Bangkok, Thailand, 5-13 February 2018

WMO/ASEAN Training Workshop on Weather Radar Data Quality and Standardization

Japan Meteorological Agency

Calibration of dual-pol data

7 February 2018

Hiroshi Yamauchi Observation Department

Japan Meteorological Agency

Bangkok, Thailand, 5-13 February 2018

WMO/ASEAN Training Workshop on Weather Radar Data Quality and Standardization

Japan Meteorological Agency

• Required accuracy for dual-pol

• Calibration of Z (absolute calibration)

• Calibration of Zdr and Fdp

• rhv correction to mitigate effect of noise

Contents

Required accuracy for dual-pol

■CIMO GUIDE

3

■NEXRAD (Ryzhkov et al. 2005)

■NOAA/National Weather Service Radar Functional Requirements (2015)

Error = random error + systematic error (bias)

Bias of Z ±1 (dB)

Bias of ZDR ±0.1~0.2 (dB) very high accuracy!!

Causes of Z bias

4

Tx

AZ RJ

EL RJ

Rx TR

Transmitting Loss: Lt [dB]

Antenna Gain: G [dB]

DC

Radome Loss [dB]

Receiving Loss: Lr [dB]

ZLrLt

e

2

22

2

t

10

3

r 2

1

r

1GP

2log2

c P

Radar equation

r

2

2

2

t

2

3

10

P 2

1 r

GPc

2log2

LrLtZ e

Errors in hardware parameters cause bias in Z.

Measurement errors of hardware parameters

Mistakes in setting of radar parameters

Changes with age

Calibration of Z is called “absolute calibration.”

Pt

Pr

Calibration of Z

Using metal sphere

Using external receiver and transmitter

Using disdrometer

Using rain-gauges

Self-consistency

5

Adachi et al. 2015: Estimation of Raindrop Size Distribution and Rainfall Rate from Polarimetric Radar Measurements at Attenuating Frequency Based on the Self-Consistency Principle

Using External Receiver and Transmitter

6

r

r

Lr

Using Disdrometer

7 Courtesy of Mr. Umehara

radar Disdrometer

Both radar and disdrometer observe Z

time Re

fle

ctivity Z

[ d

BZ

]

Using rain-gauges

8

Assuming Z-R relations (B, b)

Derive bias as a ratio between accumulative rain-amount observed by rain-gauges and that estimated by radar.

N

i

i

N

i

i

N

N

1

1

1

1

A

R

GbBR Z

ZA Z -

corr

bb

1

B

Z R

cv cv cv

Bias Z-R relation

Steiner et al, 1999: Effect of bias adjustment and rain gauge data quality control on radar rain fall estimation. Water Resour. Res., 35, 2487-2503.

Bias correction

Using rain-gauges

9

b

1

B

Z R

b

1

corr

B

Z R

After correction

Causes of Zdr and Fdp bias

10

Difference of Tx power, Rx sensitivity, losses between H and V result in Zdr bias.

Difference of path length between H and V result in Fdp bias.

Pt_H Tx_H Tx_V

AZ RJ

EL RJ

EL RJ

Rx V

Rx H

TR

TR

Lt_H

DC

DC

Lr_H

Lt_V

Lr_V

Pr_H

Pr_V

Pt_V

Using metal sphere

Bird-bath scan (PPI scan at el=90°)

Using drizzle or light rain

Using solar signals (only for Receiver bias)

11

Calibration of Zdr and Fdp

Fdp (deg)

Zdr(dB)

Z(dBZ)

Bird-bath scan

From upward view, even a large rain drop looks circle

RHI

RHI

RHI

12

Side view H>V

Upward view H=V

High Gain: -0.2deg Low Gain: -0.2deg

Stratiform rain

ZDR EL =90 deg Azimuthal-mean

Bird-bath scan

Useful in estimating Zdr bias and Φdp bias

Zdr and Φdp must be zero

Side view H>V

Upward view H=V

360°

13 Courtesy of Mr. Umehara

rhv correction to mitigate effect of noise

14

21

00

0

vvhh

hv

hvRR

Rr

N

n

vhvhvhvh

N

n

hvhv nInQnQnIinQnQnInIN

nVnVN

R ])[][][][(])[][][][(1

][][1 *

0

])[][(1

][][1 22*

0 nQnIN

nVnVN

R h

N

n

h

N

n

hhhh

])[][(1

][][1 22*

0 nQnIN

nVnVN

R v

N

n

v

N

n

vvvv

Auto correlation for H signal

Cross correlation between H and V

Where,

21

00

0

vvvhhh

hv

hvNRNR

R

r

Subtract noise level NnnQinInV hhh ...1][][][

NnnQinInV vvv ...1][][][

Auto correlation for V signal

correction

The method which does not depend on noise level estimation is also proposed. Cheong et al. 2013: The impacts of multi-lag moment processor on a solid-state polarimetric weather radar

Summary

High accuracy is needed for dual-pol data to make use of

them.

Calibration of Z (absolute calibration)

Calibration of Zdr and Fdp

rhv correction is needed to mitigate effect of noise

More information will be available via DWD HP of Weather

Radar Calibration & Monitoring workshop 2017

https://www.dwd.de/EN/specialusers/research_education/

seminar/2017/wxrcalmon2017/wxrcalmon_en_node.html

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