Getting a Bearing on ASF Directional Corrections 32 nd Annual Technical Symposium International Loran Association 5 Nov 2003 Boulder, CO

Getting a Bearing on ASF Getting a Bearing on ASF Directional CorrectionsDirectional Corrections

3232ndnd Annual Technical Symposium Annual Technical Symposium International Loran AssociationInternational Loran Association

5 Nov 20035 Nov 2003

Boulder, COBoulder, CO

11/5/0311/5/03 USCGA-JJMA Presentation for ILA 32USCGA-JJMA Presentation for ILA 32 22

AuthorsAuthors CAPT Richard HartnettCAPT Richard Hartnett

US Coast Guard AcademyUS Coast Guard Academy

Gregory JohnsonGregory Johnson John J. McMullen Assoc. Inc.John J. McMullen Assoc. Inc.

Dr. Peter SwaszekDr. Peter Swaszek University of Rhode IslandUniversity of Rhode Island

Ken DykstraKen Dykstra John J. McMullen Assoc. Inc.John J. McMullen Assoc. Inc.


OutlineOutline

IntroductionIntroduction Problem identificationProblem identification Error Sources and SolutionsError Sources and Solutions SummarySummary


IntroductionIntroduction

LORAN-C as “the” backup for GPSLORAN-C as “the” backup for GPS Accuracy, availability, integrity, continuity Accuracy, availability, integrity, continuity

Accuracy:Accuracy: Needs:Needs:

Aviation: NPA – RNP 0.3 (309 meters) Maritime: HEA (8-20 meters)

Limitations: Limitations: Spatial and temporal variations in TOA (ASF)

observed by the receiver and presented to the position solution algorithm


Loran 2003+Loran 2003+

Multi-station, multi-chain, all-in-view Multi-station, multi-chain, all-in-view receiverreceiver

TOA vs. TD measurementsTOA vs. TD measurements Separate “errors” into spatial, temporal, Separate “errors” into spatial, temporal,

and directional componentsand directional components DSP-based receiversDSP-based receivers H-field vs. E-field antennasH-field vs. E-field antennas Grid approach vs. waypointsGrid approach vs. waypoints


Current ResearchCurrent Research

USCGA/JJMA activities: USCGA/JJMA activities: Explore ways to mitigate TOA variationExplore ways to mitigate TOA variation Current approach:Current approach:

Model the ASF sources Spatial effectsSpatial effects Temporal effectsTemporal effects

Model the directional effects (H-field) Estimate parameters/values for the models “Correct” the TOA observations using the models

Of interest today


ASF Variation ModelASF Variation Model

Assume that the variation in the observed TOAs Assume that the variation in the observed TOAs can be decomposed into 3 independent, additive can be decomposed into 3 independent, additive terms:terms: Spatial term:Spatial term:

Due to differences in the Loran signal propagation path

Temporal term:Temporal term: For short term TOA variability on a local region

Directional term:Directional term: Based on the relative bearing of the Loran tower to

the vessel

Key assumptions


Block diagram of approachBlock diagram of approach

TOAs From Rcvr

TOAs To Position Algorithm

ASF Temporal Correction

ASF Spatial Correction

Antenna Direction Correction

Live MonitorUpdate

Recent Position

Current Heading


Problem identificationProblem identification First noticed directional TOA in our data sets over a year First noticed directional TOA in our data sets over a year

ago, started investigating:ago, started investigating: Have numerous examples of this:Have numerous examples of this:

Airplane rotation data on groundAirplane rotation data on ground Convair 580 Ohio University King Air Locus antenna/Satmate rcvr Megapulse antenna/DDC rcvr

Airplane rotation data in airAirplane rotation data in air Convair in CA both rcvrs/antennas Rockwell data – Locus antenna/satmate

Boat rotationsBoat rotations T-boats Both Megapulse antenna/DDC and Locus antenna/satmate

Field data, various antennasField data, various antennas DDC, aircraft antenna, small antennas, split loop antennas


Graphs of TOA variationGraphs of TOA variation

10 15 20 25 30 35 40 45 50 55-2

-1

0

1

2

3

4

5

6Antenna rotation 11 Sept 02; ASF Corrections for 9960

Mic

rose

cond

s

Time (minutes) Seneca - black Caribou - blue Nantucket - green Carolina-B - read Dana - cyan

0 50 100 150 200 250 300 350-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4SatMate Loop Coupling

TO

A, d

iffe

ren

ce

fro

m m

edia

n,

sec

Heading

9960-Seneca9960-Caribou9960-Nantucket9960-Carolina Beach

Field – DDC – Split Loops

Field – SatMate - Locus

0 50 100 150 200 250 300 3500.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Heading

AS

F,

se

c

9960

SenecaCaribouNantucketCarolina-B

Tboat – DDC - Megapulse

Convair – PC104 - Megapulse

0 50 100 150 200 250 300 350-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

Heading

TO

A c

ha

ng

e,

se

c

Relative TOA Variations 9960 Chain - Split Loops on Lower Field

9960-Seneca9960-Caribou9960-Nantucket9960-Carolina-B


Expected Position ErrorExpected Position Error

Given that there are TOA variations as the Given that there are TOA variations as the antenna is rotated, what is the effect in the antenna is rotated, what is the effect in the position domain?position domain?


