Artist conception of the TRMM satellite.
The Tropical Rainfall Measuring Mission (TRMM) is a joint space mission between NASA and the Japan Aerospace Exploration Agency (JAXA) designed to monitor and study tropical rainfall. The term refers to both the mission itself and the satellite that the mission uses to collect data. TRMM is part of NASA's Mission to Planet Earth, a long-term, coordinated research effort to study the Earth as a global system. The satellite was launched on November 27, 1997 from the Tanegashima Space Center in Tanegashima, Japan.
Instruments aboard the TRMM 
Precipitation Radar (PR) 
The Precipitation Radar is the first spaceborne instrument designed to provide three-dimensional maps of storm structure. The measurements yield information on the intensity and distribution of the rain, on the rain type, on the storm depth and on the height at which the snow melts into rain. The estimates of the heat released into the atmosphere at different heights based on these measurements can be used to improve models of the global atmospheric circulation.
TRMM Microwave Imager (TMI) 
The TRMM Microwave Imager (TMI) is a passive microwave sensor designed to provide quantitative rainfall information over a wide swath under the TRMM satellite. By carefully measuring the minute amounts of microwave energy emitted by the Earth and its atmosphere, TMI will be able to quantify the water vapor, the cloud water, and the rainfall intensity in the atmosphere. It is a relatively small instrument that consumes little power. This, combined with the wide swath and the quantitative information regarding rainfall make TMI the "workhorse" of the rain-measuring package on Tropical Rainfall Measuring Mission.
Visible and Infrared Scanner (VIRS) 
The Visible and Infrared Scanner is one of the three instruments in the rain-measuring package and serves as a very indirect indicator of rainfall. VIRS, as its name implies, senses radiation coming up from the Earth in five spectral regions, ranging from visible to infrared, or 0.63 to 12 micrometers. VIRS is included in the primary instrument package for two reasons. First is its ability to delineate rainfall. The second, and even more important reason, is to serve as a transfer standard to other measurements that are made routinely using POES and GOES satellites. The intensity of the radiation in the various spectral regions (or bands) can be used to determine the brightness (visible and near infrared) or temperature (infrared) of the source.
Clouds and the Earth's Radiant Energy Sensor (CERES) 
CERES measures the energy at the top of the atmosphere, as well as estimates energy levels within the atmosphere and at the Earth's surface. Using information from very high resolution cloud imaging instruments on the same spacecraft, CERES also will determine cloud properties, including cloud-amount, altitude, thickness, and the size of the cloud particles. All of these measurements are critical for understanding the Earth's total climate system and improving climate prediction models.
Lightning Imaging Sensor (LIS) 
The Lightning Imaging Sensor is a small, highly sophisticated instrument that detects and locates lightning over the tropical region of the globe. The lightning detector is a compact combination of optical and electronic elements including a staring imager capable of locating and detecting lightning within individual storms. The imager's field of view allows the sensor to observe a point on the Earth or a cloud for 80 seconds, a sufficient time to estimate the flashing rate, which tells researchers whether a storm is growing or decaying.
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