Aviation Weather Facilities at the Aviation Weather Facilities at the Hong Kong International AirportHong Kong International Airport

Olivia LeeOlivia Lee25 July 200525 July 2005

Airport Met. Observation System Airport Met. Observation System (AMOS)(AMOS)

Requirements/recommendations:Requirements/recommendations:ICAO Annex 3ICAO Annex 3ICAO references:ICAO references:Manual of Aeronautical Met. PracticeManual of Aeronautical Met. PracticeManual of Runway Visual Range Observing Manual of Runway Visual Range Observing and Reporting Practicesand Reporting PracticesWMO references:WMO references:WMO No. 6WMO No. 6WMO Technical Regulations No. 49WMO Technical Regulations No. 49

Built over the past few years to replace the AMOS processors and displays which operated since airport opening in 1998

Enhanced AMOSEnhanced AMOS

For processing of meteorological data collected from the sensors installed at and around the airport

Dual Link system – data transmitted from sensors via land lines and radio links to processors

AMOS processors (2 at at Airport Met. Office (AMO) and 2 at Backup AMO) will process data according to ICAO Amendment 73 to Annex 3 algorithms and present them on graphical displays for use by aviation forecasters, observers and air traffic controllers.

The data will also be automatically archived in database (one at AMO and one at Backup AMO) for compilation of climatological statistics.

Enhanced AMOS processors and displays was put into operation on 25 November 2004.

Enhanced AMOS (continued) Enhanced AMOS (continued)

Sensors included in enhanced AMOSSensors included in enhanced AMOSAnemometer R1W, R1C, R1E, R2W, R2C, R2E, NLS, Anemometer R1W, R1C, R1E, R2W, R2C, R2E, NLS, YTS, TMT, TO, SC, SHW and SLW, each with 2 YTS, TMT, TO, SC, SHW and SLW, each with 2 sensorssensors

TransmissometerTransmissometer and Forward and Forward ScattererScatterer at R1W, at R1W, R1C, R1E, R2W, R2C and R2E R1C, R1E, R2W, R2C and R2E

CeilographCeilograph at R1W, R1E, R2W and R2E, SMT and at R1W, R1E, R2W and R2E, SMT and Meteorological Garden (CLK)Meteorological Garden (CLK)

Thermometer and barometer at Meteorological Thermometer and barometer at Meteorological GardenGarden

Ogawa Ogawa raingaugeraingauge and and ObrometerObrometer

Weather Buoys and hilltop anemometers to be Weather Buoys and hilltop anemometers to be includedincluded

Runway AnemometersRunway Anemometers

Essential for Essential for airport airport operationoperationTakeTake--off and off and landing of landing of aircraftaircraftDual sensors Dual sensors for redundancyfor redundancy

Weather BuoyWeather Buoyan automatic weather station an automatic weather station mounted on a 3mounted on a 3--metre metre diameter buoydiameter buoymeasures wind, air pressure, measures wind, air pressure, temperature and humiditytemperature and humiditydata transmission by radio data transmission by radio link every 10 secondslink every 10 secondsoperating on solar power operating on solar power alonealoneuseful for detecting sea useful for detecting sea breeze or gust front breeze or gust front

ICAO Annex 3 requirements ICAO Annex 3 requirements (Section 4.5)(Section 4.5)

Sensors for surface wind observations Sensors for surface wind observations ……should be sited to give the best should be sited to give the best practicable indication of conditions along practicable indication of conditions along the runways, e.g. liftthe runways, e.g. lift--off and touchdown off and touchdown zones.zones.At aerodromes where topography or At aerodromes where topography or prevalent weather conditions cause prevalent weather conditions cause significant differences in surface wind at significant differences in surface wind at various sections of the runway, additional various sections of the runway, additional sensors should be provided.sensors should be provided.

