-2).

Class B : targets inside the close proximity areas ( areas 1a, 1 and 2figure A-2). Subclasses of A and B :

• targets flying over ground /sea clutter;

• targets flying in weather clutter and over ground / sea clutter;

• tangential flying targets;

And if possible for subclasses of the above based on to the Dopplerspeed of the target, the Mode of Flight (if tracking is used for plot filtering) andthe target’s cross section area.

Recommendation The following algorithms should be applied :

a) Object Correlator or equivalent for the chaining and MURATRECor equivalent for the trajectory reconstruction in the case that recordedmultiradar data are available.



b) RASS-S or equivalent when multilevel recordings are used.


The random errors shall be presented in histograms showing thedistribution they follow figure A-7 is an example of such an evaluation made byRASS-C tool. A quick way to detect sensor’s malfunctions is the use ofscattergraphs as the one in figure A-8 where large errors in certain azimuthsindicate probable malfunction of the sensor in this sector.


In order that the results of the accuracy analysis may interpretedcorrectly and be compared against specified figures (acceptance tests) ormeasured figures (previous campaigns) the data sample shall be strictlycontrolled regarding mainly the distance to neighbouring a/c (close proximityclassification) and additionally the;


• radar cross sections(taking into account the aspect angle );


• and the MOF (if tracking is used for plot filtering).

In the case of site acceptance tests the close proximity area shall bechecked thoroughly. If the opportunity traffic does not provide suitable datasample , special test flights shall be used ( the same data sample shall beused for the resolution analysis.)



A.3.3 Resolution.

A.3.3.1 General

According to the EUROCONTROL Radar Surveillance Standard “ theresolution is the capability of the sensor to discriminate between two aircraft inclose proximity and to produce target reports for both . The probability ofdetection is applicable to each individual aircraft.”.

Close proximity is defined for PSR as follows :

• slant range ≤ 2 * nominal (compressed) pulse width;

• azimuth ≤ 3 * nominal 3 dB beamwidth.

It is also specified that “the area in which no resolution capabilities arerequired is defined by a corresponding difference in slant range ∠ 1.5 * nominal(compressed)pulse width and a difference in azimuth ∠ 1.5 * nominal 3 dBbeamwidth.”. The resolution cell of a radar sensor it is defined in range by τ /2(τ ≡ the effective pulse width in meters) and in azimuth by θb (θb ≡ 3dBbeamwidth of the antenna) that means that two targets can not be resolved ifthey lie in the same cell. These areas are shown in Figure A-2 . The diagram isgiving the relative separation - as it is seen by the Radar Sensor - between thetwo aircrafts. The origin O of the axes coincides with the position of one aircraft. The areas are:

• “isolated targets” area is represented by area 3;

• Close proximity area is represented by areas 1, 1a and 2;

• No resolution requirement area is represented by area 1;

• Radar resolution cell is represented by area 1a.

∆ρ (NM) (3)

± 2 τ

± 1.5 τ (2)

±τ (1)

(1a)

O ±θb ± 1.5 θb ± 3 θb ∆θ (Deg.)

Figure A-2

τ = nominal (compressed) pulse width in NM;



τ (NM) =τ (µsec) ∗ c /2 ;

c = velocity of light = 3 x 108 meters/sec=161987 NM/sec

θb = nominal 3 dB beamwidth.


For the technical performance analysis of the radar sensor the datashall be classified in accordance to :

• clutter/interference conditions (ground, sea and weather clutter ).

• the difference between the radar cross sections of the targets (if possible);

• the difference between the Doppler speeds of the target;


For the evaluation of the resolution capabilities of the radar sensorthe probability of position detection for each individual target being in closeproximity shall be estimated. For this the recorded primary and combinedtarget reports at the output of the radar sensor shall at first to be chained, thena reference trajectory shall be reconstructed for each target inside the CMV.The reconstruction of the reference trajectory shall be done as it is describedin par. A.3.2 above. Using this reference trajectory information an algorithmshall sort out all pairs of trajectories having parts falling inside the closeproximity area (Figure A.2 thick line) and then define the parts falling insideareas 1,1a and 2. Then the algorithm shall calculate the number of expectedtarget reports for each part of the trajectory and the total number of expectedtarget reports for each close proximity area. At last using the chaininginformation the number of detected target reports inside the areas 1, 1a and 2shall be calculated.

The probability of position detection Pd shall be estimated for the areas1,1a and 2 using the following formulas:

The number of detected reports chained in close proximity Pd = The number of expected reports in close proximity

(A.3.3)

The Pd inside the close proximity area shall be estimated for theclasses defined in par. A.3.3.2 above.


The results of the analysis shall be presented in a table showing the Pdin each close proximity area for the defined classes of targets.




The results of the resolution analysis may interpreted correctly andbe compared against specified figures (acceptance tests) or measured figures(previous campaigns) if the data sample provides suitable patterns (i.e. targetreports distributed uniformly all over the close proximity area) and the datasample is controlled regarding the :


• radar cross sections(taking into account the aspect angle );


• and the MOF.

For this in site acceptance testing special test flights (see ANNEX D)are considered as mandatory in order to produce a suitable data sample whichcan also be used for accuracy analysis.



A.4 SECONDARY SENSOR DETECTION PERFORMANCE PARAMETERSANALYSIS

A.4.1 General.

The detection performance parameters of a Secondary (SSR) sensorare :

• probability of target position detection;

• probability of code detection;.

• false target reports rate;

• multiple SSR target reports rate.

A.4.2 Probability of target position detection.


For the analysis of the Pd the data shall at first to be classified inaccordance to the distance to neighbouring aircraft. Then the data samplecoming from targets outside the close proximity area (area 4 figure A-9) shallbe classified in accordance to :

• transponder performance taking also into account the aspect angle ;

• environmental conditions (fruits, overinterrogations, TCAS);

• Mode of Flight (MOF)(in case of on site tracking).

Any extrapolated target reports shall be excluded from the calculation.

The justification for the above classification is given by the followingformula A.4.1 . The probability of detection for a Secondary Radar sensor usingsliding window extraction is equal to:

Pd C NN

p p N==∑ − −κ

κ η

κ κ( )1 (A.4.1)

N ≡ number of interrogations ;

η ≡ minimum number of replies to accept a target(criterion to rejectFruits ) ;

p ≡ Pd transponder x Pd radar receiver.

The Pd of the transponder is the probability of replying or the roundreliability.



The Pd of the receiver is the probability of detecting a reply. So theprobability of detection of a SSR depends on :

• the performance of the transponder which is expressed by the Roundreliability;

• the number of interrogators operating near the station (because they mayblock the transponder);

• the flight pattern (if the flight is tangential to the radar the fuselage mayshield the transponder’s antenna);

• the number of Fruit (if there are too many fruits we have to increase thethreshold n).

The above are applicable in the case that the a/c is outside the closeproximity area.

A.4.2.2 Data analysis.

For the estimation of the probability of the target position detection thetarget reports shall at first to be chained. The chaining function shall associateeach target report to and only one trajectory identified by an aircraft number(aircraft identification ) .With this association the number of the expectedtarget reports can be calculated and the gaps due to detection missesidentified .

The Pd measurement shall be Sensor performance based but shalluse multi-radar information where available to detect whether a target ispresent in the CMV of the Radar sensor to be analysed. In a monoradarevaluation the “expected number of target reports“ is taken to be the number ofantenna scans between the first and the last detection of the target. In the caseof special test flights the expected number of target reports equals to thenumber of aircraft Radar Sensor beam encounters.

For the technical performance analysis based on the opportunity trafficthe CMV shall be subdivided in elementary three dimensional cells and the Pdinside each cell shall be estimated. The size of the cell depends on therequired accuracy of the measurement and actually from the number of theexpected target reports inside the cell.The probability of target positiondetection inside a cell shall be calculated using the following formula :

Pd =

The number of detected secondary & combined target reportsThe number of expected secondary & combined target reports

(A.4.2)

The calculation shall not take into account any extrapolated targetreport, false target report or multiple target report.

For the test flights, or individual flights, the probability of detection ofeach point of the trajectory and the average probability shall be calculated.



The calculation of the Pd of a point of a trajectory shall be based on theabove formula (A.8) using a sliding window whose centre is the point of thetrajectory under test see figure A-3 . This shall be called elementary Pdi. The<Pd> (average) of the trajectory shall be calculated by the formula A.4.2.

i = ki = j

Pdk Pdj

Figure A-3

Recommendation The length of the sliding window should be equal to9.

The Pd for the class of data coming from targets lying outside theclose proximity area (area 4 figure A-7) shall at first to be estimated and thenfor the subclasses defined in par A.4.2.1 above

The estimation of the Pd for the targets inside the close proximityarea (areas 1, 2, and 3 figure A-7 ) it is related to the resolution capabilities ofthe radar sensor and it is treated in the relevant paragraph A.5.3.

Recommendation The chaining method should be the ObjectCorrelator currently, under use in RASS tool developed jointly byEUROCONTROL and FAA or equivalent.


The Pd shall be presented in :

• Horizontal polar (for selected Flight levels) and Vertical polar(for selectedazimuthal sectors) diagrams graduated in discrete detection bands such ase.g. 50%, 50-80%, 80-90%, 90-95%, 95-98%, 98-100%;

• Overall Figures (for all the subclasses defined above) derived from themean detection values for each detection cell in the calculation;

• Vertical diagrams These shall be in a form of iso-Pd lines, drawn forselected flight levels;

• Horizontal polar and Vertical polar scattergraphs for the missesgenerated by the chaining process ;

• Distribution of the occurrence and the size of the detection gaps .



An example of the above is given in Figures A-4, A-5, A-6..

The horizontal polar diagrams shall be overlaid on an aeronautical mapof the radar sensor site.


In order that the results of the Pd analysis may be interpreted correctlyand be compared against specified figures (acceptance tests) or measuredfigures (previous campaigns) the data sample shall be strictly controlledregarding mainly the distance to the neighbouring a/c and additionally the :

• transponder performance (including aspect angle);

• the Mode of Flight MOF;

• environment (fruit, overinterrogations, TCAS).