Model of TOA VariationsModel of TOA Variations

0 50 100 150 200 250 300 350-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

Bearing

TO

A o

ffs

et

Model of antenna delay

SenecaCaribouNantucketCarolina Beach


Resulting Position ErrorResulting Position Error

0 50 100 150 200 250 300 3500

10

20

30

40

50

60

70

Bearing

Po

sit

ion

err

or

in m

ete

rs

95% error bound

Position Error as Antenna is Rotating

noise onlycoupling onlyboth


Position Error relative to centerPosition Error relative to center

-60 -40 -20 0 20 40 60-40

-30

-20

-10

0

10

20

30

40

Error in meters

Err

or

in m

ete

rsPosition Error as Antenna is Rotated

noise onlycoupling onlyboth


Error SourcesError Sources

Time delayTime delay CouplingCoupling Antenna phase issuesAntenna phase issues Reradiation\Local EffectsReradiation\Local Effects


Time DelayTime Delay

Unequal phase delay between the two Unequal phase delay between the two channels leads to directional TOA channels leads to directional TOA variationvariation

SourcesSources Amplifier/FiltersAmplifier/Filters CablesCables AntennasAntennas


Time Delay – Theoretical Time Delay – Theoretical FormulationFormulation

tteA

tteA

sin90cos:2 Channel

sincos:1 Channel

tteA

tteA

sin90cos:2 Channel

sincos:1 Channel

Ideal

Actual

offset phase channel-inter

envelope signal

arrival signal ofdirection

amplitude signal

te

A


Theoretical Effect of Time Theoretical Effect of Time DifferenceDifference

0 50 100 150 200 250 300 350 400-80

-60

-40

-20

0

20

40

60

80

Angle of Rotation, degrees

TO

A V

ari

ati

on

, ns

ec

TOA error as a function of phase difference (degrees)

012345


Measured Time DelayMeasured Time DelayLoran Simulator

(ICS660 card)RF Front End

(Freq Devices gain modules and filters)

Ch 1

Ch 2

RF in RF out

Loran Receiver(ICS 650 card)

Ch 1

Ch 2



S/w compensation for time delayS/w compensation for time delay


CouplingCoupling

Some coupling seen with combined loops Some coupling seen with combined loops vs. with split loopsvs. with split loops Maximize strong signal on one loopMaximize strong signal on one loop Should be zero on other loopShould be zero on other loop

This is not the case with some H-field This is not the case with some H-field antennasantennas Maximize strong signal on one loopMaximize strong signal on one loop Signal is NOT zero on other loopSignal is NOT zero on other loop



Single Loop Phase IssueSingle Loop Phase IssueLoop Antenna Phase

-210

-180

-150

-120

-90

-60

-30

0

30

60

90

120

150

180

210

0 30 60 90 120 150 180 210 240 270 300 330 360

angle of rotation

Ph

as

e (d

eg

ree

s)

Ideal

Actual


Strongest Beam OnlyStrongest Beam Only

0 200 400 600 800 1000 1200 1400 1600 1800 2000

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

Time (seconds)

Rel

ativ

e TO

A (

usec

)TOAs with Stongest Loop

Seneca Nantucket


Strongest Beam and Delay Strongest Beam and Delay CorrectionCorrection

0 200 400 600 800 1000 1200 1400 1600 1800 2000

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

Time (seconds)

Rel

ativ

e TO

A (

usec

)TOAs with Stongest Loop and 5 degrees phase shift

Seneca Nantucket


SummarySummary

Split loops (coupling)Split loops (coupling) Works – when strong signal is max. in one Works – when strong signal is max. in one

loop is zero on other looploop is zero on other loop

Time delay correction in softwareTime delay correction in software Works - compensate for unequal delay in Works - compensate for unequal delay in

antenna and/or amplifierantenna and/or amplifier

Loop Phase Shift effectLoop Phase Shift effect Use antenna loop with largest magnitude onlyUse antenna loop with largest magnitude only


Final RemarksFinal Remarks When faced with tremendous coupled When faced with tremendous coupled

challenges we find the best strategy is to challenges we find the best strategy is to do what most engineers on the team do – do what most engineers on the team do – blame Mitch!blame Mitch!

In the future, for harbor mapping we will In the future, for harbor mapping we will use both E and H-field antennas – use both E and H-field antennas – mappings may not be the same -mappings may not be the same -

We are highlighting “solvable challenges” We are highlighting “solvable challenges” with H-field antennaswith H-field antennas New Locus antennasNew Locus antennas New Reelelektronica antennasNew Reelelektronica antennas

Presentation by Wouter tomorrow

Calibration is clearly an important issue – Calibration is clearly an important issue – Must be done in lab and after installation! Must be done in lab and after installation!


AcknowledgementsAcknowledgements

Mitch Narins, FAA ANDMitch Narins, FAA AND JJMA TeamJJMA Team

Christian OatesChristian Oates George SandersGeorge Sanders Ruslan ShalaevRuslan Shalaev Tim WaldieTim Waldie

[email protected]@exmail.uscga.edu

[email protected]@jjma.com

[email protected]@ele.uri.edu

Documents

Getting a Bearing on ASF Directional Corrections 32 nd Annual Technical Symposium International Loran Association 5 Nov 2003 Boulder, CO