In a data-processing room at NASA’s Goddard Space Flight Center in Greenbelt, Md., racks of high-powered computers are getting ready to make a map. It's not the familiar satellite map of farms, forests and cities. Instead, this map will show what's hovering above the ground — snowfall and rainfall. The data comes from the Global Precipitation Measurement mission, an international partnership led by NASA and the Japan Aerospace Exploration Agency. The GPM Core Observatory launched in early 2014, but the mission goes beyond data gathering data from one satellite. A constellation of spacecraft from U.S. agencies and other countries, all carrying similar instruments to measure rainfall, will contribute data to this global rain map. Compiling observations from these sources into one unified global data set is the job of the Precipitation Processing System at Goddard.