Figure A-4 Horizontal polar diagram (SSR probability of detection)



Figure A-5 Vertical polar diagram (SSR Probability of detection)



Figure A-6 Tabular presentation (SSR probability of detection)



A.4.3 Probability of code detection .


The data shall at first to be classified in accordance to the distance toneighbouring aircraft. Then the data sample coming from targets outside theclose proximity area (area 4 figure A-9) shall be classified in accordance to :



• Mode of Flight (MOF)(in case of on site tracking).

The extrapolated target reports shall be sorted out.

A.4.3.2 Data analysis .

For the estimation of the probability of code detection only the targetreports used for the calculation of the target position detection shall be takeninto account . So only the target reports that the chaining process associate toan aircraft trajectory shall be considered.

The Pcd and Pcv measurement shall be sensor performance based,but shall use multi-radar information, where available, to detect, whether atarget is present in the CMV and whether a code change is due to a pilot actionor to system malfunction.

The probability of Mode A or Mode C code detection for a trajectoryshall be estimated using the following formulas :

P = cd

The number of target reports with validated and correct Mode A

Pcd =The number of target reports with validated and correct Mode C

Mode A

Mode C

The number of detected target reports chained to the trajectory

The number of detected target reports chained to the trajectory

(A.4.3)

N O T E S



1. The code validation of Mode A or Mode C is a process carried out by the Radar sensor under question. The validation is a

flagged ìndication of the correctness of the Mode A/C messagederived from the above process.


For the technical performance analysis of the radar sensor theperformance of the validation process shall be known, so the probability ofcode validation shall be estimated. The probability of Mode A or C codevalidation for a trajectory shall be calculated using the following formula :

=The number of target reports with validated Mode A/CPcv

Mode A/CThe number of detected target reports chained to the trajectory

(A.4.4)

A measure of the efficiency of the validation process is the Probabilityof validating incorrect codes P`cv which is equal to :

P`cv = Pcv - Pcd (A.4.5)

When the analysis is based on the opportunity traffic the CMV shall bedivided in elementary three dimensional cells and the Pcd and Pcv inside eachcell shall be calculated. The size of the cell depends on the required accuracyof the measurement and actually from the number of the expected trajectoriesinside the cell.

The Pcd and Pcv shall be estimated for all the classes defined in par.A.4.3.1 (data coming from targets lying outside the close proximity area figureA-7).

The estimation of the Pcd, Pcv for targets inside the close proximityarea (areas 1, 2, and 3 figure A-7 ) it is related to the resolution capabilities ofthe radar sensor and it is treated in the relevant paragraph A.5.3.

Recommendation. The chaining method should be the ObjectCorrelator currently under use in RASS tool or equivalent.

A.4.3.3 Presentation of the results

For the technical performance the Pcd and Pcv shall be presented in :



• Horizontal polar (for selected Flight Levels) and Vertical polar(forselected azimuthal sectors) graduated in discrete detection bands such ase.g. 50%, 50-80%, 80-90%, 90-95%, 95-98%, 98-100%;

• Overall Figures derived from the mean detection values for each detectioncell in the calculation;

• Vertical diagrams .These shall be in a form of iso-Pd lines, drawn forselected flight levels.

An example of the above is given in Figures A-4, A-5, A-6.

The horizontal polar diagram shall be overlaid on an aeronautical mapof the radar sensor site.

A.4.3.4 Interpretation of results .

In order that the results of the Pcd and Pcv analysis may be interpretedcorrectly and be compared against specified figures (acceptance tests) ormeasured figures (previous campaigns)the data sample shall be controlledregarding mainly the distance to the neighbouring a/c and additionally the :


• environmental conditions (fruit, overinterrogations, TCAS);

• Mode of Flight (MOF).



A.4.4 False / Multiple SSR target reports ratio.


For the technical performance analysis of the radar sensor the datashall be classified in accordance to :


• Mode of Flight;

• distance to neighbouring a/c;

• environmental conditions (Fruits, overinterrogations, TCAS);

• Type of traffic ( civil , military, civil /military ).

The extrapolated target reports shall not be used for the analysis .

A.4.4.2 Data analysis .

For the estimation of the False / Multiple SSR target reports ratio thetarget reports shall at first be chained. As a result chain data shall be derivedwith the history and the characteristics of each target report forming a chain.Then the False /Multiple target reports shall be sorted out based on theparticular characteristics they possess which are generally the following :

a) False SSR target reports

• they are not synchronised ( asynchronous fruits which normally shall notappear at the output of the plot filter);

• they form track with relative short life. (synchronous fruits and second timearound replies );

b) Multiple SSR target reports

• they may have the same A/C code as the real aircraft target reports but theyform track with relative sort life and they appear in certain sectors bounded,by the orientation and the size of reflecting surface. (reflections );

• they appear in pairs with small azimuth separation less than the antennabeamwidth (splits );

• they appear in a ring ,around the radar sensor (sidelobes).

The algorithm shall also correlate the recorded and processed data,with HPD of the antenna of the radar sensor, for the identification of themultiple SSR target reports coming from sidelobes.

The classification of Multiple target reports is made on the basis of range andazimuth separation from a reference target. The diagram below illustrates howthe range and azimuth separation classes associate with each other. Wherethe classes overlap other criteria are used to decide to which class a multiple



target will be assigned, e.g reflections can only be greater in range than thereference target. Although the classes are defined with individual minimum and maximumrange/azimuth limits, in practice several of the boundaries are defined by therange precision and 3dB beamwidth of the system under test.

Radar parameter Value Corresponding FPA classes

ONM 0 Multipath Min Rng Range Precision 1 range quanta Multipath Max Rng , Split Min Rng,

Reflection Minimum Range Antenna Beamwidth 3DB Split Max Az, Reflector Min Az,

Sidelobe Min Az Last expected sidelobe 150 deg Sidelobe Max Az, Backlobe Min Az

Ring Around

Mul'Path

Azimuth separation (degrees)

Split Min Az

Ran

ge s

epar

atio

n (N

M)

Split MaxAz

Multipath Min Rng

SP Max Rng

Sidelobe Min Az Sidelobe Min AzBacklobe Min Az

Backlobe Min Az

SP Min Rng

Multipath Max Rng

Refl Min Rng

Refl Max Rng

Refl Min Az Refl Max Az

AzSplit

O deg

ONM

Side Lobe

Reflections

BackLobeRange/Az

SplitRangeSplit

Figure A-7 Position difference between reference(true) and multiple (false )plot.

The False / Multiple SSR target reports ratio shall be calculated usingthe following formula :

(A.4.5)

RFal/Mul

=The number of False / Multiple SSR target reports The number of detected secondary & combined target reports

(A.4.6)



The number of false SSR target reports (fruit, STAT) a) RFalse= The number of detected secondary & combined targetreports (A.4.7) The number of multiple SSR target reports b) RMulti= The number of detected secondary & combined targetreports (A.4.8) The number of multiple SSR target reports from splits b.1) RSplits= The number of detected secondary & combined targetreports (A.4.9) The number of multiple SSR target reports fromreflections b.2) RRefl.= The number of detected secondary & combined targetreports (A.4.10) The number of multiple SSR target reports fromsidelobes b.3) RSibel.= The number of detected secondary & combined targetreports

In addition to the above an algorithm shall correlate the processed datawith map data and if possible with digital terrain elevation data for theidentification of the reflecting surfaces.

Recommendations.

1) See recommendation of par.7.4.1.

2) False plots due to resolution problem. The resolution case inducedfalse plots are generated due to the radar performance degradation when twoor more aircraft are in a resolution case (inside the close proximity area). Theestimation of this class is straightforward, if the false plot and the reference plotare observed in a resolution case then the multiple is classified as resolutioncase induced false plot and filtered.

2)For the Chaining the Object Correlator algorithm or equivalentshould be applied. For the correlation of the recorded data with digital terrainelevation data RASCAL/SALADT or equivalent should be used. For themeasurement of the antenna diagram RASS_PDP or equivalent shall be used.




In addition to the above on a aeronautical map and on a topographicalordnance survey map of the site of the radar sensor, the position and thenumber of false target reports shall be indicated and the position of thereflecting surfaces .

A.4.4.4 Interpretation of the results.

In order that the results of the False/multiple false targets analysis maybe interpreted correctly and be compared against specified figures(acceptance tests) or measured figures (previous campaigns) the data sampleshall be controlled regarding mainly the distance to neighbouring a/c andadditionally the :


• Mode of Flight MOF ;

• environmental conditions (fruit, overinterrogations, TCAS).



A.5 SECONDARY SENSOR QUALITY PERFORMANCE PARAMETERSANALYSIS

A.5.1 General

The quality performance parameters of a Secondary Radar Sensor(SSR) are:

• Positional accuracy ;

• False code information ;

• Resolution .

A.5.2 Positional accuracy.

A.5.2.1 General

The positional accuracy is defined as “the measure of the differencebetween the position of a target as reported by the sensor and the true positionof the target at the time of detection”. We consider as the true position of thetarget a reference position. This reference position can be extracted eitherfrom data recorded at different input /output (I/O) interfaces of the radar sensorunder test (e.g. .I/O between monopulse receiver and monopulse signalprocessor or I/O between the radar sensor and the Radar Data ProcessingSystem at the centre), or from DGPS positional data recorded on board a testflight aircraft. We assume an error model as follows :

ρ m(t)=(1+κ)*ρ ref (t+δ t)+δρ+σρ (A.5.1)


ρ m = measured slant range

ρ ref = reference slant range

δρ = slant range bias error

σρ = slant range random error

κ = slant range gain error

θm = measured azimuth

θ ref = reference azimuth

δθ = azimuth bias

σθ = azimuth random error

δ t = time stamp error



The time stamping error is only applicable when sensors fusiontechniques are used in the RDPS system.

The error model is based in addition on the assumption that there is arange clock bias error which is represented by the parameter κ.

The bias errors are considered as fixed values corresponding for rangeand azimuth bias to the mean random error.

