Doppler Weather Radar Calibration Final

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Transcript of Doppler Weather Radar Calibration Final

Doppler Weather Radar CalibrationG.VISWANATHAN Director(Rtd)-ISRAD gemsvi@yahoo.com

How DWR works & what constitute the radar

DWR Calibration

data Measurement Accuracy, Precision ,Bias Radar Hardware Calibration Antenna,Rx Sensitivity, Tx Power,Signal Processing Calibration vs Validation Z estimate Validation Doppler Velocity Validation Inter comparison of data Radar-Radar, RadarGauge Networked Radars Cal/Val Issues Dual Pol Radar Calibration

R A D A R TA R G E T S

H A R D TA R G E T D i n ct sti re fl cti g e n ta rg e ts sm a l e n o u g h n o t to fi l th e l l b e a m ( Po i t ta rg e t) n R

S O FT TA R G E T D i b u te d ta rg e ts l ke h yd ro stri i m e te o rs o r tu rb u l n t m e d i m e u w h i fi l th e b e a m . ch l s ( Volume reflectivity )

3.R

Ct/2

C

/2

Radar Resolution ElementsRange : Angle :

C

/2

3.R

Doppler: 1/ T, where T is Integration Time

SPATIO TEMPORAL SAMPLING OF DYNAMIC WEATHER PHENOMENA BY DWR IN A HEMISPHERICAL VOLUME OF SPACE AROUND RADAR

3xR r 3xR= v 1 r=c/2fs

2

IPP=T=1/prf

3

Radar DataRaw Data @ I/Q level, or Signal

power received Base Data or Moment Data (Z,V, ) Derived Products, like Rain Rate(R) H Pol radars depend on emperical exponential, Z-R relationship,

BASE PRODUCTS OF THE DWR ARE THE THREE MOMENTS OF THE TIME SERIES THUS GENERATEDZ = Precipitation Intensity is the area under the curve of Doppler Velocity Spectrum for an incremental volume of space as seen by the Radar resolution elements, v=( 3 R)2( R) & filled with Hydrometeors and is estimated from the 0th moment of the Time Series generated by the radar. VD= Mean Doppler Velocity of the Hydrometeors in the resolution volume & is estimated from the First Moment of the Time Series. = Spectrum Width of Doppler Spectrum & is estimated from the Second Momentof the Time Series. where

3 = Beam width R = Range resolution R = Range to the volume elementZ

V

ISRAD

ISRO RADAR DEVELOPMENT UNIT, BANGALORE.

Accuracy, Precision, ResolutionNeither precise nor accurate Precise but not accurate

*

Accurate but not precise

Accurate & Precise

***

*** *** *** *** ***

* * * * * ***

* *

***

* *** *

A ccu ra cy

Measurement Accuracy

Frames of Reference for Radar

Zg

Tropo Centric FrameYt Xt , , h Xg N Y

Zr

= El

Target T position P(r, , ) @ t X

Origin Earth Centre Yg

= Az r = Slant range or radial distance

Geocentric Frame

(Kms) = Elevation angle [measured from local horizon (mils)] = Azimuth Angle [measured clock wise from North (mils)]

Radar Data ArrayElevation(-2 to+30deg) Azimuth for Each Elevation (0-

360deg) Range ( in terms of Range Bin) for each Azimuth Data values(say Z,V,) for each Range Bin

DWR Hardware CalibrationWeather Radar Equation relatesin terms of the System level parameters of the radar and the backscattering cross section of the target, in this case the hydrometeors in a cloud. It can be written in a simpler form as follows: Sr = KZ/(R*R) Where K is known as the Radar Constant Z is precipitation intensity in sample volume R is Slant range to Target in a given Az

the signal power received

IMD-ISRO CAL-VAL EXPERIMENT13.7Lat: 13.664 Lon: 80.227

Lat: 13.374 Lon: 80.258 Lat: 13.664 Lon: 80.227 Lat: 13.083 Lon: 80.289) g ( e d u i t a L

13.6 13.5 13.4 13.3 13.2 13.1 13 80.00 80.10 80.20 80.30CDR

SharLat: 13.374 Lon: 80.258

Lat: 13.083 Lon: 80.289

80.40

80.50

Longitude(deg)

IMD-ISRO CAL-VAL EXPERIMENT

IMD-ISRO CAL-VAL EXPERIMENT10 MHz ref DWR at SDSC SHAR Pulse/CW EXT . SIMULATOR RF source 2.7-2.9 GHz Modulator Variable Attenuator Az RJ, Cable, RF Amplifier

IF RECEIVER

RF FRONT END Cable, Az RJ Down Converter LNA P IN Directional. Coupler TRL feed

IFA & FILTER

Base band Down Conversion

I Q

2 x ADC

I Q

DSP

dBm (P OUT ) / dBZ

Figure 2. Experimental setup at DWR-SHAR for calibrating receive chain dynamic range.

