C波段偏振雷达几种系统误差标定方法对比分析

Comparison among Several System Biases Calibration Methods on C- band Polarimetric Radar

通过介绍几种标定C波段偏振雷达差分反射率因子ZDR和水平反射率因子ZH系统误差常用方法的原理,利用两部相同型号的可移式C波段双线偏振雷达(POLC)在云南、安徽等地的观测数据,对这些方法进行了检验和对比分析。结果表明,ZDR的标定方法中,太阳法由于偏振雷达水平与垂直方向两个接收机在较弱的信号下很难保持一致性,目前实际应用比较困难;垂直指向法要求雷达天线必须达到90°仰角,机械上有所制约;仰角法要求探测到非常均匀的雨区,在时间与空间上极难满足;地物引起的ZDR变化,在统计上无任何规律可循,因此,地物法也基本上可以排除应用于实际;干雪的ZDR并不完全等于0 dB,并且需要知道0℃层的高度,0℃层以上满足信噪比(signal to noise ratio,SNR)条件的数据较少,并且水凝物相态难以确定为干雪,因而干雪法有着一定的局限性;微雨滴法理论清晰、结论可信,不需要专门的扫描方式,能够从正常的体扫观测中得到大量的满足SNR、ZH等阈值条件的数据,提供较为准确的ZDR系统误差估计,因此,微雨滴法是一种利用气象目标进行ZDR系统误差估计较好的方法。进一步分析ZH标定的自约束法的结果表明,自约束法能够大致地验证偏振雷达ZH标定是否正确,但是,其用于ZH标定时,对偏振参量数据质量要求较高,并且约束关系的系数也有待进一步验证。

The principles of system biases calibration of horizontal reflectivity （ZH） and differential reflectivity （ZDR） on C-band dual linear polarimetric radar are introduced. Further analysis are performed by the actual data which were detected in Yunnan and Anhui Provinces with two same type mobile C-band dual polarization radars, which were both produced by Anhui Sun-Create Electronics Co, Ltd. The results suggest that, for ZDR calibration methods, sun method is difficult to actual application as the consistency between horizontal and vertical receiver are not well in the weak signal; vertical detection one need the radar antenna can be lifted to 90° elevation angle, which has some mechanical limitation; the elevation one need a very uniform rain region which is difficult to sat- isfy; the change of ZDR caused by ground clutter have not regularity in the statistical analysis, therefore, the clut- ter calibration method is also excluded from practical application; for dry snow method, the value of ZDR of dry snow do not equal 0 dB, and the 0℃ level height need to know in advance, furthermore, the data which satisfy the requirement of SNR （signal to noise ratio） are less above the height of 0℃ level, and the phase of hydrome- teor is indefinable as dry snow, so there are certain limitation in dry snow method; micro-raindrop method can be explained clearly in theory, and the conclusion is convinced, which do not need special span mode, and can ob- tain a large number of data that satisfy the thresholds of SNR, ZH from a scan volume, therefore, micro-raindrop method is a better one to calibrate ZDR using meteorological target. After ZDR biases corrected, the feasibility of reflectivity ZH calibration by self-consistency technique is verified. The results suggest that self-consistency meth- od can approximately test the correctness of ZH calibration, however, while the method is used to calibrate ZH, high quality of polarization parameters are needed, and the coefficients in the self-consistency relationship need to be validated further more.