The accuracy of the reference position shall be at least an order ofmagnitude better than the accuracy of the measured position of the targetreports at the radar sensors output.

According to the EUROCONTROL Radar Surveillance Standardspositional accuracy shall be expressed by the following categories of errors :

• systematic or bias errors ;

• random errors :

• jumps.

The performance for systematic / bias errors shall be expressed by :

• slant range bias ;

• slant range gain error ;

• azimuth bias ;


The performance for random errors shall be expressed by :

• slant range error standard deviation ;

• azimuth error standard deviation .

NOTE- Jumps are target reports with errors in position three times higher ormore than the standard deviation for range and azimuth .


The positional accuracy mainly depends on the signal to noise ratio ofthe reply pulses at receiver output which in turn depends from the transponderperformance. Interrogations from adjacent SSRs may block the transponderand certain flight patterns (tangential ) may shield the transponder’s antenna .The signal to noise ratio is strongly affected if there are other a/c’s in closeproximity . So the data shall at first classified in accordance to the distance tothe neighbouring a/c’s in two major classes :

• data coming from targets in the “isolated targets” area (area 4 figure A-10);



• data coming from targets in close proximity area (areas 1, 2, and 3 FigureA-10).

Then the above classes shall be subdivided in accordance to :


• Mode of Flight MOF;

• environmental conditions (Fruits, overinterrogations, TCAS).


For the estimation of the positional accuracy the recorded data shallat first to be chained. Then a reference trajectory shall be reconstructed foreach target inside the CMV and compared against the measured positions.

The reconstruction of the reference trajectory (for each target inside theCMV) shall be based :

a) on recorded target reports when :


NOTE Position reconstruction can only be reliable when the target is seen bytwo or more sensors . If more than 30% of the chained data are seenby only one sensor then the quality analysis results may be unreliable.

a.2)at least n trajectories can be built with a minimum of m targetreference positions. Where each target reference position shall be within thereference position accuracy stated in par. 6.2.1.

b)on multilevel recordings (e.g. recordings at the video level and at theplot level) when the a.1 and a.2 are not applicable.

c) on DGPS data (coming from test flights) time synchronised with therecorded target reports or any other reference positioning system. The DGPSposition of the target together with the corrected DGPS time should be takenas the reference. The DGPS information will normally be in Latitude/Longitudeand height above Mean Sea Level with coordinates in WGS84. The sensordata will normally be either Range/Azimuth/FL, X/Y local/FL or X/Y System/ FL.The coordinates for the sensors and system origin must be stated in WGS84. To chain the two sources of data and to use the DGPS position as a referenceboth data sources must be projected onto a common coordinate system.Either a Stereographic system (height independent) or a x/y/FL system may beused. In the case of a mono-radar evaluation the system origin should be thesensor site coordinates, i.e. x/y local = x/y system. The GPS altitude values orsensor FL values must also be normalised if errors are to be minimised -correction of Mode C or GPS Altitude values for the regional QNH at the sensorlocation and time of recording would be adequate.



From the comparison of the measured position and the referenceposition for each target inside the CMV and assuming the model A.19 thefollowing errors shall be estimated:

i) systematic (bias) errors :



• azimuth bias;


The systematic errors shall represented by fix numbers.

ii) random errors :


• azimuth error

The random errors shall be expressed by the standard deviation of thedistribution they follow.


The positional jumps shall be expressed by the overall ratio of jumps asfollows :

The number of detected target reportsRj =The total number of jumps

(A.5.2)

The positional accuracy shall be estimated for all the classes andsubclasses defined in par A.5.2.2 above.


a) Object Correlator or equivalent for the chaining and MURATRECor equivalent for the trajectory reconstruction in the case that recordedmultiradar data are available. MURATREC is a curve fitting technique using4th order beta-splines currently under use in RASS tool.

b) RASS-S or equivalent when multilevel recordings are used.


The random errors shall be presented in histograms showing thedistribution they follow figure A-8 is an example of such an evaluation made byRASS-C tool. A quick way to detect sensor’s malfunctions is the use ofscattergraphs as the one in figure A-9 where large errors indicate probablemalfunction of the sensor in this sector.




In order that the results of the positional accuracy analysis may beinterpreted correctly and be compared against specified figures (acceptancetests) or measured figures (previous campaigns) the data sample shall bestrictly controlled regarding first the distance to the neighbouring a/c’s and thenin accordance to :


• the mode of flight;




Figure A-8 Presentation of the range and azimuth errors



Figure A-9 Scattergraph



A.5.3 False code information

A.5.3.1 General

The false code information according to the EUROCONTROLSurveillance Standard shall be expressed by :

• overall false code ratio ;

• validated false Mode A code ratio;

• validated false Mode C code ratio .

N O T E

1. The code validation of Mode A or Mode C is a process carried out bythe Radar sensor under question. The validation is a flaggedìndication of the correctness of the Mode A/C message derived fromthe above process.

2.- Correct means the Mode A/C code value corresponds to the current"correct" value for the associated trajectory. The correct value isdetermined and maintained by the analysis system.


The data shall at first to be classified in accordance to the distance toneighbouring aircraft. Then the data sample coming from targets inside andoutside the close proximity area (see figure A-10) shall be classified inaccordance to :





For the estimation of the false code information only the secondary orcombined target reports used for the calculation of the probability of targetposition detection shall be taken into account . So only the target reports thatthe chaining process shall associate to an aircraft trajectory shall beconsidered.

The measurement shall be sensor performance based but shall usemulti-radar information where available to detect whether a code change is dueto a pilot action or to system malfunction. The false code information shall beestimated using the following formulas :

• for the overall false code ratio



R

Over/f=

The number of reports with incorrect Mode A or/and Mode C (valid or not)The number of detected secondary/combined reports chained to trajectories

(A.5.3)

• for the validated false Mode A codes ratio :

RA f/v

=The number of reports with incorrect and validated Mode A

The number of detected sec/combined reports chained to trajectories

(A.5.4)

• for the validated false Mode C codes ratio :

RC f/v

=The number of reports with incorrect and validated Mode CThe number of detected sec/combined reports chained to trajectories

(A.5.6)

The false code information shall be estimated for all the classes andsubclasses defined in A.5.3.2 above.


The results of the analysis shall be presented in a table showing thefalse code information ratios for each defined class and subclass of data.


In order that the results of the false code information analysis may beinterpreted correctly and be compared against specified figures (acceptancetests) or measured figures (previous campaigns) he data sample shall bestrictly controlled regarding first the distance to the neighbouring a/c’s and thenin accordance to :






A.5.4 Resolution.

A.5.4.1 General

According to the EUROCONTROL Radar Surveillance Standard “ theresolution is the capability of the sensor to discriminate between two aircraft inclose proximity and to produce target reports with correct code for both. Theprobability of position and code detection is applicable to each individualaircraft.”.

Close proximity is defined for SSR as follows :

• slant range ≤ 2 NM;

• azimuth ≤ 2 * nominal 3 dB interrogation beamwidth.

∆ρ (NM)

(4)

±∆ρ2

(2) (1)

±∆ρ1

(3)

O ±∆θ1 ±∆θ2 ∆θ(deg.)

Figure A-10

∆θ 1 2 360= ∗ ∗∗

nf t (A.5.7)

For :

• n (number of SSR interrogation modes) = 2;

• f (interrogation repetition frequency) = 240 Hz;

• t (antenna rotation period ) = 10 sec;

• ∆θ1= 0.6 Deg;

• ∆θ2 = 2 * nominal 3 dB interrogation beamwidth;

• ∆ρ 1 = 0.05 NM;



• ∆ρ 2 = 2 NM.


For the analysis of the resolution capabilities of the radar sensor thedata shall be classified in accordance to :


• Mode of Flight MOF;

• environmental conditions (Fruits, overinterrogations, TCAS).


For the evaluation of the resolution capability of the radar sensor theprobability of position and correct code detection for each individual target shallbe estimated. For this the recorded data shall at first to be chained then areference trajectory shall be reconstructed for each target inside the CMV. Thereconstruction of the reference trajectory shall be done as it is described inpar. A.5.2.3 above. The resolution analysis is based on sections of chainswhich are in ‘close approach state’ - the targets are within a certain mutualseparation from each another.

Before the resolution analysis can take place the test cases must be isolatedfrom the rest of the chained data set. In a multi-radar environment a simpleproximity filter in x/y/time can be used to identify when two targets enter a‘close approach’ state. In a mono-radar case then Range/Azimuth/Time maybe used. The object of the classification is to isolate potentially interesting testcases. Once a number of such cases have been identified then each oneshould be examined to determine if it is suitable for detailed analysis. All of theidentified cases should normally be used for the global analysis of Position andCode information. The detection of close approach cases may use thereference trajectory or any algorithm which has the continuous state of eachtrajectory. Raw sensor data are not suitable for determining mutual separationof targets due to detection failures.

Using this reference trajectory information an algorithm shall first sort out allpairs of trajectories having parts falling inside the close proximity area (FigureA-10 thick line) and then define the parts falling inside areas 1, 2 and 3. Thealgorithm shall calculate the number of expected target reports for each part ofthe trajectory and the total number of expected target reports for each closeproximity area. At last using the chaining information the number of detectedtarget reports inside the areas 1, 2, and 3 shall be calculated.

The probability of position detection Pd and correct code detection Pcdshall be estimated for the areas 1, 2 and 3 using the following formulas:

(A.5.8)

The number of detected reports chained in close proximity Pd= The number of expected reports in close proximity



(A.5.9) The number of reports with correct and valid Mode A Pcd= ModeA The number of detected reports chained in close proximity

(A.5.10)

The number of reports with correct and valid Mode C Pcd= ModeC The number of detected reports chained in close proximity

The probability of position detection Pd and correct code detection shallbe estimated for all the classes defined in par A.5.4.2 above .


The results of the analysis shall be presented in a table showing the Pdand Pcd for each close proximity area and for each defined subclass of data.


