NASA will decommission the Tropical Rainfall Measuring Mission (TRMM) later this year. A highly successful scientific research mission, TRMM has provided data used worldwide in the monitoring and forecasting of hazardous weather on a demonstration basis. Originally intended to be a three-year mission when launched in 1997, TRMM is now in its seventh year of operation having completed all of its research and technology objectives four years ago. The extension of mission operations for nearly four additional years was made possible through NASA's efficient management of available resources, technical innovations, and substantial additional funding.

"TRMM has been an outstanding example of scientific success and U.S.-Japanese collaboration in conducting Earth observations from space. The unique TRMM precipitation observations have led to new knowledge concerning the Earth's hydrological cycle and its variation," said NASA's Associate Administrator for Earth Science Dr. Ghassem Asrar. "We now look forward to continued cooperation with our Japanese partners on the Global Precipitation Measurement mission, that will build on the TRMM legacy," he added.

TRMM is the first mission dedicated to measuring tropical and subtropical rainfall through microwave and visible infrared sensors, including the first spaceborne rain radar. The Precipitation Radar aboard TRMM is the first rain radar ever to be launched into space. It measures precipitation distributions over both land and sea. TRMM has exceeded expectations for accuracy and resolution and has given unprecedented insights into rainfall producing cloud systems over tropical land masses and oceans.

In 1998 TRMM observed Hurricane Bonnie and captured for the first time "sky scrapper" storm clouds towering some 59,000 feet above the ocean - an event scientists believe may have represented a precursor to storm intensification.

In August 2001, TRMM was boosted from an altitude of 350 km to a higher 402 km orbit to extend its life. This maneuver successfully reduced atmospheric drag on the spacecraft during a period of high solar activity and increased TRMM's life by two years while maintaining the high quality of its scientific observations. NASA also developed a technique to extend TRMM's life by using atmospheric drag, rather than fuel, to lower the spacecraft's altitude in the early stages of the controlled de-orbit process. This scenario has permitted TRMM to continue its normal operations since November 2003.

NASA and the Japanese Space Program (JAXA) will continue close collaboration by establishing a new advanced capability for the measurement of precipitation globally with the Global Precipitation Measurement mission (GPM). The partnership will launch GPM's Core Satellite by the end of the decade.

This complex and pioneering international satellite constellation is a prototype for the comprehensive, coordinated, and sustained Earth observation system envisioned by the international Group on Earth Observations (GEO) framework. The GPM main satellite is planned to carry advanced, dual-frequency radar that will exceed the capabilities of TRMM's radar. This radar will be capable of making measurements of light rain and frozen precipitation present in higher latitudes in addition to the heavier rain present in the tropics.

In addition, GPM will comprise an international constellation of satellites to measure precipitation globally approximately every three hours; TRMM is limited to conducting less frequent observations at tropical latitudes. GPM will use an extensive ground validation network to further improve the accuracy of its measurements compared to those made by TRMM.