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Validation of Propagation & Mesoscale weather models in the littoral environment: A report of the Streaky Bay Experiment Dr A.S. Kulessa Radio Frequency.

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Presentation on theme: "Validation of Propagation & Mesoscale weather models in the littoral environment: A report of the Streaky Bay Experiment Dr A.S. Kulessa Radio Frequency."— Presentation transcript:

1 Validation of Propagation & Mesoscale weather models in the littoral environment: A report of the Streaky Bay Experiment Dr A.S. Kulessa Radio Frequency Technology Group

2 Aims of the experiment  The measurement of surface & elevated duct structure in coastal environments  The modelling of sea breeze formation and resulting refractive index structure using mesoscale weather models  The validation of mesoscale weather models  The validation of PEM / hybrid propagation codes for shipboard and airborne radar / ESM ops.

3 Collaborating organisations  DSTO (EWRD)  DSTO (ISRD)  AFRL – O. Cote  Flinders University  Airborne Research Australia  CW Labs  The experiment was largely funded by the RF Hub and also by the AFRL.

4 Atmospheric mechanisms that either degrade or enhance radar/radio transmissions

5 Microwave propagation through a coastal maritime atmosphere  Streaky Bay RF propagation Experiment  The experiment featured:  Land based Emitter near Mt Westall  Airborne receiver flying between Mt Westall and Franklin Islands  Airborne Measurements of meteorological parameters – refractive index  Some mesoscale numerical weather prediction modelling

6 Mechanism for duct formation due to a sea breeze circulation  Propagation speed of sea breeze front depends on large scale forcing  Sea breeze extension depends on large off shore wind component  Onset of sea breeze depends on solar radiation available  Development of sea breeze depends also on the prevailing winds.  Duct formation; high level elevated, lower level, stronger elevated duct, surface duct.  Evaporation duct gets stronger as wind speed increases in the surface layer.  Complex refractivity structure ranging from sub – refractive over land to elevated ducts, surface ducts and “nested” ducts over the sea.

7 RF Equipment  Ground Station  Transmission parameters:fre10GHzpulse width 1  s, prf 1kHz, pol H  Transmitter: pulse generator, TWT amp, horn antenna  Power supplied by a generator  Airborne Platform: GROB G109B  Superheterodyne receiver: frequency range 2-18GHz, + horn antenna. Receiver tuned to 10GHz, measures signal pulse width and time between pulses and pulse amplitudes.  Mounted in equipment pod located under the starboard wing of the GROB G109B

8 INSTRUMENTATION AND SYSTEMs OF GROB G109B ’VH-HNK’ ParameterSensor(s)Comments position, time, attitude, accelerations Rockwell-Collins AHRS-85 Trimble TANS II GPS Trimble TANS Vector GPS Attitude System Novatel 12 Channel GPS Receiver turbulence, turbulent fluxes of sensible heat, water vapour, momentum DLR 5-hole probe under the l/h wing with two Rosemount 1221VL differential pressure sensors for air angles together with fast sensors (see below) air temperature modified NCAR k-probe (Pt100 sensor) FIAMS reverse flow probe (Pt100 sensor) modified Meteolab TP4S (thermocouple) on l/h wing pod humidity (absolute humidity and dew point) A.I.R. LA-1 Lyman-Alpha hygrometer modified Meteolab TP4S dewpoint system NOAA/ATD Infrared open-path gas analyser LiCor 6262 Infrared closed-path gas analyser inside l/h wing pod static and dynamic pressure Rosemount 1201 pressure transducer Rosemount 1221D pressure transducer inside l/h wing pod height above ground or waterKing KRA-10A radar altimeter0-800m surface temperatureHeimann KT-15 infrared radiometer4° viewing angle, 8-14nm data system data logging, real-time processing, 64 analogue channels (up to 100Hz 16 bit A/Ds), RS232/422, ARINC419/429 I/O DAMS navigation and flight guidanceGarmin GPS150 navigation computer power12VDC (25 A), 24/28VDC, 240VAC

9 Grob 109B & RF payload Operating range2-18 GHz Bandwidth40 MHz Dynamic Range< 20 dB Pulse Descriptors Amp.,PW, RF, t between pulses 10v weight3 kg Receive antennaPyramidal horn

10 Aircraft flight profile  Flights occurred between Mt Westall and the Franklin Islands  Flight pattern: Sawtooth with two ascents and two descents  Maximum height 750 metres  Minimum height 20 metres

11 Case 1: Propagation through a maritime surface duct. (Advection duct)

12 Comparison of measured refractivity profile with modelled refractivity profile  Blue curve: measured profile  Red curve: modelled profile  Model specifics:  Non-hydrostatic mesoscale  Area 120x120 km  Grid size 2x2 km  Variable vertical resolution  10 metres at the bottom –  100’s metres at the top  24 layers  Initial geostrophic wind field  Initial radiosonde ascent from nearby Ceduna  Other initial inputs: soil type, land surface temp., sea  surface temp, soil moisture content

13 Evaporation duct estimation  No direct measurement available for this experiment  Sea surface temperature + wind speed measurements were made to infer an evaporation duct model from Evaporation duct statistics collected during past experimental campaigns.

14 Coverage diagrams and propagation predictions  Tx is positioned at a height of 50m  Extended propagation is evident due to the strong surface duct (Note duct height ~ 120 – 140 metres)  Signal in the duct 10dB – 20dB stronger at distances >40km

15 Case 2: Propagation through super-refractive layers  Total flying time : 2.95 hours  Boat located midway between Mt Westall and the Franklin Islands  HNK at minimal altitude at Franklin Islands and at the boat.  One ascent and one descent between Mt Westall and the boat.  One ascent and one descent between the boat and Mt Franklin per leg.  10 legs between the boat and Mt Franklin  Maximum height of HNK: 650 metres  Minimum height : 20 metres

16 Temperature & humidity variations  Evidence for a weak temperature inversion in the second half of the run and also a dew point temperature inversion.  The wind was directed from the sea during the run.  Is it enough to produce ducting conditions ?  - super-refractive conditions ?

17 Examples of measured refractivity profiles

18 Coverage prediction

19 Measured signal level time series

20 Case 3: No temperature inversion & high humidity

21 Some conclusions  We were able to successfully establish a ground to air radio link.  We were able to measure surface duct formation due to advection off the South Australian coast  The measurements look good when compared to surface duct structure predicted from the FOOT3D mesoscale model  Comparison between TERPEM and measured signal levels looks good as well.  We measured a super-refractive atmosphere and also the corresponding propagation effects.

22 Future work  More experiments in littoral environments in order to make validation more conclusive.  - require a longer term experiment (or more short experiments) that capture different weather patterns and hence different atmospheric dynamics in the same area  - require experiments in other areas (different sea surface conditions and different land types.  Consider many realisations of mesoscale models in order to determine sensitive input parameters.  Application of Mesoscale models near the equator (i.e. tropical regions)  Validation with other data sets.  Check the modelling against data taken overseas, e.g. NZ, USA


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