Privacy, Security, Notices

Overview:

The Tropical Rainfall Measuring Mission (TRMM) is the first mission dedicated to measuring tropical and subtropical rainfall through microwave and visible infrared sensors, and includes the first spaceborne rain radar.

Tropical rainfall comprises more than two-thirds of global rainfall. It is the primary distributor of heat through the circulation of the atmosphere. Understanding rainfall and its variability is crucial to understanding and predicting global climate change. Our current knowledge of rainfall is poor, especially over the oceans. By use of a low-altitude orbit of 217 miles (350 kilometers), TRMM's complement of state-of-the-art instruments will provide more accurate measurements. These new measurements will increase our knowledge of how rainfall releases heat energy to drive atmospheric circulation.

TRMM's orbit will range between 35 degrees north and 35 degrees south of the equator, allowing TRMM to fly over each position on the Earth's surface at a different local time each day. Scientist can use data from this kind of orbit to calculate rain variations over a 24-hour period; the result will be a data set vastly more informative than any now available

TRMM is a joint project between the United States and Japan. The Japan Aerospace Exploration Agency (JAXA) will provide the Precipitation Radar (PR) and an H-II rocket planned to launch the TRMM observatory in the fall 1997 for a 3-year mission. NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Maryland, will provide the observatory, four instruments, integration and test of the observatory, the science data processing system, and will operator the TRMM satellite via the Tracking and Data Relay Satellite System (TDRSS).

TRMM Science Objectives

1. To obtain and study multiyear science data sets of tropical and subtropical rainfall measures;

2. To understand how interactions between the sea, air, and land masses produce changes in global rainfall and climate;

3. To improve modeling of tropical rainfall processes and their influence on global circulation in order to predict rainfall and variability at various period of time; and

4. To test, evaluate, and improve satellite rainfall measurement techniques.

TRMM Observatory and Instruments

GSFC will design, build and test the observatory "in house" at its Greenbelt, Maryland facility. At launch, the observatory will weigh 7,290 lbs (3,600 kg). It is about 17 feet tall (approximately 5 meters) and 12 feet (3.6 meters) in diameter. A gallium arsenide solar array/nickel cadmium battery power subsystem will provide 1,100 watts of load power to the satellite.

A three-axis attitude control subsystem will stabilize the observatory and keep the instruments pointing toward Earth to within 0.2 degrees. A command and data handling subsystem will provide onboard commanding, data collection, processing and storage. This subsystem will use state-of-the-art technology employing a fiber optic data bus and solid state recorders.

A reaction control subsystem will maintain the orbit at approximately 217 miles (350 km). Data for each orbit will be stored on board and transmitted to the ground by the communication subsystem through TDRSS once per orbit. The observatory instruments for primary rainfall measurements are a precipitation radar, a multifrequency microwave radiometer and a visible/infrared radiometer. For observations related to precipitation, NASA has added a Lightning Imaging Sensor (LIS) and a Clouds and the Earth's Radiant Energy System (CERES). A brief description of the five instruments follow:

• The Precipitation Radar (PR) will determine the vertical distribution of precipitation by measuring the "radar reflectivity" of the cloud system and the weakening of a signal as it passes through the precipitation. A unique feature of the PR is the measurement of rain over land, where passive microwave channels have more difficulty.

• The TRMM Microwave Imager (TMI) is a multichannel radiometer, whose signals in combination can measure rainfall quite accurately over oceans and somewhat less accurately over the land. The TMI and PR data will yield the primary precipitation data sets.

• The Visible Infrared Scanner (VIRS) measures radiance in five bandwidths from the visible through the infrared spectral regions. Scientists use Infrared (IR) data to make rough estimates of tropical precipitation. The VIRS, PR and TMI data will help improve the techniques by which scientists use IR data from other satellites to calculate rainfall. This is the third component of TRMM's rain package.

• The Lightning Imaging Sensor (LIS) is an optical telescope and filter imaging system that will investigate the distribution and variability of both atmospheric and cloud-to-ground lightning over the Earth. These instruments will contribute to our understanding of storm dynamics and will be correlated to levels of precipitation and the release of latent heat.

• The Clouds and the Earth's Radiant Energy System (CERES) is a visible/infrared sensor designed especially to measure energy rising from the surface of the Earth and the atmosphere including its constituents (e.g., clouds and aerosols). This energy, when balanced t the energy received by the Earth from the Sun, constitutes the Earth's radiation budget. Understanding the radiation budget, from the top of the atmosphere to the Earth's surface, is important to understanding climate and its variability.

Science Data Retrieval and Transmission Process

TRMM has its own unique Science Data and Information System (TSDIS) at the GSFC to process the information from the satellite. TSDIS will analyze the rainfall data and also provide validation from nearly a dozen ground radar sites. The data products will be available to the science community from the Goddard Distributed Active Archive Center (GDAAC) about 6 months after launch.

• TRMM data will be provided on five levels, on a scale of zero to four, representing the different processing done at each stage after GSFC receives the data. Level zero is the time ordered and quality checked raw data received from the satellite. The higher levels result from combining hardware and software calibrations with the data to form the final products.
• Through TSDIS, GSFC will provide preprocessing of rainfall data (PR, TMI, VIRS) and all ground data transmit it to appropriate centers and to the GDAAC archives.
• The data also will be transmitted to Japan, where higher level processing will be performed at NASDA's Earth Observation Center (EOC). It will then be distributed to scientists in the fields of climatology, meteorology, hydrology and other disciplines in Japan and the United States.

Privacy, Security, Notices

Return to TSDIS Homepage