垂直指向测雨雷达的误差模拟及相互校准

基于马歇尔—帕米尔(M-P)分布的雨滴谱和下落末速—降雨算法, 模拟了垂直气流和雷达垂直倾角对垂直指向测雨雷达雨强测量的影响。同时在外场, 与雨量计观测相结合, 比较了五部垂直指向测雨雷达之间的差异, 对其进行了校准。结果表明: 模拟的上升气流对雨强测量的影响大于下沉气流, 垂直气流速率越大雨强测量误差愈显著; 当雷达垂直倾角<1.5°, 或在低风速下 (水平风速<2 m/s) 且倾角<9°, 对雨强测量的影响均小于10%; 强对流性降雨过程中, 垂直气流对雨强测量的影响大于垂直倾角。另外, 通过挑选层状云降雨过程, 对比雷达与共置雨量计测量的降雨量、 对比雷达间测量的降雨量均可获取较合理的归一化斜率; 但对比雷达间测量的降雨量法更优, 利用该斜率可降低雷达间的仪器误差; 在限定雷达间反射率因子差值的条件下, 比较雷达间全部降雨过程的反射率因子也可反映仪器间的系统误差趋势。

Error Analysis and Intercalibrations of Vertically Pointing Radars on the Rainfall Measurement

The impacts of rain rates caused by the vertical wind speed and radar's vertical inclination angles were analyzed based on the relations between the falling velocity of rain drops and rainfall, and assumed Marshall-Palmer (M-P) distributions of rain drops. A field calibration of five vertically pointing radars was done under different criterions. The main results were obtained that: (1) The measured error on rain rate caused by the updraft is larger than that by the downdraft in the vertical direction. The faster the vertical velocity is, the more significant the rain rate error is.(2) The impact on measured rain rates is less than 10% when the variation range of radar's vertical inclination angle is smaller than 1.5° or when the horizontal wind speed is less than 2 m/s and the radar's vertical inclination angle is smaller than 9°. For the convective rain cases the error caused by the vertical wind is larger than that by the radar's vertical inclination angle.(3) Good normalized slopes were obtained by comparing rain rates between radars and comparing rain rate between the radars and collocated rain gauge. The method of directly comparing rain rates among radars is better than the other. The equipment errors among radars are reduced by using the normalized slopes. Similar trend can also be obtained by comparison of reflectivity factors among radars in limiting the difference of reflectivity factors.