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Earth Science and Applications from Space 16 GPSRO Operational GPS Radio Occultation Launch: 2010â2013 Mission size: Small Orbit: LEO Agency: NOAA Estimated cost: $150 million Areas of interest: Climate, Health, Water, Weather Instruments: GPS receivers Benefits: Benchmarking of climate observations for establishing trends and variability in climate More accurate, longer-term weather forecasts Improved forecasts of space weather Forecasts of weather at ground level as well as prediction of âspace weatherââthe impacts of solar storms and other high-altitude distur- bancesâare limited by inadequate three-dimensional data, especially over the oceans and other hard-to-sample areas. This not only hinders the accuracy of weather forecast models but also complicates the effort to monitor long-term changes in global climate. At higher altitudes, a lack of data adds to the challenge of predicting space-weather impacts that can range from communications blackouts to power grid disruptions. GPSRO will benefit forecasts of weather, climate, and space weather by employing approximately six satellites in low Earth orbit, each intercepting signals from GPS satellites. By measuring the delays induced in these signals as they pass through the atmosphere, GPSRO will produce precise, accurate soundings of atmospheric refractivity at high vertical resolution. In turn, these profiles can yield three-dimensional information on electron density in the ionosphere, temperature in the stratosphere and upper troposphere, and temperature and water vapor in the lower troposphere. These data will improve the analyses that feed into weather forecasts on scales of hours to many days, while also serving as an ideal benchmark for climate monitoring. The data on electron den- sity will enhance the quality of space-weather forecasts. The techniques in GPSRO have been tested and verified through several successful proof-of-concept missions involving single satellites and through the six-satellite Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), launched in 2006. The committee recommends that GPSRO be launched near the end of the COSMIC mission, around 2012.