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

0

50

100

150

200

250

300

350

400

450

500

550

-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)

0

100

200

300

400

500

600

He

igh

t (m

)

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

110

115

120

125

130

135

140

145

150

155

(dB)path loss1-w ay

0 10 20 30 40 50 60 70 80 90 100Range, km

0

50

100

150

200

250

300

350

400

450

500Height, m

StB10022002.fld

-100 -90 -80 -70 -60 -50 -40

signal level (dBm)

0

100

200

300

400

500

heig

ht (

m)

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