validation of propagation & mesoscale weather models in the littoral environment: a report of...
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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
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.
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.
Atmospheric mechanisms that either degrade or enhance radar/radio transmissions
PHYSICAL MECHANISM
SCALE REGIONS HEIGHT OF OCCURENCE
MODELS
Radiative heating
Meso / macro Land, desert Surface – thousands of feet
Numerical weather models
Radiative cooling
Meso / macro Desert, dry – inland, prairie
Surface – hundreds of feet
Numerical – analytical weather models
evaporation macro sea Surface – 200 feet
Empirical models; databases
advection meso Coastal, land & sea
Hundreds – thousands of feet
Circulation models, numerical weather models
subsidence meso Coastal, sea Thousands of feet
Numerical weather models
subsidence macro Land and sea Thousands of feet, Boundary layer & above
Numerical weather models
Frontal system meso Land and sea Hundreds – thousands of feet
Numerical weather models
Upper – air turbulence
macro Land and sea Thousands & tens of thousands of feet
Direct measurements of turbulence
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
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.
RF Equipment
Ground Station Transmission
parameters:fre10GHzpulse width 1s, 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
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
Grob 109B & RF payload
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-75 -73 -71 -69 -67 -65 -63 -61 -59 -57 -55 -53 -51 -49 -47 -45
Input Power (dBm)
Cold
Warm
Operating range
2-18 GHz
Bandwidth 40 MHz
Dynamic Range
< 20 dB
Pulse Descriptors
Amp.,PW, RF, t between pulses
power 3A @ 10v
weight 3 kg
Receive antenna
Pyramidal horn
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
Case 1: Propagation through a maritime surface duct. (Advection duct)
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
320 330 340 350 360 370 380 390
Modified Refractity (M)
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igh
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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.
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
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(dB)path loss1-w ay
0 10 20 30 40 50 60 70 80 90 100Range, km
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StB10022002.fld
-100 -90 -80 -70 -60 -50 -40
signal level (dBm)
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heig
ht (
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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
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 ?
Examples of measured refractivity profiles
Coverage prediction
Measured signal level time series
Case 3: No temperature inversion & high humidity
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.
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