GEO/SAMS-the Geostationary Synthetic Aperture Microwave Sounder

NOAA has for many years operated two weather satellite systems, the Polar-orbiting Operational Environmental Satellite system (POES), using low-earth orbiting (LEO) satellites, and GOES, using geostationary Earth orbiting (GEO) satellites. The POES satellites have been equipped with both infrared (IR) and microwave (MW) atmospheric sounders, which makes it possible to determine the vertical distribution of temperature and humidity in the troposphere even under cloudy conditions. Such satellite observations have had a significant impact on weather forecasting accuracy, especially in regions where in situ observations are sparse. In contrast, the GOES satellites have only been equipped with IR sounders, since it has not been feasible to build a large enough antenna to achieve sufficient spatial resolution for a MW sounder in GEO. As a result, GOES soundings can only be obtained in cloud free areas and in the less important upper atmosphere, above the cloud tops. This has hindered the effective use of GOES data in numerical weather prediction. Full sounding capabilities with the GOES system is highly desirable because of the advantageous spatial and temporal coverage that is possible from GEO. While POES satellites provide coverage in relatively narrow swaths, and with a revisit time of 12-24 hours or more, GOES satellites can provide continuous hemispheric coverage, making it possible to monitor highly dynamic phenomena such as hurricanes. In response to a NASA Research Announcement calling for innovative measurement concepts suitable for non-LEO deployment, GEO/SAMS was proposed as a solution to the GOES microwave sounder problem. Using an approach similar to the SMOS mission, GEO/SAMS synthesizes a large aperture to measure atmospheric parameters at high MW frequencies with high spatial resolution from GEO. In 1999 NASA's Office of Earth Science selected GEO/SAMS for a Phase A study, sponsored through the New Millennium Program.