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WP6: Anaprop Modelling

U. Essex

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Anaprop model components• Refractivity { height, range, azimuth} from NWP data

– NWP data: temp, humidity { pressure, cartesian grid coords of polar stereographic map}

• Parabolic Equation Method propagation model– Simulated path loss { height, range } at each azimuth

• Terrain backscatter (dBZ) extraction – Function of incident intensity and wavefront angle with terrain slope

• PPI display of anaprop model and observed radar reflectivities– Simultaneous display using colour and contour plots on terrain

background

3Regions of high negative modified refractive gradient

Modified refractivity, M (r, z)

Puig Bernat Radar, Catalunya 03.00,19/07/2003Azimuth = 250 degrees

Colour palette units:Modified refractivity (ppm)

4High negative modified refractive gradient

Low path loss at terrain level at ranges of 87-91 km and 136-138 km

PEM simulated path loss

Radar elevation: 0.7 degreesRadar height: 30 metresBeam bandwidth: ~ 1 degreeFrequency: 6 GHz

Puig Bernat Radar, Catalunya 03.00,19/07/2003Azimuth = 250 degrees

Colour palette units:One way path loss (dB)

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PEM simulationAzimuth = 250o

Regions of high reflectivity at ranges of 87-91 km and 136-138 km are in good agreement with PEM simulation

Observed radar reflectivity

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Terrain backscatter (dBZ) extraction

• Terrain backscatter (dBZ) { incident intensity, wavefront angle with terrain slope}– Extract incident field from (incident + reflected)

• by filtering in elevation angle domain relative to terrain slope at each range step

– i.e. via Fourier transform of field amplitude { height}– Derive intensity and angle with terrain slope at terrain level– Apply model of radar backscattering cross section per unit area

• Function of grazing angle and surface roughness for bare soil model– Express terrain backscatter in dBZ

• by equating received radar power to that expected from raindrops in absence of anaprop

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Radar elevation: 0.7 degreesRadar height: 30 metresBeam bandwidth: ~ 1 degreeFrequency: 6 GHz

Puig Bernat Radar, Catalunya 03.00,19/07/2003Azimuth = 250 degrees

Modelled radar reflectivity

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Modelled radar reflectivity

Radar elevation: 0.7 degreesRadar height: 30 metresBeam bandwidth: ~ 1 degreeFrequency: 6 GHz

Puig Bernat Radar, Catalunya 03.00,19/07/2003

Max radar range: 250 km (20km/div)Reflectivity display range: -10 to 70 dBZ

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Observed radar reflectivity

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Modelled terrain coast

Puig Bernat Radar, Catalunya 03.00,19/07/2003

Max radar range: 250 km (20km/div)