The results of the resolution analysis may be interpreted correctly andbe compared against specified figures (acceptance tests) or measured figures(previous campaigns) if the data sample provides suitable patterns (i.e. targetreports distributed all over the close proximity areas) and it is controlledregarding the following :




In the case of site acceptance tests the close proximity areas shall bechecked thoroughly. If the opportunity traffic does not provide suitable datasample, data coming from special test flights shall be used ( the same datasample shall be used for the accuracy analysis.)



A.6 PSR/SSR DATA COMBINING ANALYSIS

A.6.1 General

According to the EUROCONTROL Surveillance Standard PSR/SSRdata combining is the capability of the radar sensor to associate at eachantenna scan the target reports of the same aircraft detected by the twosensors and to combine these reports into a single target report. Thiscapability shall be expressed by the following parameters :

• probability of association (Pas);

• false association rate (Rfas).

An association is considered as false if the target reports from twounrelated targets detected by the two sensors have been associated.

A.6.2 Data classification.

The resolution capabilities of the Primary and Secondary radar sensorsare very different, so the data shall first to be classified in accordance to thedistance to neighbouring aircraft. In this case the close proximity area shall bethe union of the close proximity areas of primary and secondary sensor .Thatmeans that ∆ρ=2NM and ∆θ=3θb where θb is the 3dB beamwidth of theprimary antenna.

Then the data shall be classified in accordance to the :



A.6.3 Data analysis

For the evaluation of the data combining capability of the radar sensorthe probability of association Pas and the false association rate Rfas shall beestimated for the classes of targets defined above.

For the estimation of the overall probability of association and theoverall false association rate the following formulas shall be used :

(A.6.1)

Pas = The number of expected combined reports

Rfas =

The number of detected correct combined reports

The number of detected false combined reportsThe number of detected combined reports (A.6.2)

NOTE Correct / false combined target report is a target report coming fromcorrect / false association of a primary and a secondary target report.



A.6.4 Interpretation of results

The results of the PSR/SSR combining analysis may be interpretedcorrectly and be compared against specified figures (acceptance tests) ormeasured figures (previous campaigns) if the data sample it is controlledregarding the distance to the neighbouring a/c and additional to the following :


• the Mode of Flight MOF.



A.7 ON-SITE DELAY ANALYSIS

A.7.1 General

According to the EUROCONTROL Surveillance Standard the on sitedelay is the time between the moment a radar target for a given aircraft isdetected and the moment when the corresponding report starts to betransmitted. These target reports are polished / filteredprimary/secondary/combined target reports providing measured radar dataafter reduction of false data using mono-radar processing techniques.

A.7.2 Data classification

The processing delay mainly depends on the load of the system so thedata shall be classified in accordance to the load conditions.

A.7.3 Data analysis

To estimate the on site processing delay the time of detection for eachtarget and the time of transmission shall be recorded and their difference shallbe calculated. The recording shall be done at the level of:

• azimuth change pulses (ACP’s);

• video (receiver output);

• plot (plot extractor output);

• and filtered plot (plot combiner output).

The above data shall be time stamped synchronized to a referenceclock preferably GPS. The processing time for each target report (plot/filteredplot) shall be estimated for normal and for overload conditions as well as themean values and standard deviations for the whole data sample .


The results of the on site delay analysis may be interpreted correctlyand be compared against specified figures (acceptance tests) or measuredfigures (previous campaigns) if the data sample it is strictly controlledregarding the load conditions.



A.8 AVAILABILITY ANALYSIS

A.8.1 General

Availability is the probability that a system will be available for use at agiven random time or time interval. The term “available for use “ means that thesystem provides services within the specified limits. The availability is timedepended, and it can be categorised as follows :

• instantaneous availability A(t) which is the probability that the system willbe available at any random time t ;

• mission availability Am(t) which is the probability that the system will beavailable at a time interval ∆t = t2-t1 and it is expressed by the followingformula;

At t

A t dtm

t

t

=−

∫1

2 1 1

2

( ) (A.8.1)

• steady-state availability As(t) which is the probability that the system willbe available for a very large period of time and it is expressed by thefollowing formula :

At

A t dts

t

( ) lim ( )∞ =→ ∞ ∫1

0

(A.8.2)

For systems which are to be operated continuously as a radar systemthe steady state availability shall be measured and from now on will besymbolised by A and will be called simply Availability.

Using theoretical models we can predict the availability of a system.For example for a single system assuming that:

a) the failures and repairs follow exponential distributions;

b) the failure rate of the equipment is known and equals λ;

and c) the repair rate of the equipment is known and equals µ;

the availability is given by the formula :

A =+µ

µ λ(A.8.3)



the availability for a duplicated system in parallel configuration(one system is main the other is stand-by) as in figure A.11 is given by theformula:

Α =+

+ +µ λµ

µ λµ λ

2

2 2

22 2

(A.8.4)

A (λ, µ) B (λ, µ)

Figure A.11

These theoretical models are used during the design phase of asystem for the prediction of the availability of the final product and during theoperational life of the system to improve the availability of the system (e.g. byincreasing the repair rate or decreasing the failure rate or both).

According to EUROCONTROL Surveillance Standard the availability ofthe radar data shall be expressed by the following characteristics:

• maximum outage time due to any given failure fmax;

• cumulative outage time due to all failures over a period of one year atot;

• outage times due to schedule actions s.

The above are illustrated in the figure A.12.

a1 a2 a3 a4 a5 a6 a7

Operating Non-operating s f1 f2 f3 f4 f5 Specified operating time (e.g. one year)

Figure A.12

f ftot i

i

N

==

∑1

(A.8.5)



fmax= max{f1, f2,...,fn} (A.8.6)

For the estimation of the availability of a radar sensor we shall use thefollowing formula ;

A=

Actual operating time x 100

Specified operating time (A.8.7)

or equivalently from figure A.12 :

Α =+ +

=

==

∑

∑∑

a x

a s f

ii

i

i i

ii

1001

7

1

5

1

6 (A.8.8)

NOTE The term “failure” means failure of the sensor to provide data insidethe specified limits and may be caused by a malfunction of thesensor’s hardware, firmware or software.

The MTBF Mean Time Between Failures is defined as the actualoperating time divided by the number of failures as is given by the formula :

MTBF=

Actual operating timeNumber of failures (A.8.9)

or equivalently from figure A.12

MTBFai

i= =∑

1

7

5(A.8.10)

If we assume exponential distribution for the failures then :

MTBF=1/λ (A.8.11)

Reliability R is defined as the probability that the sensor will operatewithin the specified limits and is given by the following formula (if we make thesame assumption as above ):

R e et t

MTBF= =− −λ (A.8.12)

The reliability is called also probability of survival Ps. From the formulaA.8.12 the probability of surviving a period of time equal to MTBF is 0.37 or 37per cent which means that the MTBF should not be considered as a failurefree period.



Recommendation For the estimation of the MTBF the operating timeshould be chosen so as to include at least five failures to give a reasonablemeasure of confidence in the figure derived.

A.8.2 Data analysis

The credibility of the estimation of the availability of a sensor dependsfrom the available time and the failure rate/MTBF of the equipment under test.

The site acceptance tests last normally for a couple of weeks a periodwhich is not sufficient for the measurement of the MTBF of the modernelectronic equipment which have a minimum of around 1000 hours. During thisperiod we can check only for design problems if any under extreme conditions(e.g. maximum/ minimum temperature, supply voltage variances, overloadconditions etc.). This kind of test is called endurance test and depends on theequipment and the time available but it should not last less than 36 hours. Thefailure rate or the equivalent MTBF of an equipment varies during the life timeof the equipment as it is shown in figure A.13 below.

Burn-in Useful life Wearout (I) period (II)(III) λ(t) early chance wearout 1/MTBF failures 0 tb tw t

Figure A.13

Period I is called burn-in period or infant stage and is characterised bya relative high failure rate which decreases rapidly towards a constant.

Period II is called useful life period or operating stage or stable stagewhere the failure rate is essentially constant.

Period III is called wearout period where the failure rate is growingrapidly . The equipment starts to age.

The MTBF of the system can be checked during the warrantee periodof the system which is considered as stable period and normally lasts at leastfor a year. This check shall be repeated regularly during the life time of theequipment. The estimation of the availability of a sensor shall be based on therecorded outage time due to any given failure of the system over a period ofone year.

This can be done either by the sensor’s monitoring and control systemor by an external equipment . We can define “the failure” of the sensor in manydifferent ways depending on the level of sophistication of the monitoring and



control system. One simple way is to define a failure as the non provision oftarget reports including field monitors for more than 2 antenna scans as it isdefined in the EUROCONTROL Surveillance Standard. This definition isbased on the assumption that the monitoring and control system of the sensorwill switch off the sensor if the quality of the provided data is below thespecified level. This is not always the case because the existing monitoringand control systems are checking a very limited number of performanceparameters usually in indirect way.

The monitoring system of the primary sensor usually checks indirectly :

a) the Pd by checking the station parameters which are related to thedetection performance such as :

a.1) in the transmission path:

• power;

• noise figure.

a.2) in the reception path

• receiver sensitivity (using test target at RF level);

• MTI (using moving test target).

b)the alignment error by checking the position of active/passivereflectors.

The monitoring system of the Secondary sensor usually checksindirectly:

a) the Pd by checking :

a1) in the transmission path:

• power.

a2) in the reception path:

• receiver sensitivity using test target.

b)the alignment error by checking the position of the remote field monitor.

At present there is no available external equipment for RTQC(Real TimeQuality Control) (measuring on line all radar sensor performance parameters).

The monitoring of the quality of the radar information is done at the existingsystems by the controller.

So for the existing systems we shall use the above described definition offailure assuming in addition that the monitoring system of the sensor issensitive to changes of the station parameters which have an impact to the



detection and quality performance of the sensor. During the acceptance testingof the sensor the above measurements shall be supported by 24 hours visualobservations of the quality of the radar information by experience controllers.

Recommendation The assessment of the availability of the radar sensorshould be done especially during the acceptance tests either on site by theuse of RASS-S, or at the centre by the use of RASS-C or alternatively theradar data processing system which should take a sample of the radar datafrom each radar sensor connected to the centre.


