广州S波段双偏振雷达数据质量初步分析

广东省已经通过新布设或对CINRAD\SA雷达的升级改造完成5部S波段双偏振雷达的业务运行。受目前双偏振雷达技术水平限制，双偏振雷达偏振量很不稳定，因此偏振雷达资料使用前需要对数据可用性、偏振量的系统偏差等进行初步分析，以保证偏振雷达后续产品的可靠性。使用广州S波段双偏振雷达稳定运行后的2016年7—8月连续观测资料，分析了噪声对零滞后相关系数ρ_HV(0)及差分反射率因子Z_DR的影响和订正效果。结果表明:当SNR小于20.0 dB时，偏振参量ρ_HV(0)和Z_DR的稳定性变差，数据不可用；噪声订正后，数据可用的SNR阈值减小为17.0 dB。进一步分析了经过噪声订正后的Z_DR和Z_H之间的关系，并与雨滴谱反演结果及理论值进行对比。结果表明:广州雷达Z_DR较雨滴谱反演值和理论值均偏小，Z_DR观测值存在系统偏差。结合广州的气候特征，对偏振量系统误差估计的微雨滴法的指数进行了调整，基于此方法分析了Z_DR、初始相位Φ_DP (0)的系统误差随方位角的变化。结果表明:Z_DR系统误差随方位角在-0.29~0.22 dB之间波动，剔除遮挡后的平均偏差为-0.09 dB，与实测Z_DR值和雨滴谱反演值及理论值对比偏小的结论一致，但偏差大小有区别；同时，Φ_DP (0)随方位角有4 °左右的波动。分析还发现Z_DR、Φ_DP (0)系统误差有随时间波动的特征。最后挑选个例对Z_DR进行噪声和系统误差订正后发现，订正后的Z_DR得到改善。这些初步分析和结果对S波段双偏振雷达数据的使用有一定的参考意义。 

PRELIMINARY ANALYSIS OF DATA QUALITY OF GUANGZHOU S-BANDPOLARIMETRIC WEATHER RADAR

At present, there are five S-band polarimetric weather radars operating in Guangdong province. Due to the technical limitation of the current polarimetric weather radars, the raw polarimetric variables are still unstable, andthe data availability and the main influencing factors must be analyzed in order to ensure the reliability of radar products. Based on the continuous observation data of the dual polarization radar in Guangzhoufrom July to August in 2016, the effects of signal-to-noise ratios (SNR) on cross-correlation coefficients at zero lag (ρ_HV (0)) and differential reflectivity (Z_DR) were analyzed.The result shows that only when SNR reaches 20.0 dB or above, the radar data is credible, and the SNR threshold value of the data can be decreased to 17.0 dB after noise correction. The relation between reflectivity (Z_H) and Z_DR after noise correction was also analyzed and compared with the fitting results of the raindrops spectrum and the simulated data. The result shows that the measured value of Z_DR of a polarimetricradar in Guangzhou is less than both of the fitting results and the simulated data. After the micro-raindrop method index was adjustedaccording to the climatic characteristics of Guangdong, the system bias of Z_DR, initial differential phase(Φ_DP(0)) with the different azimuth and time were further analyzed. It is found that Z_DR fluctuates between -0.29 dB and -0.22 dB with the azimuth, the average deviation is -0.09 dB after excluding theblockage; and Φ_DP(0) fluctuates about 4 ° with the azimuth, and the system biases of Z_DR, Φ_DP(0) fluctuatewith time obviously. In the end, the Z_DR was corrected in terms of noise and system biases, and the result shows the quality of Z_DR has been improved. These preliminary results are useful for polarization radar data applications.