1010--minute wind for METAR/SPECIminute wind for METAR/SPECI

22--minute wind for local routine and special reportsminute wind for local routine and special reports

Amendment 73 to ICAO Annex 3 to be implemented on 25 Amendment 73 to ICAO Annex 3 to be implemented on 25 Nov 2004 Nov 2004 –– Change of wind algorithmsChange of wind algorithms

Marked discontinuity (MD)Marked discontinuity (MD) in 10 minute wind :in 10 minute wind :(1) wind direction change >= 30 deg with a wind speed >= (1) wind direction change >= 30 deg with a wind speed >= 10 knots, 10 knots, oror(2) wind speed change >= 10 knots(2) wind speed change >= 10 knotsthat last at least 2 minutesthat last at least 2 minutes..The 10 minute wind average period, maximum 3The 10 minute wind average period, maximum 3--second second average gusts and extreme directions will be computed average gusts and extreme directions will be computed after the MD. after the MD.

Wind ReportingWind Reporting

Variable winds Variable winds should be reported in 10 minute and 2 should be reported in 10 minute and 2 minute wind directionminute wind direction

Definition: Definition: (a) the difference between 3(a) the difference between 3--second second average average extreme wind extreme wind directions is between 60 and 180 degrees and the wind directions is between 60 and 180 degrees and the wind speed is less than 3 knots; or speed is less than 3 knots; or

(b) (b) the difference between 3the difference between 3--second average extreme wind second average extreme wind directions is 180 degrees or more.directions is 180 degrees or more.

Wind can change very fast Wind can change very fast ……

Change of synoptic condition, e.g. arrival of Change of synoptic condition, e.g. arrival of cold front)cold front)

Gusty winds, e.g. tropical cyclonesGusty winds, e.g. tropical cyclones

Severe weather, e.g. squalls, gust fronts of Severe weather, e.g. squalls, gust fronts of thunderstormsthunderstorms

Fine and relatively calm days Fine and relatively calm days ……sea breeze!sea breeze!

MD and Variable winds occur in onset and retreat of MD and Variable winds occur in onset and retreat of sea breezesea breeze

10 minute wind variations

2 minute mean wind direction in degrees /wind speed in knots, reading turns red when wind speed exceeds 22 kts

3 second average gust in last 2 minutes in kts

2 minute mean cross wind at 25R in kts, reading turns red when exceeding 25 kts

AMOS Graphical Display showing wind products

2 minute mean head wind at 25R in kts, reading turns red when exceeding 15 kts

10 second mean wind direction in degrees /wind speed in kts

Observer program for issuance of SYNOP/METAR/SPECI

1 minute and 10 minute mean Forward Scatterer (F/S) visibility (i.e. the larger value between 1 minute F/S MOR and night-time visibility calculated based on 1000 cd). If the F/S visibility is night-time visibility, the reading here will turn black over yellow background.

Box showing 1 minute mean mean sea level pressure, QFE, QNH and Station Level Pressure

3 second average maximum and minimum gust in last 10 minutes

Click to display latest 00th or 30th minute data 3 second average left and right extreme wind direction in last 10 minutes

Click to display latest minute’s data

3 second average maximum gust in last hour

Box showing rainfall data

Get 2 min wd program for issuance of Local Routine Report

3 second average left and right extreme wind direction in last 10 minutes

2 minute mean wind direction in degrees and wind speed

3 second average maximum and minimum gust in last 10 minutes

All runway wind data of the time specified will be listed out in this box, moving slide bar to see

Visibility and Runway Visual Range Visibility and Runway Visual Range (ICAO Annex 3)(ICAO Annex 3)

VisibilityVisibility for aeronautical purpose is the greater of:for aeronautical purpose is the greater of:

(a) the greatest distance at which a black object of (a) the greatest distance at which a black object of suitable dimensions, situated near the ground, can be suitable dimensions, situated near the ground, can be seen and recognized when observed against a bright seen and recognized when observed against a bright background (the background (the ““daytime visibilitydaytime visibility””))

