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Earth Science and Applications from Space 21 PATH Precipitation and All-Weather Temperature and Humidity Launch: 2016â2020 Mission size: Medium Orbit: GEO Agency: NASA Estimated cost: $450 million Areas of interest: Health, Water, Weather Instrument: Microwave array spectrometer Benefits: More accurate weather forecasts and warnings Improved prediction of storm track and intensity and improved evacuation planning Improved forecasts of hurricane storm surge and rainfall accumulation Frequently updated temperature and moisture data are critical to high-quality forecasts of weather, particularly hurricanes, floods, and other high-impact events. For many years, satellites in low Earth orbit have routinely gathered pro- files of temperature, water vapor, and the amount of liquid water within clouds using microwave spectrometers and infrared sounders. Infrared sounders can be used in geostationary orbit to enable more frequent regional observations, although their performance is limited by clouds and precipitation. Limits on microwave technology have thus far kept these spectrometers from accessing the vantage point of geostationary orbit to enable more frequent regional observations under all weather conditions. PATH will provide the first geostationary platform for a microwave spectrometer and infrared sounder in tandem. The mission will analyze temperature and water vapor in three dimensions, as well as sea surface temperature and precipitation. Data will be gathered every 15 to 30 minutes in both clear and cloudy conditions. PATH will lead to more accurate weather forecasts through greatly improved models of the atmosphereâs lowest kilometer and the processes that shape clouds, rainfall, and snowfall. The fre- quently updated observations of wind speed and sea surface temperature will increase the accuracy of hurricane track, intensity, and storm surge forecasts. Water vapor and rain- fall data will enhance flood prediction. A geostationary orbit will allow PATH to carry out samp- ling that would otherwise require an impractically large constellation of satellites. A platform in mid-Earth orbit is another possibility; however, additional instrument development would be needed for this option.