Importance of the Tropical Rainfall Measuring Mission (TRMM) Satellite to Hydrological Investigations

Rainfall over the global tropics is crucial to the global hydrological cycle and to water resources in most developing countries. Its magnitude and variations are presently poorly known. Useful global measurements can only be made from space. The Tropical Rainfall Measuring Mission satellite (TRMM) is a U.S./Japan joint space project. It carries a rain package consisting of a 14 GHz rain radar, a multichannel passive microwave radiometer, and a visible/infrared instrument. TRMM will also have a down-looking instrument to measure the upwelling short- and longwave radiation from the earth and clouds and a sensor to detect lightning. The satellite will be launched by the Japanese HII rocket in August 1997. Instrument and spacecraft progress is briefly reported. Prelaunch research is summarized, including sampling, validation and algorithm testing. It is shown that precipitation radar is essential for accurate precipitation estimates over hilly land masses, particularly during summer monsoons; thus TRMM is vital for EOS (Earth Observing System) and GEWEX (Global Energy and Water Experiment).