(b) the greatest distance at which lights in the vicinity (b) the greatest distance at which lights in the vicinity of 1000 candelas can be seen and identified against of 1000 candelas can be seen and identified against an unlit background (the an unlit background (the ““nighttimenighttime”” visibility)visibility)

(a) is also called meteorological optical range ((a) is also called meteorological optical range (MORMOR))

(b) varies with background illumination(b) varies with background illumination

Runway Visual Range (RVR)Runway Visual Range (RVR)

The range over which the pilot of an aircraft on the The range over which the pilot of an aircraft on the centre line of a runway can see the runway surface centre line of a runway can see the runway surface markings or the lights delineating the runway or markings or the lights delineating the runway or identifying its centre line.identifying its centre line.

It depends on:It depends on:

-- MORMOR-- Runway light intensities (edge lights, centre lights)Runway light intensities (edge lights, centre lights)-- Background luminanceBackground luminance

FormulaFormulaLn(epsilonLn(epsilon) * RVR) * RVR

MOR = MOR = ------------------------------------------------------------------------------Ln(EtLn(Et) + 2*) + 2*Ln(RVRLn(RVR) ) –– Ln(ILn(I))

wherewhereepsilon = visual threshold of luminance epsilon = visual threshold of luminance

contrast (0.05)contrast (0.05)Et = illumination threshold (a function of Et = illumination threshold (a function of

background luminance)background luminance)I = runway light intensity (usually a number I = runway light intensity (usually a number

of steps)of steps)

TransmissometerTransmissometer (3 on each runway) (3 on each runway)

The transmitter radiates short high-powered light pulses at a frequency of approx. 180 flashes/minute.

The receiver responds only to these light pulses and measures their intensity.

TransmissometerTransmissometerAdvantagesAdvantages-- larger measurement volume larger measurement volume --> more > more representativerepresentative-- direct measurement of light intensity change direct measurement of light intensity change due to suspending particulates and water due to suspending particulates and water dropletsdropletsProblemsProblems-- lenses easily contaminatedlenses easily contaminated-- birds resting on sensor headsbirds resting on sensor heads-- limitation of measurement range (up to 2 km) limitation of measurement range (up to 2 km) -- frequent optical alignment requiredfrequent optical alignment required

Forward Forward scattererscatterer (look(look--down type, 3 on down type, 3 on each runway)each runway)

Evaluates MOR by measuring the intensity of infrared light scattered at an angle of 33 degrees

Forward Forward scattererscatterer

AdvantagesAdvantages-- looklook--down type: better prevention of down type: better prevention of lens contaminationlens contamination-- larger measurement range (at least 10 larger measurement range (at least 10 km, maybe up to 50 km!)km, maybe up to 50 km!)ProblemsProblems-- smaller measurement volumesmaller measurement volume-- scattering angles varies with the type of scattering angles varies with the type of suspending particulate and precipitationsuspending particulate and precipitation

How good (or consistent) are the visibility data How good (or consistent) are the visibility data from different sensors?from different sensors?

Annex 3 recommendationsAnnex 3 recommendations (Sections 4.6 and 4.7)(Sections 4.6 and 4.7)

Manual insertion of visibility dataManual insertion of visibility dataRepresentative of takeRepresentative of take--off and landing off and landing areasareasCalibration of a forwardCalibration of a forward--scattererscatterer meter meter has to be traceable and verifiable to a has to be traceable and verifiable to a transmissometertransmissometer standardstandardRVR RVR –– special treatment for light intensity special treatment for light intensity of 3 percent or lessof 3 percent or lessRVR RVR –– beware of marked discontinuitybeware of marked discontinuityRVR RVR –– trend (U, D and N)trend (U, D and N)

RVR trend definition:

Divide the averaging period of 10 minutes into two half, each of 5 minutes:

Trend

U: if RVR(2nd half) – RVR(1st half) >=100 m

D: if RVR(1st half) – RVR (2nd half) >=100 m

N: if both of the above values < 100 m

1 minute mean Forward Scatterer (F/S) visibility (the larger value between 1 minute F/S MOR and night-time visibility calculated based on 1000 cd.

