TRMM: Tropical Rainfall Measuring Mission

The Tropical Rainfall Measuring Mission is an international research program aimed at measuring rainfall across the Earth's equatorial and subtropical regions. Ground-based weather radars have been used for decades to measure rain over limited areas. The new TRMM satellite, launched in 1997, carries the world's first radar for estimating rainfall over immense areas from space. These new observations are vitally important because, in addition to surface solar heating, the energy which drives the global winds and weather systems is primarily derived from latent heat released in rainstorms in the Earth's tropical and subtropical latitudes. An accurate understanding of global climate and of climate changes hinges in part on a quantitative knowledge of rainfall in these latitudes where ground-based measurements are sparse.

A major facet of TRMM involves surface and aircraft measurements at several locations around the globe to verify the TRMM satellite estimations of rainfall amounts. NOAA/ETL participated in these ground validation studies by operating its NOAA/D radar in Houston, Texas, in the spring of 1998. The primary objective was to apply a newly implemented polarization technique for estimating rainfall with differential phase measurements. The differential phase technique is expected to yield more accurate rain estimates than conventional radar estimates which rely solely on reflectivity data. It also has other attractive advantages, including being independent of radar calibration errors.