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.