1 minute mean RVR (trend symbols)

Tendency definition: Divide the averaging period of 10 minutes into two half, each of 5 minutes: Tendency ‘U’ – if RVR(2nd half) – RVR(1st half) >=100 mTendency ‘D’ – if RVR(1st half) – RVR (2nd half) >=100 mTendency ‘N’ – if both of the above values < 100 m

AMOS Graphical Display showing visibility products

Cloud Cloud –– ICAO Annex 3, Section 4.9ICAO Annex 3, Section 4.9

Cloud amount, type and base heightCloud amount, type and base heightRepresentative of middle marker site Representative of middle marker site (1 nm) of the instrument landing (1 nm) of the instrument landing systemsystemReference: aerodrome elevationReference: aerodrome elevation

Cloud base heightCloud base heightLaser Laser ceilometerceilometer

Problems with laser Problems with laser ceilometerceilometer

Point measurement, e.g. cloud break Point measurement, e.g. cloud break overhead of overhead of ceilometerceilometer, slanting , slanting cumulus towercumulus towerRange of detection decreases rapidly Range of detection decreases rapidly in rain in rain --> no cloud base!> no cloud base!Effect of direct sunlight Effect of direct sunlight –– solar solar shuttershutter

Cloud amount Cloud amount –– automation?automation?

AMOS Graphical Display showing cloud base

((NNo o CClouds louds DDetected)etected)

““Conventional instrumentsConventional instruments”” at at Meteorological GardenMeteorological Garden

Dry and wet bulb Dry and wet bulb thermometers thermometers –– aspiratedaspirated

DropDrop--counting, tipping counting, tipping bucket bucket raingaugesraingauges and and obrometersobrometers are used for are used for measuring rainfall.measuring rainfall.

Barometers Barometers –– three units three units working in parallel:working in parallel:e.g. when 2 or more e.g. when 2 or more values are equal values are equal --> > choose this value, choose this value, otherwise use the middle otherwise use the middle valuevalue

AMOS Graphical Display of pressure, temperature and rainfall data

Wind Profiler Wind Profiler (Vertically Pointing Radar) (Vertically Pointing Radar)

Wind profiler basicsWind profiler basicsRADAR (RADAR (RARAdiodio DDetection etection AAnd nd RRanging) anging) •• Conventional Weather Radar detects reflections from Conventional Weather Radar detects reflections from

objects in the air (e.g. hydrometeors)objects in the air (e.g. hydrometeors)•• Scanning horizontally and Scanning horizontally and ““slicingslicing”” vertically a few vertically a few

degreesdegreesWind Profiler RADARWind Profiler RADAR•• Measuring from ground and vertically UP, Clear Air Measuring from ground and vertically UP, Clear Air

RADARRADAR•• Reflection detected from turbulence and eddiesReflection detected from turbulence and eddies•• Wind Profilers operate below weather radar frequenciesWind Profilers operate below weather radar frequencies•• Typical frequencies used in wind profilingTypical frequencies used in wind profiling

4545--65 MHz65 MHz404404--482 MHz482 MHz915915--924 MHz924 MHz12801280--1357.5 MHz1357.5 MHz

