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A Method for Calibrating Zdr by Using Light Rain Echo in Volume Scan Data

In 2019 CMA is still working on upgrading the weather radars to dual polarization as scheduled, dozens of polarimetric radar have been deployed and put into operation, but proper ZDR bias calibration procedures for operational radar are still absent. The accuracy of quantitative precipitation estimators(QPE) and hydrometeor classification algorithm depends heavily on the accurate estimation of ZDR. Continuously monitoring and measurement of system ZDR bias is the key calibration technique for polarization radar, and it’s also one of the biggest challenges in radar operation and maintenance. In order to solve the key technical problems of ZDR calibration for operational radar, this paper proposes a method of ZDR deviation monitoring and calibration using light rain echoes from volume scan data. Both theorical analysis and observation prove that the intrinsic ZDR of light rain is between 0.25-0.35dB. We select light rain echo from every volume scan filtered by range, elevation, signal-to-noise ratio(SNR), correlation coefficient(phv) and the melting layer height.After several volume scans, the system ZDR bias is estimated and calibrated in real time through statistical analysis of light rain ZDR distribution mode. Two precipitation processes in 2016 and 2017 are used to verify and evaluate this method, we can conclude from the test data: (1) the histogram of ZDR is more reasonable after filtered. With the change of ZDR, the change of sample data is close to normal distribution, which proves the rationality of data screening.(2) the system bias ZDR estimated from two precipitation processes is between 0.3-0.5dB, the 0.2dB error meets the accuracy requirements of ZDR (0.1-0.2dB).(3) The new method can estimate and calibrate the ZDR bias along with routing volume scan, which is suitable for operational radar.