The TRMM satellite, which has been collecting precipitation data flawlessly for more than five years, carries the world-first spaceborne precipitation radar. Simultaneous measurements of rain with the Precipitation Radar (PR), the TRMM Microwave Imager (TMI), and the Visible and Infrared Scanner (VIRS) onboard the satellite enable us to intercompare the data and products from three different kinds of sensors. This paper first introduces some of the achievement brought by the PR observations and issues raised by intercomparisons of PR data with the corresponding TMI data.

Based on the success of the TRMM mission, a new satellite mission called the Global Precipitation Measurement mission (GPM) was proposed. Its major objective is to measure precipitation globally and frequently so that the data can be used not only for scientific research but alto for operational applications such as weather forecasts and water resource management. It consists of the core satellite in a non-sun-synchronous orbit and a fleet of sun-synchronous constellation satellites that carry microwave radiometers. The major role of the core satellite is to provide important information of rain characteristics that can be used for accurate estimation of precipitation rate with constellation radiometers. A dual-frequency precipitation radar (DPR) is scheduled to be on the core satellite. It uses the Ku-band (13.6 GHz) and the Ka-band (35.5 GHz). The hardware characteristics of the planned DPR will be presented. New information we can extract from DPR data with a dual-frequency algorithm will also be presented. The presentation will mention some of the hardware design issues such as the pulse repetition frequency and the beam matching as well as algorithm issues such as the effect of inhomogeneous distribution of rain within the footprint in the dual-frequency rain retrieval algorithm. The characteristics of data obtained by the PR or the DPR will be compared with those of ground-based radars, and their complementary roles will be discussed.