Wind profilerWind profiler

Antenna

Transmitter Receiver

Controller

SignalProcessor

Computer

Functional blocks in WP system

Basics.. Remote SensingBasics.. Remote SensingRemote Sensing from the Ground Vertically UPRemote Sensing from the Ground Vertically UP•• Either Acoustic or electromagnetic pulse or both is sent Either Acoustic or electromagnetic pulse or both is sent

into the atmosphereinto the atmosphere•• Detection of the signal backscattered from refractive Detection of the signal backscattered from refractive

index index inhomogenetiesinhomogeneties in the atmospherein the atmosphere•• In clear air the scattering targets are the temperature In clear air the scattering targets are the temperature

and humidity fluctuations produced by turbulent eddiesand humidity fluctuations produced by turbulent eddies•• Scale is about half of the wavelength for the transmitted Scale is about half of the wavelength for the transmitted

radiationradiation•• The wavelengths of the acoustic (SODAR) and The wavelengths of the acoustic (SODAR) and

electromagnetic (WIND PROFILER) instruments are 0.07 electromagnetic (WIND PROFILER) instruments are 0.07 to 0.18m or 0.24m to 0.18m or 0.24m ----> thus sensitive to similar parts of > thus sensitive to similar parts of the turbulent spectrum the turbulent spectrum

Wind Profiler RADAR BackscatterWind Profiler RADAR Backscatter

Types of Radar scatteringTypes of Radar scatteringScattering from atmospheric targets:Scattering from atmospheric targets:•• irregularities in the index of refraction of the airirregularities in the index of refraction of the air•• hydrometeors, particularly wet ones (rain, melting snow, hydrometeors, particularly wet ones (rain, melting snow,

water coated ice)water coated ice)•• birds and insects (frequency dependant)birds and insects (frequency dependant)•• smoke plumessmoke plumes

Multitude of targets may introduce serious errorsMultitude of targets may introduce serious errors•• the measured velocity is that of rain, not windthe measured velocity is that of rain, not wind

Interfering signals:Interfering signals:•• ground and sea clutterground and sea clutter•• aircraft and migrating birdsaircraft and migrating birds•• RFI (depends on frequency band)RFI (depends on frequency band)

Doppler Beam Swinging (DBS)Doppler Beam Swinging (DBS)•• DBS method for wind DBS method for wind

vector calculations (u,v,w)vector calculations (u,v,w)•• radial scattered velocities radial scattered velocities

measured with one vertical measured with one vertical and 2 (4) offand 2 (4) off--zenith beamszenith beams

•• beambeam--pointing sequence is pointing sequence is repeated every 1repeated every 1--5 5 minutesminutes

•• Electronic beam pointing Electronic beam pointing with phase shifters using with phase shifters using one antennaone antenna

•• local horizontal uniformity local horizontal uniformity of the wind field is of the wind field is assumedassumed

Doppler shiftDoppler shift•• Doppler Doppler FormulaFormula::

•• Measurement of wind speed based on the Doppler shift Measurement of wind speed based on the Doppler shift in the received signal:in the received signal:

where where VrVr is the radial velocity of the is the radial velocity of the scatterersscatterers

•• Examples of Wind Profiler Doppler shift (radial velocity Examples of Wind Profiler Doppler shift (radial velocity 10m/s)10m/s)

50MHz, wavelength 6m, Doppler shift 3.34Hz50MHz, wavelength 6m, Doppler shift 3.34Hz449MHz, wavelength 0.66815m, Doppler shift 449MHz, wavelength 0.66815m, Doppler shift 29.9Hz29.9Hz1290MHz, wavelength 0.23m, Doppler shift 86Hz1290MHz, wavelength 0.23m, Doppler shift 86Hz

λr

DVf 2−=

Signal Processing StepsSignal Processing Steps

Consensus Algorithm ProcedureConsensus Algorithm Procedure

0 +Nyquist-Nyquist 0 +Nyquist-Nyquist 0 +Nyquist-Nyquist

0 +Nyquist-Nyquist 0 +Nyquist-Nyquist 0 +Nyquist-Nyquist

0 +Nyquist-Nyquist 0 +Nyquist-Nyquist 0 +Nyquist-Nyquist

0 +Nyquist-Nyquist 0 +Nyquist-Nyquist 0 +Nyquist-Nyquist

0 +Nyquist-Nyquist 0 +Nyquist-Nyquist 0 +Nyquist-Nyquist

0 +Nyquist-Nyquist 0 +Nyquist-Nyquist 0 +Nyquist-Nyquist

0 +Nyquist-Nyquist 0 +Nyquist-Nyquist 0 +Nyquist-Nyquist

0 +Nyquist-Nyquist 0 +Nyquist-Nyquist 0 +Nyquist-Nyquist

Oblique1 radial velocity Oblique2 radial velocity (orthogonal to 1)

