Understanding the Earth's climate and how it responds to climate perturbations relies on knowledge of how
atmospheric moisture, clouds, latent heating, and the large-scale circulation vary with changing climate
conditions. The physical process that links these key climate elements is precipitation. The Global
Precipitation Measurement (GPM) mission will be key to answering the following related research
•how are global precipitation, evaporation, and the cycling of water changing?
•how are variations in local weather, precipitation, and water resources related to global climate
•how can weather forecast duration and reliability be improved by new space-based observations,
data assimilation and modeling?
GPM is a joint initiative with the Japan Aerospace Exploration Agency (JAXA) and other international
partners that integrates previously planned and dedicated missions in a scalable and evolving constellation
of multiple spacecraft and data processing and validation ground systems. Its science objectives are:
•to improve ongoing efforts to predict climate by providing near-global measurement of
precipitation, its distribution, and physical processes;
•to improve the accuracy of weather and precipitation forecasts through more accurate
measurement of rain rates and latent heating;
•to provide more frequent and complete sampling of the Earth's precipitation.
It is a potential component of the Global Earth Observation System of Systems (GEOSS) as envisioned by
the intergovernmental Group on Earth Observations (GEO). GPM will consist of a core spacecraft to
measure precipitation structure and to provide a calibration standard for the constellation spacecraft, an
international constellation of NASA and contributed spacecraft to provide frequent precipitation
measurements on a global basis, calibration/validation sites distributed globally with a broad array of
precipitation-measuring instrumentation, and a global precipitation data system to produce and distribute
global rain maps and climate research products. GPM is now in formulation phase. GPM launches are
targeted to begin in 2013.