Performance evaluation of the TRMM precipitation estimation using ground-based radars from the GPM validation network

The Global Precipitation Measurement (GPM) mission is scheduled to fly in the year of 2013 to measure the earth's precipitation structure. Since the precipitation measurement by the GPM platform will be very similar to its predecessor, the Tropical Rainfall Measuring Mission (TRMM), hence, the development of GPM algorithms to improve precipitation retrievals can be addressed through the lessons learnt from the former TRMM mission in terms of precipitation retrievals and its associated uncertainty. To support the future GPM mission, this paper assesses the performance of the TRMM precipitation estimation using ground-based radars from the GPM validation network. A total of 22 significant overpass instantaneous events from 22 different radar sites has been evaluated in view of different surface and rain type flags. The overall results show that attenuation corrected reflectivity from the TRMM precipitation radar agrees well to the measured reflectivity from ground based radars with correlation coefficients r=0.91 (without frequency adjustment) and r=0.92 (with frequency adjustment). However, the correlation decreases by 10-30%, once the reflectivity are transformed to rainfall rates. The lower correlations on the basis of precipitation estimation by the TRMM are exhibited over the coast than those of ocean and land surface terrain. Taking into account the rain type flags, the analysis shows a poor correlation during convective precipitations, in particular, those retrieved from the TRMM precipitation radar. In contrast, the combined algorithm, which utilizes both radar and microwave imager instrument on-board TRMM, outperforms throughout the analysis, yet, there is a scope to improve the precipitation retrievals. (C) 2012 Elsevier Ltd. All rights reserved.