The results of the availability analysis may be interpreted correctly andbe compared against specified figures (acceptance tests) or measured figures(previous campaigns) if:

• the external conditions are inside the specified limits;

• the tuning and repair of the system is done as prescribed in themanufacturer’s procedures ;

• and the indications of the monitoring and control (if it is used) are related tothe detection and quality performance of the provided radar data .


Edition 0.1 Working Draft Page B/1June 1997

ANNEX B (INFORMATIVE)

RADAR SENSOR DETAILED TECHNICAL PERFORMANCE ANALYSIS

B.1 General

The detailed technical performance analysis is applied during factoryand site acceptance tests and after major repair or modifications during the lifetime of the radar sensor. In the detailed technical analysis the performance ofthe individual equipments composing the radar chain is assessed. Figure B.1is a generic functional diagram which covers most different system designsand shows the different input / output interfaces which can be used for thedetailed technical analysis of the radar sensor. Modern integrated systemsmay present practical problems for making measurements at certaininterfaces. For example, a recent trend in surveillance systems is to integrateon site tracking which gives raise to the surveillance processing plotcombination and data transmission functions being combined into one systemelement. That makes it difficult or impossible to access the interfaces PIO6,SIO6, CIO1 and CIO2 without highly specialized interface equipment. In orderto avoid this kind of situation, manufacturers of equipment should be urged toprovide, as much as possible, easily accessible interfaces.

B.1.1 Input/output (I/O) interfaces.

Reference is made to Figure B.1 and in particular to the I/O interfacesdesignated:

• PIO for I/O interfaces related to the primary radar element;

• SIO for I/O interfaces related to the SSR element;

• CIO for common I/O interfaces at radar sensor site level.

In Figure B.1 the I/O interfaces are shown by a common designation.Although the input and output Interfaces may well be common points (i.e. aconnector, a data bus etc.) they may be physically separated. For the sake ofconvenience and simplicity, an input or output interface at a certain point withina system (e.g. receiver output) has been given a common designation (e.g.PIO2 and SIO3, etc.).

B.1.2 Output interfaces

The output interfaces are points in the radar system where data can beoutput, either in analogue or digital form for:

a) analysis in a radar analysis tool;

b) standard measurements using normal test equipment (oscilloscopeetc.);

and c) recording.


Page B/2 Working Draft Edition 0.1June 1997

B.1.3 Input interfaces

The input interfaces are points in the radar system where data can beinjected either in analogue or digital form in order to test the system particularlyfor special cases including performance anomalies. The injected signal/datamay be either analogue or digitally synthesized (simulated) or in the form of arecorded message.

B.1.4 Primary radar I/O interfaces

a) PIOl: Radiated RF input

This is the radiated RF input to the PSR system and a test input will typicallybe from an active reflector. This is an input-only interface.

b) PIO2: Primary radar RF input interface

At this point RF tests signals can be injected into the input port(s) of the PSRreceiver(s). This is also an input-only interface.

c) PIO3: PSR video (analogue or digital) input/output interface

This point represents the output of the PSR receiver(s) where detected videocan be output for recording purposes. Similarly, this point acts as an inputinterface for the injection of synthetic (simulated or recorded) video. Accordingto PSR system philosophy, the video at this level may be either analogue ordigital (quantized).

d) PIO4: Primary radar processed video I/O interface

This I/O interface represents the output of the PSR intermediate videoprocessing of the primary radar system. The video at this point will have beensubjected to processes such as MTI, MTD, CFAR, LogFTC in order to obtainusable data (analogue or digitized) for input to the primary plot extractor. At thispoint data can be either injected (tests, simulations, etc.) or extracted(recordings etc.).

e) PIO5: Primary radar extractor video (plots) I/O interface

This I/O interface represents the output of the primary plot extractor and thedata is entirely in digitized form. As in the other cases, data can either beinjected or extracted according to the task to be carried out.

f) PIO6: Primary radar track/filtered plot I/O interface

At this point, the extracted PSR plots have been subjected to a further rotation



Figure B.1 I/O Interfaces



scan to scan processing in order to eliminate false plots, and possibly to formmonoradar tracks. As in the other cases data can either be injected orextracted at this point according to the task to be carried out.

g) PIO7: Primary radar transmitter output

This is an output-only interface.

h) PIO8: Primary timing unit

In most cases, this is an output-only interface.

NOTE.- In modern architecture systems several intefaces operate together( e.g. PlO5, PlO6, SIO5, and ClO2, on a local area network (LAN)).

B.1.5 Secondary radar I/O interfaces

a) SIO1: Radiated RF input

This is the radiated RF input to the SSR system and a test input will typicallybe from a remote field (or site) monitor. This is an input-only interface.

b) SIO2: Secondary radar RF input interface

At this point, RF test signals can be injected into the input port(s) of thereceiver(s). This is also an input-only interface.

c) SIO3: SSR video (analogue or digital) I/O interface

This point represents the output of the SSR receiver(s) where detected videocan be output for recording purposes. Similarly, the point acts as an inputinterface for the injection of synthetic (simulated or recorded) video. Accordingto SSR system philosophy, the video at this level may be either analogue ordigital (quantized).

d) SIO4: Secondary radar processed video I/O interface

This I/O interface represents the output of the SSR intermediate videoprocessing of the secondary radar system. At this level the video(s) may havebeen subjected to such processes as:

• RSLS processing;

• OBA processing; and

• Video reconstitution.

The data at this point may be either in analogue or digital form and provides thenecessary input to the secondary plot extractor. It should be noted howeverthat in modern SSR equipment (particularly for monopulse SSR applications),the receiver, intermediate video processing and plot extractor may be onecommon unit, making it more difficult for accessing data (video/plots) at this



level. At this point, data can be either injected (tests, simulations etc.) orextracted (recordings etc.).

e) SIO5: Secondary radar extracted video (plots) I/O interface

This I/O interface represents the output of the secondary plot extractor and thedata is entirely in digitized form. As in the other cases, data can either beinjected or extracted according to the task to be carried out.

f) SIO6 Secondary radar surveillance processor plot/track I/O interface

At this point, the extracted SSR plots have been subjected to a furtherprocessing in order to eliminate false plots, and in some instances formmonoradar tracks. As in the other cases, data can either be injected orextracted at this point according to the task to be carried out.

g) SIO7: Secondary radar transmitter output

This is an output-only interface.

h) SIO8: Secondary timing unit

In many cases this unit may have an additional input for external (e.g. primaryradar) synchronization.

B.1.6 Common radar I/O interfaces

a) CIO1: Plot combiner I/O interface

At this point, the extracted PSR and SSR data have been subjected to certaincombination criteria and the output at CIO1 will consist of:

• combined plots/tracks;

• SSR-only plots/tracks;

• PSR-only plots/tracks.

In the case that the radar station is PSR or SSR-only, no plot combiner will berequired.

b) CIO2: Combined surveillance processor I/O interface

This is a special case of the PIO6 and SIO6 I/O Interfaces and corresponds toa system where no separate PSR and/or SSR surveillance processing iscarried out before plot combination. As in the other cases, data can either beinjected or extracted at this point according to the task to be carried out.

c) CIO3: Modulated transmitter data

This interface is suited for analogue data recording.

d) CIO4: output of transmission medium



At this point, however, the modulated data from the transmitter containingpossible errors due to additional noise from the transmission line and otherdistortions, can be analysed.

B.2 Analysis application

The detailed technical performance analysis should be applied during:

• factory acceptance tests;

• site acceptance tests;

• commissioning ;

• post modifications.

The characteristics of the equipments forming the radar chain(e.g.antenna, transmitter, receiver) that can be measured depend on the availableinfrastructure and test equipments. So some of the parameters can bemeasured only in the factory during the factory acceptance tests. The followingparagraphs give a very limited information for the measurements in the factoryand some guidelines for the on site measurements.

B.3 Antenna performance analysis

B.3.1 General

The antenna performance analysis is usually dealing with the followingantenna characteristics:

a) antenna gain ;

b) antenna polar diagrams (horizontal and vertical);

c) azimuth squint and skew;

d) cross-polarization, ellipticity ratio, ICR (integrated cancellation ratio);

B.3.2 Test method

a)Gain.

The gain measurement is made during factory acceptance tests usingspecial test sites and special test equipment and on site using special testequipment while the radar sensor is in operation. The measure-ment of thegain shall be made at the peak of the beam and shall be used for thecalibration of the horizontal and vertical polar diagrams. During the on site testsonly the gain of the antenna for the horizontal plane passing from the probeantenna is measured. The SIO1 and PIO1 interfaces shall be used when thesystem is in operation (regular checks). The SIO2 and PIO2 interfaces shall beused in the factory acceptance and site acceptance tests. The gainmeasurement requires a special calibrated gain antenna (usually a horn or aYagi) and receiver.



b) Horizontal and vertical polar diagrams

The horizontal polar diagram can be measured simultaneously with thegain during factory and on site tests. The vertical polar diagram normally canbe measured at the manufacturer’s test site .On site measurement can bemade for the SSR antenna using opportunity traffic and for the PSR antennasolar measurements. An indirect way, during site acceptance tests, is todeduct the VPD from the data collected during test flight for the verticalcoverage .

c)Azimuth squint and skew

The azimuth squint and skew is the variation in azimuth and elevationof the peak of the beam with respect to the mechanical elevation of theantenna. This characteristic can be measured only during factory acceptancetests using test sites and special test equipments.

d)Cross-polarization, ellipticity ratio, Intergrated CancellationRatio

Cross polarization is the polarization component orthogonal to a referencepolarization (i.e. for the SSR the reference polarization is vertical ). So for theSSR the cross polarization is the horizontal component of the field vector (inideal situation this component should be zero). The cross polarization can bemeasured using two calibrated antennas (linear polarized) with orthogonalpolarization planes. This measurement can be made during the factoryacceptance tests or site acceptance tests.