IMD-ISRO CAL-VAL EXPERIMENTCDR, SHAR - LP100 90 80

Reflectivity(dBZ)

70 60 50 40 30 20 10 0 -10 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0

Input power(dBm)DWR, SHAR CDR, Chennai

IMD-ISRO CAL-VAL EXPERIMENT

The radius of the metal sphere considered in Spherecal is 15 cms. Radar cross section of this metal sphere falls close to optical region as shown in the calculations below:

IMD-ISRO CAL-VAL EXPERIMENT

. Launching of metal sphere from SHAR for spherecal experiment. Also shown I s the video output of metal sphere. Upper trace is log video and lower trace is linear output

IMD-ISRO CAL-VAL EXPERIMENT

IMD-ISRO CAL-VAL EXPERIMENT

Joint CAL-VAL Committee of IMD-ISRO

IMD-ISRO CAL-VAL EXPERIMENT

Prof.G.S,Bhat-CAOS/IISc Chairman Mr.SK.Banerji- IMD HQ Member Mr. B.Thampi IMD Member Mr.SK.Kundu- IMD HQ Member Mr.S.Venkateswarlu-IMD Member Dr.B.Manikiam-ISRO HQ Member Dr.GV.Rama- ISRO SHAR Member Mr.V.Rama Rao ISRAD Member Mr.S.Rajendran- ISRAD Member Mr.R.Ranga RaoISRAD Member-Secretary Data Analysis ably assisted by Mrs.Anitha Daniel,Subbu,&Vikas

IMD-ISRO CAL-VAL EXPERIMENTSHAR-2006_10_28_16_31_10 Comparison of PPI-Z @ Elevation 1.0 CDR-2006_10_28_16_30_29_72

SHAR22

CDR-2006_10_28_16_30_29_72

PPI (Z) comparison of SHAR and Chennai DWRs before applying the corrections

IMD-ISRO CAL-VAL EXPERIMENT2006_10_28_19_36_28 Comparison of PPI-Z @ Ele 1 CDR-2006_10_28_19_34_01

Figure 8. c)PPI (Z) comparison of SHAR and Chennai DWRs before applying the correction.

IMD-ISRO CAL-VAL EXPERIMENT2006_10_28_19_36_28 Comparison of PPI-Z @ Ele 1 after added bias +5dB to SHAR CDR-2006_10_28_19_34_01

25

SHAR

Figure 8. d)PPI (Z) comparison of SHAR and Chennai DWRs after applying the correction.

IMD-ISRO CAL-VAL EXPERIMENT

IMD-ISRO CAL-VAL EXPERIMENT

IMD-ISRO CAL-VAL EXPERIMENTScatter Figure 11. a) Scatter plot of cloud

reflectivity of SHAR and Chennai DWRs without correction. Figure 11. b) Scatter plot of cloud reflectivity of SHAR and Chennai DWRs with correction (added +2dBz to SHAR and 3dBz to Chennai data). Subsequently an inter comparison between SHAR DWR and TRMM (Joint PRTMI)revealed that SHAR DWR makes an under estimate of ~5-6dB Most likely cause is the difference in Antenna gain as measured in Test range(Without Bends& twists) & the effective gain after field installation, namely plumbing losses) In the production version of the radar WG plumbing is optimized by welding /brazing WG components with out using standard flanges etc.

IMD-ISRO CAL-VAL EXPERIMENTS tep t w otcreto c t r l _ihu o c n a o t r i6 0 5 5 5 0 CDR(Z) 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 0 5 1 0 1 5 2 0 2 5 3 0 SA( ) HR Z 3 5 4 0 4 5 5 0 5 5 6 0 y 0 82 + . 43 = . 0x 5 6 8 0

Figure 11. a) Scatter plot of cloud reflectivity of SHAR and Chennai DWRs without correction.S te p t w creto c t r l _ i ho c n a o t r i add d zo H , de - d zo D de 2Bt SA add3Bt CR R6 0 5 5 5 0CDR(Z)

4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 0 5 1 0 1 5 2 0 2 5 3 0SA( ) H Z R

y= . 82 + . 8 0 0x 0 6 8 2

3 5

4 0

4 5

5 0

5 5

6 0

Figure 11. b) Scatter plot of cloud reflectivity of SHAR and Chennai DWRs with correction (added +2dBz to SHAR and 3dBz to Chennai data).

IMD-ISRO CAL-VAL EXPERIMENTRain Acc. comparison between radar and radar DWR-SHAR 120.00 100.00 80.00 60.00 40.00 20.00 0.00 80.26 80.10 80.20 80.30 80.40 80.05 80.08 80.35 80.15 13.374 13.358 13.368 13.378 13.389 13.353 13.356 13.383 13.363 Middle points DWR-CDR Rain Acc.(mm/day)

Figure 12. Histogram of rain accumulation of both radars at equidistant locations.

IMD-ISRO CAL-VAL EXPERIMENTRain Acc. comparison between gauge and radarRaingauge 180 Rain Acc.(mm/day) 160 140 120 100 80 60 40 20 0 Sulurpet Gudur Nellore Nungambakkam Gauge locations DWR-SHAR DWR-CDR

Figure 13. Histogram of daily rainfall measured by rain gauges and DWRs.

IMD-ISRO CAL-VAL EXPERIMENT4. Conclusions For the Committee Members, visit to the radar

sites and seeing DWRs in operation was an unforgettable experience. The radar calibration experiments could be successfully carried out because IMD and ISRAD teams worked together as one unit with lot of understanding and full cooperation. This spirit should continue. Some important conclusions from calibrations carried out are as follows.

IMD-ISRO CAL-VAL EXPERIMENTSHAR_2006_10_29_05_35_28 CDR_2006_10_29_05_33_55

Figure 14.a) Radar to radar PPI (V) image comparison. (Note: The cyclone crossed Nellore. Since the cyclone is north of both the DWRs similar velocity patterns are seen by both the DWRs.

IMD-ISRO CAL-VAL EXPERIMENT The response of the receive chain sub-system of both the DWRs (forward

of the LNA input point) is linear over a dynamic range of ~100 dB. The repeatability is excellent. The performance of this sub-system is as per the design specifications. The measured radar constant based on metal sphere calibration differs from the values being used at present by +1.57 dB and +0.87 dB respectively for Chennai and SHAR DWRs. These numbers are based on the maximum value of Z measured during Spherecalexperiment at a given range of the sphere. Suncal results show that the measured antenna gain differs from the values being used at present by +1.4 dB and -0.9 dB respectively for the Chennai and SHAR DWRs. The measuremen