Reliable global quantitative precipitation measurement is critically important for a variety of applications, including flood forecasting, numerical weather prediction, understanding the evolution of hurricanes and severe storms, and tracking of long-term trends in global precipitation and water supply. When combined with comprehensive ground validation and calibration, satellite observations offer practical prospects for acquiring accurate and global datasets especially over oceans and remote regions. Since the advent of satellite sensing of clouds and precipitation there has been much progress in terms of instrumentation and algorithm development. The Tropical Rainfall Measuring Mission (TRMM), launched in 1997, represents an advanced active and passive remote sensing system to measure precipitation. Each precipitation satellite mission requires thorough ground validation to test instrument and algorithm performance. With the success of the TRMM and the plans for TRMM's successor mission, the Global Precipitation Measurement mission (GPM), the current era represents •