基于GPM卫星双频降水雷达的地面降雪识别算法

Surface snowfall identification algorithm based on GPM-DPR observations

继搭载在TRMM(Tropical Rainfall Measuring Mission)卫星上的降水雷达PR(Precipitation Radar)之后,GPM(Global Precipitation Measurement)核心观测平台搭载了全球首个双频降水雷达DPR(Dual-Frequency Precipitation Radar),其对降雪的探测能力备受人们关注.本文基于GPM双频降水雷达的探测数据,以三次降水过程(包含降雪、积层混合性降雨和冬季层状云降雨)为例,利用Ku和Ka双波段三个参量(即测量双频比DFRm垂直廓线斜率、回波顶高、垂直方向上Ku波段最大反射率因子)计算的降雪指数SI(Snow Index)来识别地面降水相态.结果表明,若不使用辅助信息(0℃等温线高度等),利用SI原计算公式能很好地区分夏季降雨和降雪,但较难区分冬季降雨和降雪.为了提高冬季降雨和降雪的分辨效果,改进了反射率因子的质量控制方法,用最小二乘法计算DFRm垂直廓线的斜率,结果显示改进后地面降雪识别结果与地面自动站观测结果有较好的一致性.

Following the PR(Precipitation Radar)on the TRMM(Tropical Rainfall Measuring Mission)satellite,The GPM(Global Precipitation Measurement)core observatory carries the first spaceborne Dual-frequency Precipitation Radar(DPR),operating at Ku and Ka bands(13 and 35 GHz,respectively).Its ability to detect snowfall has attracted much attention.Based on DPR observations,this paper uses a Snow Index(SI)algorithm to identify surface precipitation phases taking three processes that occurred in China as examples,including snowfall,summer mixed rainfall and winter stratiform rainfall.SI is calculated using three ingredients of DFRm slope,maximum value of reflectivity at Ku-band,as well as storm top height.It is found that if the auxiliary information(0℃isotherm height,etc.)is not used,it is easy to identify summer rainfall and snowfall using the original SI formula,but difficult to identify winter rainfall and snowfall.Therefore,the quality control method of reflectivity factor is improved and the slope of DFRm vertical profile is calculated by the least square method.The results show that the identification results of the improved method are in good agreement with the ground automatic station observation data.