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.

Freshwater seems abundant, but when accounting for all the water on Earth, it's in limited supply. Just three percent of the water on our planet is freshwater. A majority of this water, about two percent of the world total, is contained in glaciers and ice sheets or stored below ground. The remaining one percent is found in lakes, rivers and wetland areas or transported through the atmosphere in the form of water vapor, clouds and precipitation. Rain and snowfall replenish freshwater sources, making it vital to know when, where and how much water is falling at any given time. Using NASA's Global Precipitation Measurement satellite, researchers can track precipitation worldwide and monitor levels from space.

For more information on Earth's water resources, visit: http://water.usgs.gov/edu/earthwherewater.html