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PRECIPITATION MEASUREMENT MISSIONS

Global Precipitation Measurement (GPM) Mission Overview

GPM: Global Precipitation Measurement Banner. 5 vertical panels depicting an approaching storm, TRMM 3D cloud measurements, the GPM core observatory, a tree with snowfall, and a hurricane as seen from space.

GPM Mission Concept

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.

Diagram of the various satellites which comprise the GPM Constellation

Building upon TRMM’s Legacy

The Tropical Rainfall Measuring Mission (TRMM), launched by NASA and JAXA in 1997, uses both active and passive microwave instruments to measure rainfall in the tropics. It also provides a foundation for merging rainfall information from other satellites. TRMM has shown the importance of taking observations from a non-Sun-synchronous orbit at different times of the day, between observations by polar orbiting sensors at fixed times of the day, to improve near real-time monitoring of hurricanes and accurate estimation of time-accumulation of rain volume. The GPM Core Observatory continues this  sampling from a non-Sun-synchronous orbit and extends coverage to higher latitudes to provide a global view of precipitation.

The GPM Core Observatory design is an extension of TRMM’s highly successful rain-sensing package, which focused primarily on heavy to moderate rain over tropical and subtropical oceans. Since light rain and falling snow account for significant fractions of precipitation occurrences in middle and high latitudes, a key advancement of GPM over TRMM is the extended capability to measure light rain (< 0.5 mm hr-1), solid precipitation and the microphysical properties of precipitating particles. This capability drives the designs of both the active and passive microwave instruments on GPM. The Core Observatory will then act as a reference standard for the precipitation estimates acquired by the GPM constellation of sensors.

GPM Core Observatory

The GPM Core Observatory carries the first space-borne Ku/Ka-band Dual-frequency Precipitation Radar (DPR) and a multi-channel GPM Microwave Imager (GMI). The DPR instrument, which provides three dimensional measurements of precipitation structure over 78 and 152 mile (125 and 245 km) swaths, consists of a Ka-band precipitation radar (KaPR) operating at 35.5 GHz and a Ku-band precipitation radar (KuPR) operating at 13.6 GHz. Relative to the TRMM precipitation radar, the DPR is more sensitive to light rain rates and snowfall. In addition, simultaneous measurements by the overlapping of Ka/Ku-bands of the DPR can provide new information on particle drop size distributions over moderate precipitation intensities. In addition, by providing new microphysical measurements from the DPR to complement cloud and aerosol observations, GPM is expected to provide further insights into how precipitation processes may be affected by human activities.

The GMI instrument is a conical-scanning multi-channel microwave radiometer covering a swath of 550 miles (885 km) with thirteen channels ranging in frequency from 10 GHz to 183 GHz. The GMI uses a set of frequencies that have been optimized over the past two decades to retrieve heavy, moderate and light precipitation using the polarization difference at each channel as an indicator of the optical thickness and water content.

Swath covered by GPM sensors.
Swath covered by GPM sensors

GPM Science and Applications

GPM will provide global precipitation measurements with improved accuracy, coverage and dynamic range for studying precipitation characteristics. GPM is also expected to improve weather and precipitation forecasts through assimilation of instantaneous precipitation information. Relative to TRMM, the enhanced measurement and sampling capabilities of GPM will offer many advanced science contributions and societal benefits:

Learn more about GPM's science objectives.

Learn more about GPM's applications.

 

MISSION UPDATES

  • The Precipitation Processing System (PPS) has begun producing updated GPM radiometer products as of 12/4/2014 due to an error discovered in the calculation of the Sun Angle in the PPS Geolocation Toolkit. This is considered a minor update with the...
  • The TRMM satellite is descending, and the users of TRMM Precipitation Radar (PR) data should be aware that the last production orbit of public PR data was orbit #96230 from October 7th, 2014. From that point forward, the TRMM PR data is suspended because...
  • The most accurate and comprehensive collection of rain, snowfall and other types of precipitation data ever assembled now is available to the public. This new resource for climate studies, weather forecasting, and other applications is based on...
  • Since December 1997, TRMM and the instruments it carries have provided valuable information to researchers, the applications community, and the public. On July 8, 2014, pressure readings from the fuel tank indicated that TRMM is at the end of its fuel....