About GPM and the Precipitation Processing System (PPS)

Please also visit the GPM and TRMM Homepage

 

Science Data Retrieval and Transmission Process

The Global Precipitation Measurement (GPM) mission has its own unique Precipitation Processing System (PPS), also formerly known as the TRMM Science Data and Information System (TSDIS) at the Goddard Space Flight Center (GSFC). The GPM mission includes the core GPM satellite (built at GSFC), data from the TRMM satellite (TRMM ceased operations in 2015), and the input data from our other GPM partner satellites. (PPS estimates liquid and solid precipitation using observations from an individual satellite sensor, multiple sensors, or multiple satellites. The data products are available to the science community and general public from our PPS 'HTTPS' and 'FTPS' archives once a simple registration process is completed. 

  • The PPS processes all the data returned by GPM constellation satellites, with the exception of data from the DPR. DPR data are sent to JAXA’s Mission Operations Systems for initial processing and returned to the PPS as a basic radar product for further processing and integration into global precipitation data products. GPM precipitation datasets will be freely available for download from the PPS website at https://arthurhou.pps.eosdis.nasa.gov/.
  • TRMM data was provided on five levels, on a scale of zero to three, 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 PPS, GSFC will provide preprocessing of rainfall data (PR, GMI, TMI, VIRS) and all ground data and transmit it to appropriate centers and to the GES-DISC archives.

  • The data also is transmitted to Japan, where higher level processing will be performed at JAXA'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 other countries.

    PPS Project Logo     Precipitation Processing System (PPS) Project Logo

Global Precipitation Measurement (GPM) Mission Overview:

The Global Precipitation Measurement (GPM) mission is an international network of satellites that provide the next-generation global observations of rain and snow. Building upon the success of the Tropical Rainfall Measuring Mission (TRMM), the GPM concept centers on the deployment of a “Core” satellite carrying an advanced radar / radiometer system to measure precipitation from space and serve as a reference standard to unify precipitation measurements from a constellation of research and operational satellites. Through improved measurements of precipitation globally, the GPM mission will help to advance our understanding of Earth's water and energy cycle, improve forecasting of extreme events that cause natural hazards and disasters, and extend current capabilities in using accurate and timely information of precipitation to directly benefit society.

GPM, initiated by NASA and the Japan Aerospace Exploration Agency (JAXA) as a global successor to TRMM, comprises a consortium of international space agencies, including the Centre National d’Études Spatiales (CNES), the Indian Space Research Organization (ISRO), the National Oceanic and Atmospheric Administration (NOAA), the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT), and others. The GPM Core Observatory launched on February 27th, 2014 at 1:37pm EST from Tanegashima Space Center, Japan.

Please See our Global Precipitation Measurement (GPM) mission Instruments Webpage for details on the GPM core satellite.

 

        GPM satellite in orbit and project logo

 

Tropical Rainfall Measuring Mission (TRMM) Overview:

Please Note that the TRMM Mission ceased operations in 2015. TRMM data is now integrated into the GPM constellation. The information below is for historical purposes.

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.

After extensive discussions and evaluation of impacts by TRMM Science Team members and spacecraft engineering support personnel, and after approvals by JAXA and NASA management, the decision was made to move the average operating altitude for TRMM between August 07, 2001 and August 24, 2001 from 350 kilometers to 402.5 kilometers. This will significantly extend the mission lifetime for TRMM. By use of a low-altitude orbit of approximately 250 miles (402.5 kilometers), TRMM's complement of state-of-the-art instruments provides more accurate measurements. These measurements increase our knowledge of how rainfall releases heat energy to drive atmospheric circulation.

TRMM's orbit ranges 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. Scientists can use data from this kind of orbit to calculate rain variations over a 24-hour period; the resultant data set is vastly more informative than any other available.

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

TRMM project logo   TRMM Project Logo

 

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.

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TRMM Observatory and Instruments

GSFC designed, built and tested the observatory "in house" at its Greenbelt, Maryland facility. At launch, the observatory weighed 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 provides 1,100 watts of load power to the satellite.

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

A reaction control subsystem maintains the orbit at approximately 250 miles (402 km). Data for each orbit is 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 follows:

TRMM satellite and Instruments

  • The Precipitation Radar (PR) determines 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 and 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 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 which investigates the distribution and variability of both atmospheric and cloud-to-ground lightning.  The data contributes 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 by 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.