雷达定量估测降水的亮带自动消除改进方法

Automated correction of the bright band of weather radar reflectivity data in radar quantitative precipitation estimation

层状云降水中,0℃层融化效应会引起雷达反射率因子局部增大,若不进行订正,则会高估雷达估测的降水。本文提出一种基于新一代天气雷达反射率因子垂直廓线的0℃层亮带自动识别与订正算法,以减小因亮带造成的降水高估。本研究首先对降水类型进行分类,在SHY95的基础上增加了垂直方向的反射率因子三维特征,避免亮带的反射率因子高值区被误识别为对流云区;其次,在层状云区识别出一个可能的亮带影响区,在其中查找亮带,采用旋转坐标系法精确的识别亮带的顶、底高度;最后,利用最小二乘法拟合亮带上、下层的斜率,平滑垂直廓线(VPR,Vertical Profile of Reflectivity)的显著突出部分。将该方法应用于北京地区2010—2011年10次包含亮带的降水过程,得到的亮带订正后的均方根误差ERMS、平均绝对误差ERMA、平均相对误差BRM值较初值均有显著减小(分别减小1.538 mm,0.417和0.468)。结果表明,该方法能够有效地识别与订正亮带,使得定量测量降水精度有所提高。

In stratiform precipitation, if an appropriate correction is not applied, the bright band （BB） that is induced by melting affection will cause significant overestimation in radar quantitative precipitati- on estimation（QPE） .Therefore,the main objective of the current study is to develop an algorithm that is based on weather radar vertical profile of reflectivity（VPR） data and can automatically correct large errors caused by BB effects.Therefore ,it will improve a real-time weather radar derived QPE.Firstly, we divide radar echoes into convective and stratiform before a VPR correction is applied. In this study, in addition to the method of SHY95, we make use of a full three-dimensional volume of reflectivity characters to avoid errors caused by BB in heavy stratiform rain.Then, the stratiform area is further divided into two parts：one is the BB affected area while the other one is not.The VPR are only derived and applied to the bright band affected area （BBA） rather than to the whole radar coverage. The BB boundaries are identified by a new algorithm which utilizes a rotational coordinate system for identifying the upper and lower boundaries of BB. Finally, the slope over and under BB is obtained by a least squares linear fitting to the VPR between the BB boundaries in order to smooth the incorrect VPR curve.The correction method was tested by ten events in different seasons in Beijing from 2010 to 2011. It is found that after the correction of BB, the RMSE, RMAE and RMB of radar-gauge pairs reduce significantly （1. 538 mrn ,0. 41 and 0. 468 on average ,respectively）.So we can reach the conclusion that the correction is effective in reducing overestimation errors in radar derived QPE.