Research On Calibration Of Dual-polarized Weather Radar And Scheme For Inspection Of Polarization Parameter At Low SNR

Dual polarization is becoming the standard of new weather radar system. In contrast to conventional weather radar, dual polarity weather radar transmits and receives both horizontal and vertical polarized signals, which significantly improves the accuracy of radar-based rainfall measurements and enhances the ability to classify precipitation. However, the measuring result will be affected by the radar system itself. The differential reflectivity ZDR can be estimated imprecisely which results in a decrease of the reliability of generated meteorological products.To obtain an accurate ZDR so that to guarantee a high measuring quality of dual polarity weather radar system, the National Weather Service made a large number of experiments on upgraded WSR-88D radars and found that it is necessary to straighten the deviation made by signal differences in both transmit and receive paths. After plenty of experiments on the C-band dual polarity vehicle Doppler radar and comparing the result to United States WSR-88D test report, this paper reaches a conclusion that bias of the ZDR calibration consists mostly of 3 components which are transmit bias, receive bias and Sun measurement bias. The bias can be adjusted by using cross and parallel method to eliminate effects of test signals, cables and other equipments’differences. Furthermore, dry aggregated snow is considered as an optimal weather target for the calibration of the ZDR.The following of this paper will illustrate the research of the relationship between the ZDR, the correlation coefficient and noise-signal ratio. The result of the research is calculated by using an external CW calibrated generator which injects different signal powers from very weak to strong signals connected to the coupler ports. In conclusion, the ZDR and p will be noticeably biased if signal-to-noise ratio (SNR) is less than 20 dB. At last, the ZDR is corrected, especially for light rain, snow, and clear-air echoes caused by biological scatters. Consequently, this paper shows that the calibration method is an effective and practical way to strengthen system bias of the ZDR so that to ensure the precision of dual polarization radar system.