The intent of GPM, currently planned for launch in the 2007-2008 time frame, is to address looming scientific questions arising in the context of global climate-water cycle interactions, weather prediction, hydro-meteorological prediction and prediction of freshwater resources. GPM is planning to expand the scope of precipitation measurement through the use of a constellation of 6-10 satellites, one of which will be an advanced TRMM-like "core" satellite carry dual-frequency Ku-Ka band radar and a microwave radiometer (e.g. TMI-like). The other constellation members will likely include new lightweight satellites and co-existing operational/research satellites carrying passive microwave radiometers. The goal behind the constellation is to achieve no worse than 3-hour sampling at any spot on the globe. The constellation's orbit architecture will consist of a mix of sun-synchronous and non-sun-synchronous satellites with the "core" satellite providing measurement of cloud-precipitation microphysical processes plus "training calibrating" information to be used with the retrieval algorithms for the constellation satellite measurements.
GPM is organized internationally, currently involving a partnership between NASA in the US and NASDA in Japan. However, the program is expected to involve additional international partners, other federal agencies, and a diverse collection of participants from academia, government, and the private sector. Additionally, the broad societal applications that will be enabled by GPM are reflected in NASA's selection of the mission as its signature representative to the United Nation's Peaceful Uses of Space program. Herein, an overview of the status and scientific agenda of GPM will be presented.