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.