Validation of Propagation

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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 Technology Group

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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.

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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.

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Atmospheric mechanisms that either degrade or
enhance radar/radio transmissions
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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

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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.

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RF Equipment

• Ground Station
• Transmission parametersfre10GHzpulse width 1ms,
  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

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INSTRUMENTATION AND SYSTEMs OF GROB G109B VH-HNK INSTRUMENTATION AND SYSTEMs OF GROB G109B VH-HNK INSTRUMENTATION AND SYSTEMs OF GROB G109B VH-HNK
Parameter Sensor(s) Comments
position, time, attitude, accelerations Rockwell-Collins AHRS-85Trimble TANS II GPSTrimble 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 hygrometermodified Meteolab TP4S dewpoint systemNOAA/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 transducerRosemount 1221D pressure transducer inside l/h wing pod
height above ground or water King KRA-10A radar altimeter 0-800m
surface temperature Heimann KT-15 infrared radiometer 4 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 guidance Garmin GPS150 navigation computer  
power 12VDC (25 A), 24/28VDC, 240VAC  
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Grob 109B RF payload
Operating range 2-18 GHz
Bandwidth 40 MHz
Dynamic Range lt 20 dB
Pulse Descriptors Amp.,PW, RF, t between pulses
power 3A _at_ 10v
weight 3 kg
Receive antenna Pyramidal horn
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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

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Case 1 Propagation through a maritime surface
duct. (Advection duct)
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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
• 100s 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

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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.

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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 gt40km

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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

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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 ?

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Examples of measured refractivity profiles
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Coverage prediction
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Measured signal level time series
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Case 3 No temperature inversion high humidity
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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.

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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