The TRMM and GPM Missions

[no-glossary]Global Precipitation Measurement[/no-glossary]

The Global Precipitation Measurement (GPM) mission is a partnership co-led by NASA and the Japan Aerospace Exploration Agency (JAXA). The mission centers on the deployment of the GPM Core Observatory and consists of an international network, or constellation, of eight additional satellites that together will provide next-generation global observations of precipitation from space. The GPM Core satellite will carry an advanced radar/radiometer system and serve as a reference standard to unify precipitation measurements from all satellites that fly within the constellation. 

Visualization of the GPM Core Observatory orbiting Earth, with constellation satellites in the background. Visualization of the GPM Core Observatory orbiting Earth, with constellation satellites in the background.
The GPM Core Observatory will carry two instruments: the GPM Microwave Imager (GMI) and Dual-frequency Precipitation Radar (DPR). These instruments will return improved observations that will allow scientists to “see” inside clouds. The GMI has the capability to measure the amount, size, intensity and type of precipitation, from heavy-to-moderate rain to near-imperceptible light rain and snow. The DPR will return three-dimensional profiles and intensities of liquid and solid precipitation. These data will reveal the internal structure of storms within and below clouds. 
The GPM mission concept builds on the success of the Tropical Rainfall Measuring Mission (TRMM), a joint NASA and JAXA satellite launched in 1997 that measures precipitation over tropical and subtropical regions, from the Mediterranean Sea (35° north latitude) to the southern tip of South Africa (35° south latitude). 
Measurements from the GPM Core, however, will provide even greater coverage—between the Arctic Circle (65° north latitude) and the Antarctic Circle (65° south latitude). These measurements, combined with those from other polar-orbiting satellites in the constellation, will provide global precipitation datasets every three hours. This integrated approach and unified dataset will help advance scientists' understanding of Earth's water and energy cycle. 
The GPM constellation will provide measurements on the: 
  • intensity and variability of precipitation;
  • three-dimensional structure of cloud and storm systems; 
  • microphysics of the ice and liquid particles within clouds; and
  • amount of water falling to Earth’s surface. 
Observations from the GPM constellation, combined with land-surface data, will improve:
  • weather forecasts;
  • forecasts of hurricanes, floods and droughts;
  • integrated hydrologic models of watersheds; and
  • climate models.
Above all, global observations from GPM mission satellites will continue and expand the data records that began with previous precipitation missions, such as TRMM, and improve precipitation estimates around the globe. The mission will help scientists understand how local, regional and global precipitation patterns change over time. 

Tropical Rainfall Measuring Mission

NASA's Tropical Rainfall Measuring Mission (TRMM) was launched on Nov. 27, 1997, and for the last fifteen years has enabled precipitation science that has had far reaching applications across the globe.

Visualization of the TRMM satellite. Visualization of the TRMM satellite.
Nowhere on Earth does it rain more than across the tropics. Orbiting at an angle to the equator that covers 35 degrees north to 35 degrees south of the equator, TRMM carries five instruments that collectively measure the intensity of rainfall, characteristics of the water vapor and clouds, and lightning associated with the rain events. One of the instruments, the Precipitation Radar, built by JAXA, was the first precipitation radar flown in space. It still returns images of storms that reveal close up, three-dimensional views of how rainbands in tropical cyclones develop, potentially indicating how strong the storms might become.
Originally a three-year mission, TRMM's mission life was extended because its data added a huge value to forecasts of tropical cyclones. In addition, its fifteen-year record of rainfall has provided a great boon to the scientific understanding of precipitation and its role in broad weather patterns and climate. TRMM has given scientists data that allows them a better understanding of how rain varies daily, seasonally, and annually; how El Nino affects global rain patterns; how regional rain events like the Indian monsoon vary throughout the season; and even how humans have impacted local precipitation through the effects of urban heat islands, deforestation, and pollution.
While TRMM continues to collect valuable science data, its fuel will eventually run out for operations. GPM will continue and expand on TRMM's measurement. It is gearing up for launch in February 2014.