Nine U.S. and international satellites will soon be united by the Global Precipitation Measurement (GPM) mission, a partnership co-led by NASA and the Japan Aerospace Exploration Agency (JAXA). NASA and JAXA will provide the GPM Core satellite to serve as a reference for precipitation measurements made by this constellation of satellites, which will be combined into a single global dataset continually refreshed every three hours.
 
While each partner satellite has its own mission objective, they all carry a type of instrument called a radiometer that measures radiated energy from rainfall and snowfall. The GPM Core satellite carries two instruments: a state-of-the-art radiometer called the GPM Microwave Imager (GMI) and the first space-borne Dual-frequency Precipitation Radar (DPR), which sees the 3D structure of falling rain and snow. The DPR and GMI work in concert to provide a unique database that will be used to improve the accuracy and consistency of measurements from all partner satellites, which will then be combined into the uniform global precipitation dataset.
 
In this animation the orbit paths of the partner satellites of the GPM constellation fill in blue as the instruments pass over Earth. Rainfall appears light blue for light rain, yellow for moderate, and red for heavy rain. Partner satellites are traced in green and purple, and the GPM Core is traced in red.
 
The GPM Core observatory is currently being built and tested at NASA's Goddard Space Flight Center in Greenbelt, Md. It is scheduled to launch from Tanegashima space center in Japan in early 2014.