Ellipticity ratio and integrated cancellation ratio are equivalent terms and can beinterchanged. These characteristics can be measured only in the factoryduring factory acceptance tests.

B.3.3 Presentation of results

The results shall be presented in form of diagrams giving the antennagain with respect to azimuth and elevation angles. Figure B.2 is a typicalexample of horizontal polar diagram.

B.3.4 Interpretation of results

The results shall be compared against specified values duringacceptance tests and against previous measurements during regular tests.



Figure B.2 Horizontal polar diagram

B.4 Transmitter performance analysis

B.4.1 General

The transmitter performance analysis is usually dealing with thefollowing transmitter characteristics:

a) output power;

b) power spectrum;

c) pulse characteristics/spacing.

For the measurement of the above characteristics the PIO7 and SIO7interfaces shall be used.

B.4.2 Test method

a) output power

The output power can be measured either as an average or as a peakvalue using one of the following equipments:

• average power meter;

• peak power meter;

• spectrum analyser;

• single-shot digitising oscilloscope;

• repetitive digitizing oscilloscope.

b) power spectrum



A sample of the RF signal shall be checked for bandwidth , sidelobelevel, and level of harmonics using a spectrum analyser. For SSR theBandwidth shall be check for compliance with ICAO Annex 10 specifications.Programmable spectrum analysers can measure at the same time thefollowing characteristics:

• carrier frequency;

• pulse repetition frequency and pulse width;

• duty cycle;

• peak power;

• average power.

c) pulse characteristics/spacing

The pulse characteristics shall be measured using an oscilloscope orspectrum analyser (for the SSR the pulse spacing shall be measured inaddition)and are the following:

• rise time;

• fall time;

• duration;

• pulse repetition frequency;

• pulse stability (phase and amplitude especially for PSR).

For the SSR the pulse space /spacing shall be checked for compliancewith the specified figures in Annex 10.


Not applicable.


The results shall be compared to the specified figures duringacceptance tests and previous measurements during regular tests.

B.5 Receiver/video processing performance analysis

B.5.1 General

The receiver/video processing performance analysis is dealing with thefollowing characteristics:

• losses;



• STC/GTC;

• noise figure;

• bandwidth;

• Off boresigth angle (OBA);

• dynamic range;

• minimum detectable signal MDS;

• filter response, improvement factor.

B.5.2 Test method

a) losses

The losses shall be measured using a vector network analyserconnected to the PIO2 and SIO2 interfaces.

b) STC/GTC

In the primary sensors the gain control is applied at the RF and /or IFlevel and is derived usually from ground clutter maps. In the secondarysensors the STC is applied at the video level. For the PSR STC/GTCmeasurement a rf test pulse shall be injected (a signal generator shall beconnected at the PIO2 interface) when the system is in operation and thesignal strength shall be recorded at the PIO4 interface. For the SSR STC/GTCmeasurement a video test pulse shall be injected (a signal generator shall beconnected at the SIO3 interface) and the signal level shall be recorded at theSIO4 interface.

c) noise figure

For the measurement of the noise figure a wide-band noise sourceshall be connected at the PIO2 and SIO2 interfaces. The noise power at thePI03 and SIO3 shall be recorded with noise source off. Then the noise sourceshall switched on and the output shall increased so as the noise power atreceiver’s output is doubled.

d) bandwidth

For the measurement of the bandwidth of the receiver a c-w signalgenerator shall be connected at PIO2 and SIO2 and the spectrum shall berecorded at the PIO3 and SIO3 interfaces using a spectrum analyser. For theSSR the measurement shall be compared against the specified figures inANNEX 10.

e) Off Boresigth Angle (OBA)

This measurement is applicable to Monopulse SSR systems only. TheOBA is measured at SIO3 . BITE or test sets shall inject test signals at SIO2.



The error pattern is measured as the ratio of the log Sum pattern to theDifference pattern.

f) Dynamic range

For the measurement of the dynamic range of the receiver a rf testpulse shall be injected at PIO2 and SIO2 . The rf test pulse shall be increasedslowly until the signal at the PIO4 and SIO4 reaches its saturation point.

g) Minimum Detectable Signal (MDS)

The MDS is defined either for 0db Signal to Noise at the output of thereceiver and then it is called tangential sensitivity or for 3db S/N. The set up isas for the dynamic range and the MDS is the power for which S/N at the outputis either 0db or 3db.

h) filter response(MTI, MTD) Improvement factor.

This measurement is applicable to PSR only. The MTI, MTD Filterresponse shall be fully investigated over the radial speed range specified forthe system. The rf test pulse generator shall produce test pulses with variousamplitudes and phases with respect to the transmitted pulse. The zero velocityfilter shall also be checked during site acceptance tests with use of a testaircraft flying a circular pattern around the radar at a constant height. Theimprovement factor I is defined as the ratio of the Signal to Clutter at the inputof the filter to the Signal to Clutter at the output.

IS CS C

o

i=

( / )( / )

The improvement factor is measured usually during factory acceptancetests using simulated data ,but it can be measured on site (using the aboveformula) by injecting an rf pulse over a ground and or sea clutter area.


The results shall be presented in an appropriate form e.g. attenuationversus range for STC/GTC, or Gain versus Doppler speed/frequency for MTIfilter response.

B.5.4 Iterpretation of results

The results shall be compared against the specified values or previousmeasurements.

B.6 Plot extractor performance analysis

B.6.1 General

The plot extractor performance analysis is usually dealing with thefollowing characteristics :



• Constant False Alarm Rate (CFAR) performance;

• extraction criteria;

• correlation interpolation;

• defruiting function;

• code detection/validation;

• resolution.

B.6.2 Test method

a) Constant False Alarm Rate (CFAR ) performance

This characteristic is applicable only to PSR and can be measuredduring Factory acceptance tests. Using a “hit pattern “ generator simulating aclutter hit pattern connected at PIO4 we can measure at the output (PIO5) thenumber of false plots produced. By moving a test target inside the clutter areawe can measure the CFAR losses.

b)extraction criteria

With the same test set up as above the leading and trailing edgecriteria can be tested.

c) correlation interpolation

With the same test set up the performance of the plot extractor tointerpolate the position of the target in the presence of noise /clutter can bechecked. At the output the recorded position of the test target is checkedagainst the expected one.

d) defruiting

This is applicable to SSR and can be checked using a special replygenerator connected at SIO4. At the output SIO5 the number of false plotscreated by the injected FRUITS (asynchronous replies) shall be counted.

e) code detection / validation

The code detection / validation can be checked using as above a replygenerator or using live traffic as described in Annex A above.

f) resolution

The resolution can be check either using test targets or live data asdescribed in Annex A above.


Not applicable.




The results shall be compared against specified values or previousmeasurements.

B.7 Plot filter performance analysis.

B.7.1 General

The aim of the plot filter is to reduce the number of false plots withoutaffecting the probability of detection . The majority of the plot filters are usingtracking. For the PSR sources of the false plots are the following:

• Moving clutter (sea, weather angel);

• ships and cars;

• interference.

For the SSR the sources of false plots are the following:

• reflections;

• sidelobes;

• splits.

Another characteristic which shall be checked is the reaction of thesystem to overload conditions.

B.7.2 Test method

The performance of the plot filter can be checked using live traffic dataand making recordings at the input PIO5/SIO5 and at the output PIO6/SIO6 orCIO1 as described in Annex A above. The overload reaction can be checkedusing a plot simulator .


Not applicable.


The results shall be compared against specified figures or previousmeasurements.


Edition 0.1 Working Draft Page C/1 June 1997

ANNEX C ( RECOMMENDED)

FLIGHT TESTING METHODS

C.1 General .

The radar sensor performance analysis shall be based on recorded data,coming from opportunity traffic. Special test flights shall be used, only in thefollowing cases :

• when the performance parameters analysis requires special aircraft confi-gurations ( e. g resolution check );

• during the site acceptance tests ;

• during the site commissioning of the radar sensor ,if there is no adequateopportunity traffic .

Flight testing shall use small aircraft, equipped with an approved transponder,for all radar flight tests. Small aircraft are considered to be the BeechcraftBonanza, Cessna 182, and other aircraft of similar size which represent nearlythe same reflecting surface. The Sabreliner, Jet Commander, Jetstar and otherjets of similar size are also regarded as small aircraft for the purpose of radarflight checks. Aircraft selection should consider possible limitations due toaircraft range, terrain, weather conditions, etc. The flight testing aircraft shallcarry a calibrated transponder for SSR power optimization and GTC curveestablishment. Flight test aircraft shall provide the pilot selection of any one ofthe following three combinations of power output and sensitivity :

• 350 ±50 W power output and 75 ±1 dbm sensitivity. (Normal/Normal);

• 350 ±50 W power output and 69 ±1 dbm sensitivity. (Normal/Low);

• 80 ±20 W power output and 69 ±1 dbm sensitivity. (Low/Low);

C.2 Flight testing procedure

C.2.1 Introduction

A Radar flight testing may be a single (special inspection) requirement to de-termine coverage over a new air traffic "fix" or may consist of a full radarcommissioning . The number of personnel, coordination, preparation, andreporting involved between the two extremes varies widely. A commissioningflight test (or a special test following significant modifications to existingequipment) consists of three distinct parts; planning, engineering, anddocumentation. The engineering, or equipment, portion includes the testsnecessary to ensure that the radar sensor performs according to designspecification. Some test in the engineering phase should require a flight testaircraft. The documentation or flight test portion determines to what extent the


Page C/2 Working Draft Edition 0.1 June 1997

operational requirements are met and establishes a radar coverage baseline.The operational requirements should be outlined in the radar sensor sitting andflight testing plan. The detailed procedures covered are devoted primarily to theflight testing phase.

C.2.2 Commissioning .

The objective of the commissioning is to evaluate system performance,determine and document the site coverage, and provide a baseline for thedetection of future deterioration in equipment performance. Data obtainedduring this test shall be used as a basis for periodic comparison of radarsensor performance as well as subsequent tests. Major events ofcommissioning include:

• planning (develop technical plan);

• measure radar sensor performance parameters;

• equipment Optimisation;

• site Integration;

• flight testing (data collection & analysis);

• presentation of results;

• generate a database (baseline).

