III) CHARACTERISTICS OF THE ADDED CLUTTER RAIN MeteoSvizzera, 6605 Locarno, Switzerlandemail:...

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III) CHARACTERISTICS III) CHARACTERISTICS

OF THE ADDED OF THE ADDED CLUTTERCLUTTER

Horizontal ph

ase angle ( O)

tal re

70.5 71.0 71.5 72.0 72.5 73.0Azimuth (O)

tal re

Horizontal ph

ase angle ( O)

tal re

Horizontal ph

ase angle ( O)

52.0 52.5 53.0 53.5 54.0 54.5Azimuth (O)

tal re

) Horizontal ph

ase angle ( O)

RainRAIN

MeteoSvizzera, 6605 Locarno, Switzerland email: Katja.Friedrich@meteoswiss.ch http://www.meteoswiss.ch

Simulation of Ground Clutter Influence on Polarimetric Rainfall RateKatja Friedrich*, Urs Germann*, Gianmario Galli*, Pierre Tabary+, Jacques Parent du Chatelet+

*MeteoSwiss, Locarno, Switzerland; +Météo France, Paris, France

MOTIVATIONMOTIVATIONHow sensitive is the polarimetric rainfall rate estimation to ground clutter contamination when the clutter intensity is as large as or smaller than that of rain? We investigate the sensitivity of quantitative precipitation estimation during stratiform precipitation in the presence of strong and weak clutter contamination caused by obstacles such as mountains, buildings, trees, power lines.

IDEAIDEA REALIZATIONREALIZATION- - Take I/Q time series of clutter and rain measured by the Météo France

C-band polarimetric Doppler radar located ~30 km southwest of Paris - - Create a mask representing the location of rain based on thresholds- - Select I/Q time series of point targets (Eiffeltower) and more complex

clutter targets with different polarimetric characteristics- - Add continuously the signatures of along the range to observed I/Q

time series of rain for an entire scan; repeat this by reducing the power of clutter signals step by step until its median in reflectivity is < 0.3 dBZ; determine the critical level of clutter signal for polarimetic rainfall rate estimation

Distance /azimuthal

range (km/°)

(dB)hv dp

Rain 76.8 / 3.0 32.9 (32.9)

0.4 0.99 8.3

B1 24.0 / 0.5 55.5 (67.9)

4.9 0.96 51.1

B2 24.0 / 3.0 49.2 (61.6)

7.3 0.96 56.8

B3 3.8 / 3.5 28.5 (56.8)

-4.4 0.30 43.4

B4 20.9 / 2.5 25.6 (39.2)

-3.7 0.87 123.4

B5 0.7 / 2.5 96.7 (33.8)

0.5 0.94 -5.9

B6 1.4 / 2.5 89.9 (33.1)

-3.2 0.91 132.8

B7 1.68 / 2.5 86.8 (31.3)

-0.9 0.53 -11.2

B8 1.92 / 2.5 83.9 (29.6)

-1.2 0.33 12.4

B9 23.8 / 2.5 29.9 (0.4) 5.3 0.81 126.1

IV) REFERENCE FIELDS + ADDED CLUTTER =IV) REFERENCE FIELDS + ADDED CLUTTER =

CONCLUSIONS CONCLUSIONS based on the based on the 15-Nov15-Nov-case-case & OUTLOOK & OUTLOOK

I) REFERENCE FIELDS – STATIFORM PRECIPIATION ON 15 NOVEMBER 2005 AT I) REFERENCE FIELDS – STATIFORM PRECIPIATION ON 15 NOVEMBER 2005 AT 1456 UTC1456 UTC

Zh = 30.26 dBZ Zdr = 0.37 dB dp = 7.74° hv = 0.98

R(Zh,Zdr) = 3.1 mm h-1R(Zh ) = 2.0 mm h-

R(Zh) = 0.0034 Zh0.6024 R(Zh, Zdr) = 0.0221 Zh

0.76 10-0.33Zdr

B266.5 67.0 67.5 68.0

Azimuth (O)

Horizontal ph

ase angle ( O)

Horizontal ph

ase angle ( O)

66.5 67.0 67.5 68.0Azimuth (O)

Horizontal ph

ase angle ( O)

66.5 67.0 67.5 68.0Azimuth (O)

Horizontal ph

ase angle ( O)

66.5 67.0 67.5 68.0Azimuth (O)

Horizontal ph

ase angle ( O)

Zdr (dB) R(Zh) (mm h-1)

b) -30 dBZ

R(ZhZdr) (mm h-1)

2.) Reduced power of the clutter signal versus differences between (reference fields + added clutter) and reference fields for B1 – B9:

a) -13 dBZ

1.) Reference fields (rain) versus reference fields+B1 (rain+clutter) when the median of [Zh(clutter) – Zh(rain)] is:

1a) -13 dBZ

1b) -30 dBZZh (dBZ)

dp (°)-13 dBZ

-30 dBZ

Median Zh (dBZ) Median Zdr (dB)

Median dp (°)Assuming theoretical accuracies as shown in

(black, horizontal lines), the critical level of clutter contamination for polarimetric parameters (black, vertical lines) is achieved when the clutter signal is:

♪ 6 – 11 dBZ lower than that of rain for Zh

♪ 7 – 20 dBZ lower than that of rain for Zdr

♪ 10 – 26 dBZ lower than that of rain for hv

♪ 6 – 23 dBZ lower than that of rain for dp

Variability of the critical level

accuracy

Assuming an theoretical accuracy in rain rate of

~10 %, the critical level for rainfall rate estimation is achieved when the clutter signal is:

♪ 7 – 13 dBZ lower than that of rain for R(Zh)♪ 6 – 24 dBZ lower than that of rain for

R(Zh,Zdr)Polarimetric variables and R(Zh,Zdr) are more sensitive to small amounts of ground clutter but also have a larger variability of the critical level compared to Zh and R(Zh)

II) RAIN II) RAIN MASKMASK

25 < Range < 100 km

15 < Zh < 50 dBZTexture(Zdr) < 1.50

dB0 < Zdr < 4 dBhv > 0.97dp < 20°Beam shielding < 50

3.3.2.2.

4.4.4.1.4.1.

Zh (dBZ) Zdr (dB) dp (°)

hvR(Zh ) (mm h-1)

R(Zh,Zdr )

(mm h-1)

Ground clutter

dp (rain) (°)R(Zh,Zdr) (rain) (mm h-1)R(Zh) (rain) (mm h-1)Zdr(rain) (dB)Zh(rain) (dBZ)

4.1.1.4.1.1.

4.1.2.4.1.2.

4.1.1.4.1.1.

4.1.2.4.1.2.

4.2.4.2.

Measure in-phase (I) & quadrature (Q) signals in clear air and rainAdd I/Q time series measured in clutter to I/Q time series of rain Process data, calculate polarimetric variables (Zh, Zdr, hv, dp), apply a quality control, estimate the rain rate R(Zh), R(Zh, Zdr) Compare results

0.1 dB

Median R(Zh) (mm h-1)

~10 % (0.2 mm h-1)

Median R(ZhZdr) (mm h-1)

Median hv

~10 % (0.3 mm h-1)

These results need to be verified by more cases with different rain rates and drop size distributions and the accuracy of R(Kdp), R(Kdp, Zdr) needs to be included.

35.0 36.0 37.0 38.0Azimuth (°)

hv (ra

Zh(clutter) – Zh(rain) (dBZ) Zh(clutter) – Zh(rain) (dBZ)

III) CHARACTERISTICS OF THE ADDED CLUTTER RAIN MeteoSvizzera, 6605 Locarno, Switzerlandemail:...

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