Global mapping of the rainfall from a system of spaceborne rain radars

Measuring precipitation on the global scale is of major interest for climate research. It is admitted that the only way to map precipitation on the global scale is the observation from space. However the passive techniques presently available (infrared, visible, or microwave) are limited. The Tropical Rainfall Measurement Mission (TRMM) jointly realised by NASA and NASDA will be the first space platform associating a rain radar and a microwave radiometer. Hopefully, TRMM will be the first of a series of mission devoted to the global survey of the rainfall. The present paper aims to examine what improvements it would be worth to bring in the next missions. It covers in particular the following aspects: (i) Which radar technique and algorithm is the most performant, in terms of accuracy of the rain retrieval? (ii) What should be done to enlarge the radar swath? (iii) What type of future mission could improve the sampling operated by TRMM?