差分反射率因子ZDR易受雷达系统自身的影响而产生明显偏差， 这种偏差是不随空间积累而改变的。为了保证雷达资料及其产品的质量， 根据中国气象科学研究院灾害天气国家重点实验室车载C波段双线偏振多普勒雷达（C-band Polarimetric Doppler Radar on Wheel， CPDRW）的外场试验， 对观测的ZDR进行了分析， 并以垂直扫描数据的订正结果为参考， 重点讨论了以体扫模式最高仰角下的小雨和干雪这两种自然目标物为订正对象得到的订正结果。结果表明， 高仰角体扫资料的这两种自然目标物都能较好地订正ZDR的系统误差。但相较于小雨， 干雪的订正效果更加稳定， 是进行ZDR系统误差订正的最优气象目标物， 而利用高仰角体扫资料的干雪粒子进行ZDR系统误差订正也就成为垂直扫描订正法的最佳替代方法。
Differential reflectivity ZDR can have noticeable deviation which does not change with the space accumulation because of the influence of radar itself. So radar calibration is essential and critical to high quality data and products. At the present, the radar data observed at vertical incidence is commonly used to calibrate system bias of ZDR. This method, however, cannot be implemented with some radar because the antenna has elevation limit determined by the structural configuration of the antenna's pedestal. In this case, the light rain and dry aggregated snow are used as natural reflectors for ZDR calibration due to these two atmospheric scatters with low variability of intrinsic ZDR at high elevation angle and the intrinsic ZDR is close to zero. Based on the observation in field experiment by a C-band polarimetric Doppler radar on Wheel which was built in the State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences. In this paper, taking the calibration result of vertical scan data as a reference, the difference of calibration of ZDR by light rain and dry aggregated snow at the highest elevation of volume scan mode is analyzed. The results of analysis indicate that both light rain and dry aggregated snow can calibrate ZDR very well, but dry aggregated snow exhibits much lower variability of ZDR than light rain (even at high elevation) and, therefore, can be considered as the optimal weather target for calibration of ZDR. It becomes the best alternate method for system bias calibration of ZDR by vertical scan data.
[1]Seliga T A, Bringi V N. Potential use of radar differential reflectivity measurement at orthogonal polarisations for measuring precipitation[J]. J Appl Meteor, 1976, 15: 69-76.
[2]Gorgucci E, Chandrasekar V, Bringi V N, et al. Estination of raindrop sized distribution parameters from polarimetric radar measurements[J]. J Atmos Sci, 2002, 59(15): 2373-2384.
[3]Doviak R J, Bringi V N, Ryzhkov A, et al. Consideration for polarimetric upgrades to operational WER-88D radars[J]. J Atmos Ocean Technol, 2000, 17(3): 257-277.
[4]Gourley J, Kaney B, Maddox R. Evaluating the calibrations of radars: A software approach[C]. 31th Conference on Radar Meteorology, 2003: 459-462.
[5]史朝. 双极化多普勒天气雷达测量误差分析与标定研究[D]. 成都: 成都信息工程学院, 2008: 1-78.
[6]Liu Liping, Hu Zhiqun, Fang Wengui, et al. Calibration and data qualityaAnalysis withmMobile C-band polarimetric radar[J]. J Acta Meteor Sinica, 2010, 24(4): 501-509.
[7]Melnikov V M, Zrnic D S, Dovick R J, et al. Calibration and Performance Analysis of NSSL′s Polarimetric WSR-88D[R]. NOAA/NSSL Report, 2003: 77.
[8]Pratte J F, Ferraro D G. Automated solar gain calibration[C]. 24th Conference on Radar Meteorology, 1989: 619-622.
[9]Ryzhkov A V, Giangrande S E, Melnikov V M, et al. Calibration issues of dal-polarization radar measurements[J]. J Atmos Ocean Technol, 2005, 22(8): 1138-1155.
[10]Zrnic D S, Melnikov V M, Carter J K. Calibrating differential reflectivity on the WSR-88D[J]. J Atmos Ocean Technol, 2006, 23(6): 944-951.
[11]Gorgucci E, Scarchilli G, Chandrasekhar V. A procedure to calibrate multiparameter weather radar using properties of the rain medium[J]. IEEE Trans Geosci Remote Sens, 1999, 30: 269-276
[12]Bringi V N, Chandrasekar V. Polarimetric Doppler Weather Radar: Principles and Applications[M]. London: Cambridge University Press, 2001: 636.
[13]Ryzhkov A V, Zrnic D S. Discrimination between rain and snow with a polarimetric radar[J]. J Appl Meteor, 1998, 37: 1228-1240.
[14]魏洪峰, 薛震刚. 双偏振多普勒天气雷达差分反射率因子的测量误差[J]. 气象科技, 2008, 36(2): 223-227.
[15]Wang Yanting, Chandrasekar V, Bringi V N. Characterization and evaluation of hybrid polarimetric observation of precipitation[J]. J Atmos Ocean Technol, 2006, 23: 552-572.
[16]Ryzhkov A V, Zrnic D S, Burgess D, et al. Observation and classification of echoes with the polarimetric WSR-88D radar[R]. Report of National Severe Storms Laboratory, Norman, Oklahoma, 2003: 19-26.
[17]Ikeda K, Brandes E A. Freezing level determination with polarimetric radar: Retrieval model and application[C]. 31th Conference on Radar Meteorology, 2003: 649-652.
[18]刘黎平, 王致君, 徐宝祥, 等. 我国双线偏振雷达探测理论及应用研究[J]. 高原气象, 1997, 16(1): 99-104.
[19]曹俊武, 胡志群, 陈晓辉, 等. 影响双线偏振雷达相位测量精度的分析[J]. 高原气象, 2011, 30(3): 817-822.
[20]王致君, 楚荣忠. X波段双通道同时收发式多普勒偏振天气雷达[J]. 高原气象, 2007, 26(1): 135-140
[21]王致君. 偏振气象雷达发展现状及其应用潜力[J]. 高原气象, 2002, 21(5): 495-500.
[22]王致君, 楚荣忠. 偏振雷达在人工影响天气工作中的应用潜力[J]. 高原气象, 2002, 21(6): 591-598.
[23]赵果, 楚荣忠, 张彤, 等. 偏振多普勒雷达定量测量降水精度的改进[J]. 高原气象, 2011, 30(2): 498-507.
