Aviation Weather Facilities at the Hong Kong International Airport. Olivia Lee 25 July 2005

Transcription

1 Aviation Weather Facilities at the Hong Kong International Airport Olivia Lee 25 July 2005

2 Airport Met. Observation System (AMOS) Requirements/recommendations: ICAO Annex 3 ICAO references: Manual of Aeronautical Met. Practice Manual of Runway Visual Range Observing and Reporting Practices WMO references: WMO No. 6 WMO Technical Regulations No. 49

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

4 Enhanced AMOS (continued) 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.

5 Sensors included in enhanced AMOS Anemometer R1W, R1C, R1E, R2W, R2C, R2E, NLS, YTS, TMT, TO, SC, SHW and SLW, each with 2 sensors Transmissometer and Forward Scatterer at R1W, R1C, R1E, R2W, R2C and R2E Ceilograph at R1W, R1E, R2W and R2E, SMT and Meteorological Garden (CLK) Thermometer and barometer at Meteorological Garden Ogawa raingauge and Obrometer Weather Buoys and hilltop anemometers to be included

6 Runway Anemometers Essential for airport operation Take-off and landing of aircraft Dual sensors for redundancy

7 Weather Buoy an automatic weather station mounted on a 3-metre 3 diameter buoy measures wind, air pressure, temperature and humidity data transmission by radio link every 10 seconds operating on solar power alone useful for detecting sea breeze or gust front

8 ICAO Annex 3 requirements (Section 4.5) Sensors for surface wind observations should be sited to give the best practicable indication of conditions along the runways, e.g. lift-off and touchdown zones. At aerodromes where topography or prevalent weather conditions cause significant differences in surface wind at various sections of the runway, additional sensors should be provided.

9 Wind Reporting 10-minute wind for METAR/SPECI 2-minute wind for local routine and special reports Amendment 73 to ICAO Annex 3 to be implemented on 25 Nov 2004 Change of wind algorithms Marked discontinuity (MD) in 10 minute wind : (1) wind direction change >= 30 deg with a wind speed >= 10 knots, or (2) wind speed change >= 10 knots that last at least 2 minutes. The 10 minute wind average period, maximum 3-second 3 average gusts and extreme directions will be computed after the MD.

10 Variable winds should be reported in 10 minute and 2 minute wind direction Definition: (a) the difference between 3-second 3 average extreme wind directions is between 60 and 180 degrees and the wind speed is less than 3 knots; or (b) the difference between 3-second 3 average extreme wind directions is 180 degrees or more.

11 Wind can change very fast Change of synoptic condition, e.g. arrival of cold front) Gusty winds, e.g. tropical cyclones Severe weather, e.g. squalls, gust fronts of thunderstorms Fine and relatively calm days sea breeze!

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

13 AMOS Graphical Display showing wind products 10 minute wind variations 10 second mean wind direction in degrees /wind speed in kts 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 head wind at 25R in kts, reading turns red when exceeding 15 kts 2 minute mean cross wind at 25R in kts, reading turns red when exceeding 25 kts

14 Observer program for issuance of SYNOP/METAR/SPECI Click to display latest 00 th or 30 th minute data 3 second average left and right extreme wind direction in last 10 minutes 3 second average maximum and minimum gust in last 10 minutes Click to display latest minute s data 3 second average maximum gust in last hour 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 Box showing rainfall data

15 Get 2 min wd program for issuance of Local Routine Report 2 minute mean wind direction in degrees and wind speed 3 second average maximum and minimum gust in last 10 minutes 3 second average left and right extreme wind direction in last 10 minutes All runway wind data of the time specified will be listed out in this box, moving slide bar to see

16 Visibility and Runway Visual Range (ICAO Annex 3) Visibility for aeronautical purpose is the greater of: (a) the greatest distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognized when observed against a bright background (the daytime visibility ) (b) the greatest distance at which lights in the vicinity of 1000 candelas can be seen and identified against an unlit background (the nighttime visibility) (a) is also called meteorological optical range (MOR( MOR) (b) varies with background illumination

17 Runway Visual Range (RVR) The range over which the pilot of an aircraft on the centre line of a runway can see the runway surface markings or the lights delineating the runway or identifying its centre line. It depends on: - MOR - Runway light intensities (edge lights, centre lights) - Background luminance

18 Formula Ln(epsilon) ) * RVR MOR = Ln(Et) ) + 2*Ln(RVR Ln(RVR) Ln(I) where epsilon = visual threshold of luminance contrast (0.05) Et = illumination threshold (a function of background luminance) I = runway light intensity (usually a number of steps)

19 Transmissometer (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.

20 Transmissometer Advantages - larger measurement volume -> > more representative - direct measurement of light intensity change due to suspending particulates and water droplets Problems - lenses easily contaminated - birds resting on sensor heads - limitation of measurement range (up to 2 km) - frequent optical alignment required

21 Forward scatterer (look-down type, 3 on each runway) Evaluates MOR by measuring the intensity of infrared light scattered at an angle of 33 degrees

22 Forward scatterer Advantages - look-down type: better prevention of lens contamination - larger measurement range (at least 10 km, maybe up to 50 km!) Problems - smaller measurement volume - scattering angles varies with the type of suspending particulate and precipitation

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

24 Annex 3 recommendations (Sections 4.6 and 4.7) Manual insertion of visibility data Representative of take-off and landing areas Calibration of a forward-scatterer meter has to be traceable and verifiable to a transmissometer standard RVR special treatment for light intensity of 3 percent or less RVR beware of marked discontinuity RVR trend (U, D and N)

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

26 AMOS Graphical Display showing visibility products 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(2 nd half) RVR(1 st half) >=100 m Tendency D if RVR(1 st half) RVR (2 nd half) >=100 m Tendency 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.