Vertical radial velocity

Moments collected over the interval of the consensus averaging period

Consensus radial velocity calculation

One range gate

Oblique consensus window width, m/s

Oblique consensus window width, m/s

Vertical consensus window width, m/s

To be valid, the number of radial velocity samples within the window must exceed the consensus percentage. If valid, the mean of the velocities within the window is the radial velocity of the consensus period.

If the all radial velocities are valid, then a wind speed and direction is calculated for the consensus period.

RASSRASSRadio Acoustic Sounding System (RASS)Radio Acoustic Sounding System (RASS)•• Provides profiles of virtual temperatureProvides profiles of virtual temperature•• Emits a strong Emits a strong continuoscontinuos (5 minutes/hour) acoustic sine (5 minutes/hour) acoustic sine

wave synchronized to RADAR frequencywave synchronized to RADAR frequencyFe 1290MHzFe 1290MHz-------->RASS output 2580Hz (half >RASS output 2580Hz (half wavelength)wavelength)

•• Tone burst travels as a compression wave with the Tone burst travels as a compression wave with the speed of sound upwards in the atmospherespeed of sound upwards in the atmosphere

•• Wind Profiler measures the speed of propagation of the Wind Profiler measures the speed of propagation of the sound burstsound burst

•• Since the speed of sound depends on the air Since the speed of sound depends on the air temperature, virtual temperature can be computed from temperature, virtual temperature can be computed from the received signalthe received signal

Wind profilers in Hong KongWind profilers in Hong Kong

AirportSiu Ho Wan

Sha Lo Wan

Sham Shui Po

Cheung Chau

Operating modesOperating modes1299 MHz boundary layer profilers1299 MHz boundary layer profilersLow mode:Low mode:120 120 –– 1500 m, 60 m range, 10 min.1500 m, 60 m range, 10 min.High mode:High mode:210 210 –– 6000 m, 200 m range, 10 min.6000 m, 200 m range, 10 min.““Very highVery high”” mode:mode:210 210 –– 9000 m, 200 m range, 10 min.9000 m, 200 m range, 10 min.Data: horizontal wind, vertical velocity, Data: horizontal wind, vertical velocity, signal noise ratio, spectral widthsignal noise ratio, spectral width

ApplicationsApplicationsHeavy rainHeavy rain

W

7H

NW

13H

E

Vertical velocityVertical velocity

R

-10

-3

+2

W

Jet stream Jet stream –– related to heavy rainrelated to heavy rain

22H

J

J

14H

Low level jet streamLow level jet stream

Tropical cycloneTropical cyclone

YXHK

Wind fieldWind field

25 m/s25

15

10

510

15

0H15H 15H8/9/96 9/9/96

C

Reception of World Area Forecast System Reception of World Area Forecast System (WAFS) products (WAFS) products

In the ICAO framework, WAFS provides meteorological authorities and authorized users with aeronautical meteorological information

OPMET – in alphanumeric format

Upper-air wind and temperature data – in GRIB format

Weather charts – in T4 facsimile format as well as BUFR format

2 World Area Forecast Centres (WAFC) – London and Washington

broadcast the WAFS products via satellites.

VSAT equipment installed at the airport and the Observatory Headquarters for reception of the WAFC broadcast

A Prognostic Significant Weather Chart generated from BURF data broadcast by London WAFC

Thank You

Weather Buoys

Runway Anemometers

Other anemometers surrounding the airport

System Block Diagram for AMOS Processors and Graphical Displays