C.2.3 Special tests

Special tests are conducted to fulfil a particular need and may be very limited inscope. The following is an example of testing events:

• develop a starting baseline (as found);

• identify problem areas (quantity, if possible);

• correct the problem or recommend solutions;

• review performance;

• generate a new database.

If equipment changes/modifications to commissioned sensor change thecoverage pattern, document the changes in the test report. The new coveragepattern shall then become the basis for comparison during subsequent tests.Special tests include the following:

C.2.3.1 Antenna Change.



The checklist, Table D1, indicates the requirements for installation of a newantenna, a new generation multiple beam antenna, or an antenna with adifferent radiation pattern. A flight test is not required following an antennapedestal or rotary joint replacement if the ground measurements of thereflector position, feedhorn alignment, and antenna tilt of the replacementpedestal are satisfactory.

C.2.3.2 Major Modifications (other than antenna change).

This test should be confined to the parameters necessary to confirm sensorsperformance. The radar engineer shall determine the extent of a special testduring preparation and coordination of the plan. Depending upon the extent ofthe modification, an analysis using radar analysis tools and targets ofopportunity may satisfy the requirements.

C.3 Checklist

The tests required to complete a full commissioning flight test are contained intable C-1. The procedures presented here are also those to be used singlywhen the requirements for a special test may be satisfied with one or more ofthe individual tests. Those items identified with an "x" are mandatory.Engineering personnel shall evaluate the data obtained using targets ofopportunity to determine if further evaluation by a special flight test aircraft isneeded. The column labelled "transponder mode" denotes the proper aircrafttransponder configuration for the specific test.

Commis sioning

PSR/SSR AntennaChange

PSR SSR Check same differ. same differ. transponder

Orientation x x x x x norm./norm. Tilt x x x x x norm./norm. PSR optimization• STC / GTC• Beam crossover• false target optimization

x x x x

x x x x x

norm./norm. >> >> >>

SSR optimization• power• SLS/ISLS• Modes/Codes• GTC/STC Establishment

x x x x x

x x x x

x x x x x

low/low norm./low norm./low low/low low/low

PSR/SSR Integrity x x x norm./norm. Vertical Coverage x x x low/low Horizontal screening o x x norm./norm. Airways/Route coverage x x x low/ low standby equipment x >> standby power x norm./norm.

Table C-1 Test Checklist



x denotes mandatory test

o optional - at engineering/maintenance/controller request.

C.4 Vertical Coverage/Operational Capability

C.4.1 Background

The purpose of this test is to determine and document the primary andsecondary radar sensor vertical coverage. The primary and secondary radarcoverage within the fringe envelope shall be evaluated using Radar analysistools, opportunity traffic, cooperating aircraft, or flight test aircraft. Radar datarecordings and analysis of the vertical coverage test are used as a continuingdatabase for a permanent record, and as a legal document certifying sensorsperformance.

C.4.2 Vertical Coverage Radial

The test shall be conducted on reference bearings from the radar site. Thecommissioning and all subsequent tests concerning sensors performanceshall be conducted on the same bearings for valid comparison.. One radialshall be free of clutter, dense traffic and populated areas, and influencescreated by line-of-site. If the CMV includes ground/sea clutter areas at leastone radial shall be flown over these areas.

C.4.3 Commissioning Procedure

The outer fringe shall be determined by evaluating tail-on targets and the innerfringe by nose-on targets. Aircraft reflective surface and transponder antennacharacteristics vary between inbound and outbound flight;consequently, somedifference in coverage can be expected. Map checkpoints, a navigation systemradial, or radar vectors shall be used to remain on vertical coverage radial. Allpattern altitudes described herein shall be flown as height above the radarantenna.

NOTE -In order to produce a meaningful database, the flight test a/c must flytrue altitudes (corrected for pressure and temperature).

C.4.3.1 Commissioning Profile

Refer to Figure C1 and proceed as follows:

C.4.3.1.1 Fringe Envelope Check. The flight test a/c shall fly outbound from the site at1,000 ft above the antenna to the outer fringe, up to the outer fringe to therequired altitude, across the top inbound to the inner fringe, then down the innerfringe to the 1,000 ft inner fringe. Probe and score the primary and secondaryfringes at 1, 2, 3, 5, 7, 10, 15, 20, 25, and 30 (as required) thousand ft.Establish the ascending (outer) fringes by turning inbound and climbing to thenext higher level, flying inbound at the higher level until solid primary andsecondary reports are received, then turning outbound to establish the primary



and secondary at that level. Evaluate the inner fringes in the same manner,with the directions reversed. Conduct the over-all-quality and auxiliary functionstest at 5,000 ft or 30,000 ft per the previous procedures.

C.4.3.1.2 Coverage Within the Fringe Envelope. Engineering personnel shall useradar analysis tools and targets of opportunity to determine the coverage insidethe fringe envelope, and identify the location and extent of holes and otherlobing related anomalies. Coverage can be determined with analysis plots onseries of recording. Limit the target reports to a 20° wedge, centred on thevertical coverage azimuth and filtered for the altitudes of concern. The SSRdelay should be active during the recordings, to provide a better separation ofprimary and secondary target reports for independent analysis. Lobing will beevident as primary and secondary target reports, exhibiting decreasing runlengths as they enter a "hole", disappear in the null, then reappear withprogressively higher run lengths as they clear the ringe on the opposite side.Include the printout plots in the facility permanent database.

NOTE- "SSR delay" refers to the technique of delaying the SSR signal beyondthe association window of the plot filter combiner.

Fig. C.1 Commissioning profile

C.4.4 PSR Antenna Change

When the PSR antenna is changed, fly the profile depicted in Figure C 2A .



a) Repeat the outer fringe checks a necessary in order to complete an overall-quality and auxiliary functions tests as requested by engineering personnel.Conduct the remainder of the coverage check in the original configuration.

b) Checks of additional sensors equipment configurations and additionalaltitudes may be conducted at the option of engineering personnel.

C.4.5 SSR Antenna Change

For the same type of antenna, all requirements may be completed usingtargets of opportunity. Comparison analysis is performed on the historic solardata, SSR parameters, and performance measurements (targets ofopportunity) to ensure the same performance (commissioned) can beexpected with new antenna. When the antenna is replaced with different type,or targets of opportunity are not available, checklist requirements shall becompleted using a flight testing aircraft.

a) Terminal SSR. Fly the profile for a primary antenna change as illustrated inFigure C 2A.

b) En-route SSR. Fly the profile for a primary antenna change as illustrated inFigure C 2B.

Fig.C.2 Terminal SSR (a) En-Route SSR (b)

C.5 Horizontal Screening



Horizontal screening shall be determined by running the radar analysisprograms on pre-recorded data. Limit the data input on successive runs toazimuth sectors with a constant screening angle for each run. Compute thescreening angle for any given run (azimuth sector) from the lowest coveragereturns at a given range. Then, coverage at any given range beyond the screencan be predicted and a comparison drawn between values on the horizontalscreening chart of actual coverage. Limit tests to elevation angles near theexpected horizon.In the case that there are no opportunity traffic and dependingupon local requirements, horizontal screening shall be accomplished by thefollowing method:

Using either flight test or rental aircraft, fly an orbit at an altitude and distancewhich corresponds to the lowest screening angle at which coverage isexpected. Orbit radius of less than ten nautical miles shall not be used. DME orheadings provided by the controller may be used to maintain the orbit. Select"Normal" on the aircraft transponder. MTI, if used, shall be gated to a rangeinside the orbit radius, except those locations where ground clutter will obscurethe target unless MTI is used. If MTI must be gated outside of the orbit, theradius of the orbit should be constantly changed to avoid target cancellationdue to tangential blind speed. For example, vary the pattern on a 12 NM orbitbetween 10 and 14 NM so as to average a 12 NM orbit.

C.6 Airway/Route Coverage

The airway coverage shall be checked using radar analysis programs andtargets of opportunity. Targets may consist of one cooperating aircraft or aassortment of aircraft reports on a particular airway: Targets included in theoutput data shall be Mode C or S equipped for essential altitude information.Scoring may be accomplished either with radar analysis programs ormanually. Document fix positional coverage by filtering a data run with thestart/stop azimuth and high/low altitude that effectively "boxes" in the fix. Goodcoverage within the box constitutes adequate coverage at the position fix.In thecase that there is no enough opportunity traffic the check shall be executedwith the following method:

Select "low" on the Flight test/rental aircraft transponder. Configured theprimary radar in circular polarization. Fly the minimum coverage altitude notlower than the Minimum Obstruction Clearance Altitude (MOCA), on airwaycentreline. Maintain course guidance by reference to ground checkpoints,navigation system signals, or radar vectors. Fly terminal arrival/departureroutes and other areas of interest identified in the flight test, via radar vectors atthe minimum obstruction clearance altitude.

C.7 Standby Equipment

The purpose of this test is to evaluate the performance of standby equipment,and may be accomplished during pre-flight testing using targets of opportunity.Some radars have been engineered to meet reliability requirements throughthe use of redundant parallel units. Structure the pre-flight testing of thesesystems so as to thoroughly test all such redundant units. A standby antenna



(duplicate) may be installed at selected locations to provide for continued radarservice in the event of antenna failure. The commissioning requirements for astandby antenna may be completed using the antenna checklist.

C.8 Standby Power

The purpose of this test is to evaluate radar performance on standby (enginegenerator or UPS -Uninterruptable Power Supply-) power and shall beconducted during pre-flight testing. Results are satisfactory when the enginegenerator monitor equipment detects a power without manual intervention.Conduct this test with a simulated power failure by manually switching out theincoming commercial power.

C.9 Analysis

C.9.1 Testing Precautions

Any system deficiency or deterioration noted during inspection shall beinvestigated. When a system parameter does not meet the specifiedtolerances and cannot be adjusted within a reasonable length of time, the flightshall be discontinued until the discrepancy can be resolved. However, thisdoes not preclude the continuation of testing, in an effort to resolve theproblem.

