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The TRMM satellite carries three rain measuring instruments.NASA GSFC provided the TRMM Microwave Imager (TMI), the Visible Infrared Scanner (VIRS), and the observatory, and operates the TRMM satellite via the Tracking and Data Relay Satellite System (TDRSS). The National Space Development Agency (NASDA) of Japan (re-instituted as The Japan Aerospace Exploration Agency [JAXA] in 2003) provided the Precipitation Radar (PR), the first space-borne precipitation radar, and launched the TRMM observatory.

The TRMM orbit is circular, non-sun-synchronous, at an altitude of 350 km and an inclination of 35 degrees to the Equator.This orbit provides extensive coverage in the tropics and allows each location to be covered at a different local time each day.This kind of sampling enables the analysis of the diurnal cycle of precipitation.

The VIRS (of NOAA AVHRR heritage) is a five-channel, cross-track scanning radiometer operating at 0.63, 1.6, 3.75, 10.8, and 12 um, which provides high resolution observations on cloud coverage, cloud type, and cloud top temperatures.

The TMI (of DMSP SSM/I heritage) is a multichannel passive microwave radiometer operating at five frequencies:10.65, 19.35, 37.0, and 85.5 GHz at dual polarization and 22.235 GHz at single polarization.The TMI provides information on the integrated column precipitation content, cloud liquid water, cloud ice, rain intensity, and rainfall types (e.g., stratiform or convective).

The PR, the first of its kind in space, is an electronically scanning radar, operating at 13.8 GHz that measures the 3-D rainfall distribution over both land and ocean, and defines the layer depth of the precipitation.

There are two other TRMM instruments whose data are not archived at the Goddard DAAC.The Lightning Imaging Sensor (LIS), already tested in space, is a calibrated optical sensor operating at 0.7774 um, and it observes the distribution and variability of lightning over Earth.The Clouds and Earth's Radiant Energy System (CERES), of NASA's Earth Radiation Budget Experiment (ERBE) heritage, is a broadband scanning radiometer with a total spectral range of 0.3 to 50 um; it measures emitted and reflected radiative energy from Earth's surface and the atmosphere and its constituents (e.g., clouds, aerosols).

The instrument characteristics for the VIRS, TMI, and PR are shown in the following table:

TRMM Instrument Characteristics


 Visible Infrared Scanner TRMM Microwave ImagerPrecipitation Radar
Scanning ModeCross trackConicalCross track
Frequency/Wavelength0.63, 1.6, 3.75, 10.8, 12 um10.65, 19.35, 37.0, 85.5 GHz dual polarization, 22.235 GHz vertical polarization13.8 GHz horizontal polarization
Pre-Boost2.2 km4.4 km at 85.5 GHz4.3 km at nadir
Post-Boost2.4 km5.1 km at 85.5 GHz5.0 km at nadir
Pre-Boost720 km760 km215 km
Post-Boost833 km878 km247 km

Further Information

More detailed information about TRMM instruments is available on the TRMM Project Website.

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Last updated: Sep 09, 2009 02:27 PM ET