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CARPE DIEM

University of Essex

Anthony Holt David Bebbington Martin Fleury

Stephan Siemen + …………..

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Work packages

WP6 - Anomalous Propagation- implementation of hybrid PEM integrated with LAM

WP2 - Doppler Windfields- 3-D wind field synthesis from dual Doppler data.

Polarization Review- review of dual polarization techniques in operationalweaher radar contexts

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WP2 - Doppler Windfields

Dual Doppler Synthesis

3-D windfields may be retrieved using near simultaneously scanned Doppler from two radars in overlap away from baseline.

Dual Doppler Synthesis

3-D windfields may be retrieved using near simultaneously scanned Doppler from two radars in overlap away from baseline.

co-plane

r1 r2

u1 1

2 2

ˆ. ,

ˆ.

. 0

u r u

u r u

u

baseline

Divergence conditionenables 3-D field tobe recovered by integrationgiven boundary conditions

Divergence conditionenables 3-D field tobe recovered by integrationgiven boundary conditions

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Dual Doppler in PADRE Project

SMRSan Pietro Capofiume

CSIMTeolo (PD)

80km

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Dual Doppler Synthesis

Dual Doppler windfield sliceat 1.5 km using NCAR CEDRIC

(R.J. Watson Thesis 1996)

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WP6 - Anomalous Propagation

Anomalous propagation can create radar returns from terrain due to partial or total beam bending when strong negativerefractive gradients occur.

Apparent elevation

Actual trajectory

M(z)

z

Strong surface’reflectivity’

PRECIPor

ANAPROP?

PRECIPor

ANAPROP?

dm

s dz

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ANAPROP event from DARTH Project

25 50 75 100 125 150 175 200range, km, Azimuth 270°

50

100

150

200

250

m

100 kmRaytrace from HIRLAM model fieldspredicts RRI and position of ANAPROP

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Parabolic equation methods: PEM

‘Split-step’ parabolic equation methods allow efficient numerical solution of radar wave field in atmosphere with stratified RRI M(T,q) = 106 (m-1)

Solutions advanced between adjacent coordinate planes. Wavefront sampling

must be denseto avoid aliasing:

O(100 m)

</2 per sample

2

20 2

0

12 1

2m k

x ik z

z

Equation becomes1st order ODE inFourier zp domain:

O(1 m)

2

0

( )

( ( 1 ) ) ( )2

x x

pexp i k m x x

k

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Hybrid method: Ray/PEM

It can be shown that the methodology for the PEM applies Huyghens’principle with stationary phase integration. The constructed field closely fulfills Green’s Theorem applied to the Helmholtz equation.

It is not necessary to select coordinate planes: any series of surfacesfor which stationary phase points can be determined will do.

The hybrid method generatessurfaces orthogonal to localray trajectories - surfaces thatare very nearly parallel to thewave front.

Phase aliasing is avoided, resulting in order of magnitudereduction in wavefront sampling

The hybrid method generatessurfaces orthogonal to localray trajectories - surfaces thatare very nearly parallel to thewave front.

Phase aliasing is avoided, resulting in order of magnitudereduction in wavefront sampling

Approximate wavefront