Recommendation For the s i t e commissioning of the radar sensordata should be collected under all seasonal conditions and if applicable ,alsounder anomalous-propagation.

C.9.2 Evaluation

Continuous radar detection (one usable target report on every scan at everyazimuth and all altitudes) is a difficult requirement to meet due to antennalobing, physical limitations (line-of-sight), aircraft altitude, and antenna tilt.Therefore, expect isolated or non-recurring misses. After three or moreconsecutive misses in the radar pattern, investigate to determine whether ahole exists and, if so, its size. Reference is made to Figure C4

C.9.3 Lobing

Lobing is caused by the summation of radar energy at a point in space. Theenergy components at that point may consist of both direct and reflectedenergy. As the reflected and direct path lengths to that point differ, the twosignals arrive with a different phase relationship. With an opposite phase froma strong reflection, the out-of-phase component may cancel the direct,resulting in a coverage hole. As reflected energy is the source of all lobingproblems, preventing or altering the reflected energy component is the way tominimize the problem. Lobing in a critical area can occasionally be reduced,but usually at the expense of performance in other areas.



Adjustments to the antenna tilt (primary and secondary) and secondarytransmit power are the two most effective measures in combating nulls. Usecare in making tilt and power changes, since either can introduce additionalproblems. Optimizing antenna tilt and reducing the ground radiation may be allthat is required to reduce a lobing problem.

Fig.C.3 Lobing

C.9.4 Probing

Holes in radar detection are probed in similar manner to VOR or TACAN. Thefollowing procedures may be used a guide, refer to Figure C4.

C.9.4.1 Horizontal. Fly through the area in question to determine the inner and outerlimits of the hole. Vary aircraft position by 10° of radar azimuth until the laterallimits of the hole are determine.

C.9.4.2 Vertical. Fly through the centre of the pattern (established in the horizontalprobing procedure) at 1,000 ft increments to determine the upper and lowerlimits of the pattern.



Fig.C.4 Vertical and horizontal probing

C.10 Documentation.

The Flight test report shall consists of a detailed accounting of allcoverage data obtained using participating and flight test aircraft, targets ofopportunity, radar analysis tools, and all flight test reports.


Edition 0.1 Working Draft Page D/1 June 1997

ANNEX D ( RECOMENDED)

METHODS TO ASSES THE RESOLUTION CAPABILITIES OF RADAR SENSOR

D.1 General.

The assessment of the resolution capabilities of sensor systems forms part ofthe performance assessment for reliability and quality.

Resolution has an impact on the probability of position (PSR and SSR) andcode (SSR) detection when two aircraft are in close proximity:

i) PSR, see paragraph A.2.2.2.

ii) SSR, see paragraph A.4.2.3.

Resolution has an impact on the quality of position data (PSR and SSR) andfalse code detection when two aircraft are in close proximity:

i) PSR, see paragraph 6.3 and A.3.3.

ii) SSR, see paragraph 8.4 and A.5.4.

D.2 Circumstances of testing.

Resolution can be tested during the different periods of the life cycle of asensor system. One of the following methods can be applied whereby thecircumstances of testing have been taken into consideration:

Purpose oftest

Simu-lateddata

Combinationof live andsimulateddata

Live data fromtesttransponders

Live datafrom trafficofopportunity

Live data fromtest flights with(optional)support ofDGPS data

FAT yes SAT yes yes yes yes yes Annualperformanceevaluation

yes yes

RTQC yes STCA yes yes RSS yes yes

D.2.1 Simulated data.

Simulated data can be categorised according to the sophistication of testing:

• outside the antenna as environmental data;


Page D/2 Working Draft Edition 0.1 June 1997

The antenna shall be turning and the data are generated from a single test sitefor range resolution testing and from a fixed test site in combination with amobile site for range and azimuth resolution. Attention shall be paid to theelevation angle of the test sites.

• insertion at rf level through rf coupler(s);

Insertion of simulated data at rf level through an rf coupler in the cable path tothe antenna. The scenarios for the simulation are programmable and may betypical or specific. One or more rf units can be used whereby each of the unitscan play the roll of one target. The triggering of the individual units can be madesynchronous or asynchronous to the radar.In the case of monopulse all threechannels shall be generated.The scenarios for testing can be derived frompure test scenarios, from video during replay of recorded video, from externalscenarios lproduced by SMART or ODIT.

D.2.2 Combination of live and simulated data

Combination of live and simulated data is best made at rf level. Howeversimulations at video level or at plot level would allow for testing resolutioncapabilities from part(s) of the system, e.g. tracker-on-site or plot filter.

D.2.3 Live data from test transponders

Specific scenarios can be tested by making use of a fixed and a mobile testtransponder installed on a test site. Both transponders shall be programmablein range but the mobile transponder shall be able to step through the rangewindow with fixed discrete steps. The Mode C shall be encoded as to reflectthe separation in range with the precision of discrete range steps. Care shallbe taken with the selection of the site in order the (M)SSR replies to appear astypical.

D.2.4 Live data from traffic of opportunity

Resolution cases from live data shall be analysed to study the impact ofresolution as one of the factors playing a role in the degradation of the reliabilityand the quality of sensor data, e.g. statistics on the rate of occurrence etc. Byrecording and replaying data at one level one might be in a position to test theperformance of a system at a lower level in the processing chain, e.g.recordings at video level might allow for testing the monopulse postprocessing, recordings at plot level might allow for testing the plot filterfunctions or the local tracker for resolution. Use can be made of the fieldmonitor by programming its delay to coincide with a major airroute. This testshall be made when the radar is not operational.

D.2.5 Live data from test flights with (optional) support of DGPS data

The problem with resolution tests is the dependency on data which might bedegraded because of limitation of the resolution capabilities of the sensorsystem to be tested. Therefore a reference trajectory is required. GPS and in



particular differential GPS do provide a very good reference and is independentof the sensor itself. Precautions shall be taken to time tag the recorded sensordata with absolute time preferably derived from GPS unit.

D.3 Advantages and disadvantages of the different methods applied.

The advantages and disadvantages of the different methods applied are listedin the table below with regard to operational impact, capacity, duration of test,precision and the reference trajectory.

D.4 Detailed description of the different methods with presentation ofresults.

D.4.1 Test Flights

A scenario has been conceived whereby two test aircraft are used. Thescenario comprises two parts, one for testing range resolution and one fortesting azimuth resolution. The use of DGPS data for the reference positions isoptional. Both aircraft shall have properly installed and properly functioningtransponders.

D.4.1.1 Range resolution testing.

Two test aircraft are instructed to fly a radial trajectory. One aircraft keeps aconstant speed and heading. The other aircraft makes close approachesfollowing the other aircraft while keeping the same heading. The distance inrange between the two aircraft decreases gradually unto the moment whererange resolution does not exist anymore. The second aircraft increases againthe range separation until range resolution is reached again. This closeapproaching is repeated several times at different ranges of the radar. The testshall be performed in good visibility conditions under control of the ATCcontroller who stays in contact with the two pilots. The pilot of the secondaircraft may report his close approach distance (as measured by instrumentsavailable in the aircraft) to the ATC controller. The test shall be performed in asector which is cleared from traffic and at a flightlevel to guarantee goodcoverage. The parameters for PSR and SSR range resolution are different.Therefore both parameters have to be tested. In case of dual electronics, PSRdata only shall be connected to one plot filter channel with SSR data onlyconnected to the parallel plot filter channel. The ATC controller shall makeobservations on the data of both channels.

D.4.1.2 Azimuth resolution testing (see figure D.1.).

Two test aircraft are instructed to fly a radial trajectory. One aircraft flies with aconstant speed and a constant heading. The other aircraft flies in parallel withthe other aircraft within a fixed range separation and a constant offset S in NM,which however does change at regular range intervals. The offset S is selectedas to permit the assessment of azimuth resolution for a given azimuthseparation Dtheta, whereby measurement points become available before andafter lack of resolution.


Page D/4 Working Draft Edition 0.1 June 1997

D.4.2 Test transponders

A scenario has been conceived whereby two programmable test transpondersare used for the assessment of the resolution capabilities within the total closeproximity area for all the parameters to be tested.

D.5 Presentation of results

All results shall be presented in resolution diagram (Drho, Dtheta). There shallbe as many resolution diagrams as there are parameters to be tested, i.e.position detection, code detection, position accuracy in range, positionaccuracy in range, correct code detection and validation etc. The precision ofthe analysis depends on the method applied and the reference trajectory used.

AdvantagesandDisadvantages

Simulateddata

Combinationof live andsimulateddata

Live datafrom testtransponders

Live data fromtraffic ofopportunity

Live data from testflights with (optional)support of DGPS data

Operationalimpact

N/A. none if test isdone instandbychannel

small ifcareful

selection oftest rangewindow

none none

Capacity Huge asmeant to

test systemfor

maximumcapabilities

limited small limited asfunction of the

density oftraffic

only for test targetsavailable

Duration of test Function ofthe

precision ofthe

resolutiontest zone

as for normaltraffic

one step ofresolutiondiagram

tested perscan

eachresolution

case may lastseveral

minutes; verylong for a

representativesample

as long as test flightswill last

Precision limited bysimulator,e.g. 1/200

NM in rangeand 1 ACPin azimuthare typical

high if videorecording is

possible,otherwise

limited by LSBof plot and

trackmessages

medium asrange

separation isstored as FLinformationin plot/track

data

high if videorecording is

possible,otherwise

limited by LSBof plot and

trackmessages

high if videorecording is possible,otherwise limited byLSB of plot and track

messages

Referencetrajectory

controlledby simulator

partlycontrolled by

simulator

controlled bypositioning

of testtransponder

s

to be derivedfrom data but

could bederived from

recorded video

DGPS data will serveas reference data for

positioning withinresolution diagram



Figure D.1 Azimuth Resolution testing,

The azimuth resolution is measured at each interval. The second aircraft staysat a fixed offset which changes from interval to interval.