The Tropical Rainfall Measuring Mission's (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 is able to quantify the water vapor, the cloud water, and the rainfall intensity in the atmosphere.

Objectives

Before TRMM's launch measurements of the global distribution of rainfall at the Earth's surface had uncertainties of the order of 50% and the global distribution of vertical profiles of precipitation was far less well determined. TRMM is providing some of the first spaceborne rain radar and microwave radiometric data that will measure the vertical distribution of precipitation over the tropics in a band between 35 degrees north and south latitudes. Such information will greatly enhance our understanding of the interactions between the sea, air and land masses which produce changes in global rainfall and climate. TRMM observations will also help improve modeling of tropical rainfall processes and their influence on global circulation leading to better predictions of rainfall and its variability at various time scales.

Instrument

TMI is not a new instrument. It is based on the design of the highly successful Special Sensor Microwave/Imager (SSM/I) which has been flying continuously on Defense Meteorological Satellites since 1987. The TMI measures the intensity of radiation at five separate frequencies: 10.7, 19.4, 21.3, 37, 85.5 GHz. These frequencies are similar to those of the SSM/I, except that TMI has the additional 10.7 GHz channel designed to provide a more-linear response for the high rainfall rates common in tropical rainfall. The other main improvement that is expected from TMI is due to the improved ground resolution. This improvement, however, is not the result of any instrument improvements, but rather a function of the lower altitude of TRMM 250 miles (402 kilometers) compared to 537 miles (860 kilometers) of SSM/I). TMI has a 547 mile (878-kilometer) wide swath on the surface. The higher resolution of TMI on TRMM, as well as the additional 10.7 GHz frequency, makes TMI a better instrument than its predecessors. The additional
information supplied by the Precipitation Radar further helps to improve algorithms. The improved rainfall products over a wide swath will serve both TRMM as well as the continuing measurements being made by the SSM/I and radiometers flying on the NASA's EOS-PM and the Japanese ADEOS-II satellites.

Data Access

All TRMM products are archived and distributed by the Goddard Distributed Active Archive Center (DAAC) and its subcenter under TRMM data access page. For further information concerning TSDIS operations go to ths TSDIS homepage.

TMI quick-looks available on-line. Each quick-look is generated at a resolution of 1/4 degree, thus generating an image of 1440x720 pixels.

The TRMM Platform

TRMM is NASA's first mission dedicated to observing and understanding the tropical rainfall and how this rainfall affects the global climate. The joint mission with the National Space Development Agency of Japan was launched on Nov. 27, 1997, from the Japanese Space Center, Tanegashima, Japan, and has produced continuous data since Dec. 8, 1997. The primary rainfall instruments on TRMM are the TRMM Microwave Imager (TMI), the precipitation radar (PR), and the Visible and Infrared Radiometer System (VIRS). Additionally, TRMM carries the Lightning Imaging Sensor (LIS) and the Clouds and the Earth's Radiant Energy System Instrument (CERES). These instruments can all function individually or in combination with one another. TRMM is part of NASA's Mission to Planet Earth, a long-term, coordinated research effort to study the Earth as a global system.

Links

• The Goddard DAAC TRMM Information Page
• The NASA (US) TRMM home page
• The JAXA (Japanese) TRMM home page

Contact

If you would like to have more information about the TMI data, please contact wdc@dlr.de.