27 Cloud ICAO Annex 3, Section 4.9 Cloud amount, type and base height Representative of middle marker site (1 nm) of the instrument landing system Reference: aerodrome elevation

28 Cloud base height Laser ceilometer

29 Problems with laser ceilometer Point measurement, e.g. cloud break overhead of ceilometer,, slanting cumulus tower Range of detection decreases rapidly in rain -> > no cloud base! Effect of direct sunlight solar shutter

30 Cloud amount automation?

31 AMOS Graphical Display showing cloud base (No Clouds Detected)

32 Conventional instruments at Meteorological Garden Dry and wet bulb thermometers aspirated Drop-counting, tipping bucket raingauges and obrometers are used for measuring rainfall. Barometers three units working in parallel: e.g. when 2 or more values are equal -> choose this value, otherwise use the middle value

33 AMOS Graphical Display of pressure, temperature and rainfall data

34 Wind Profiler (Vertically Pointing Radar)

35 Wind profiler basics RADAR (RA( RAdio Detection And Ranging) Conventional Weather Radar detects reflections from objects in the air (e.g. hydrometeors) Scanning horizontally and slicing vertically a few degrees Wind Profiler RADAR Measuring from ground and vertically UP, Clear Air RADAR Reflection detected from turbulence and eddies Wind Profilers operate below weather radar frequencies Typical frequencies used in wind profiling MHz MHz MHz MHz

36 Wind profiler Functional blocks in WP system Antenna Transmitter Receiver Signal Processor Controller Computer

37 Basics.. Remote Sensing Remote Sensing from the Ground Vertically UP Either Acoustic or electromagnetic pulse or both is sent into the atmosphere Detection of the signal backscattered from refractive index inhomogeneties in the atmosphere In clear air the scattering targets are the temperature and humidity fluctuations produced by turbulent eddies Scale is about half of the wavelength for the transmitted radiation The wavelengths of the acoustic (SODAR) and electromagnetic (WIND PROFILER) instruments are 0.07 to 0.18m or 0.24m --> > thus sensitive to similar parts of the turbulent spectrum

38 Wind Profiler RADAR Backscatter

39 Types of Radar scattering Scattering from atmospheric targets: irregularities in the index of refraction of the air hydrometeors, particularly wet ones (rain, melting snow, water coated ice) birds and insects (frequency dependant) smoke plumes Multitude of targets may introduce serious errors the measured velocity is that of rain, not wind Interfering signals: ground and sea clutter aircraft and migrating birds RFI (depends on frequency band)

40 Doppler Beam Swinging (DBS) DBS method for wind vector calculations (u,v,w) radial scattered velocities measured with one vertical and 2 (4) off-zenith beams beam-pointing sequence is repeated every 1-51 minutes Electronic beam pointing with phase shifters using one antenna local horizontal uniformity of the wind field is assumed

41 Doppler Formula: Doppler shift f D 2V = Measurement of wind speed based on the Doppler shift in the received signal: where Vr is the radial velocity of the scatterers Examples of Wind Profiler Doppler shift (radial velocity 10m/s) 50MHz, wavelength 6m, Doppler shift 3.34Hz 449MHz, wavelength m, Doppler shift 29.9Hz 1290MHz, wavelength 0.23m, Doppler shift 86Hz r λ

42 Signal Processing Steps

43 Consensus Algorithm Procedure One range gate Oblique1 radial velocity Oblique2 radial velocity (orthogonal to 1) Vertical radial velocity -Nyquist 0 +Nyquist -Nyquist 0 +Nyquist -Nyquist 0 +Nyquist -Nyquist 0 +Nyquist -Nyquist 0 +Nyquist -Nyquist 0 +Nyquist Moments collected over the interval of the consensus averaging period -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 Consensus radial velocity calculation 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.

44 RASS Radio Acoustic Sounding System (RASS) Provides profiles of virtual temperature Emits a strong continuos (5 minutes/hour) acoustic sine wave synchronized to RADAR frequency Fe 1290MHz >RASS output 2580Hz (half wavelength) Tone burst travels as a compression wave with the speed of sound upwards in the atmosphere Wind Profiler measures the speed of propagation of the sound burst Since the speed of sound depends on the air temperature, virtual temperature can be computed from the received signal

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47 Wind profilers in Hong Kong Airport Sha Lo Wan Siu Ho Wan Sham Shui Po Cheung Chau

48 Operating modes 1299 MHz boundary layer profilers Low mode: m, 60 m range, 10 min. High mode: m, 200 m range, 10 min. Very high mode: m, 200 m range, 10 min. Data: horizontal wind, vertical velocity, signal noise ratio, spectral width

49 Applications Heavy rain NW W E 13H 7H

50 Vertical velocity W R

51 Jet stream related to heavy rain J J 22H 14H

52 Low level jet stream

53 Tropical cyclone X HK Y

54 Wind field m/s C 10 15H 8/9/96 0H 9/9/96 15H

55 Reception of World Area Forecast System (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

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

57 Thank You

58 Runway Anemometers Weather Buoys Other anemometers surrounding the airport

59 System Block Diagram for AMOS Processors and Graphical Displays