What If We Had a Geostationary Microwave Sounder?

Sponsored by the NASA Earth Science Technology Offices (ESTO) Instrument Incubator Program (IIP), a feasible and realizable design and all required technology for a geostationary microwave sounder have been developed at the Jet Propulsion Laboratory. The Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) is essentially an AMSU in GEO and will provide similar measurements as are now obtained with the current low-earth-orbiting microwave sounders, AMSU and ATMS, but every 15 minutes or less instead of every 12 hours and covering a large portion of a hemisphere instead of a narrow swath. GEO orbits are almost 50 times higher than the LEO orbits that current microwave sounders operate from, and the corresponding scaling of aperture size required to maintain spatial resolution had stymied the development of such a sensor for many decades in spite of an expectation in the atmospheric science community that a geostationary microwave sounder would revolutionize the field. The aperture synthesis approach implemented with GeoSTAR finally overcomes that obstacle, and the large number of microwave receivers and associated electronics required is made possible with the new technology that has now been developed and fully tested and is ready for implementation. During the latter half of 2020 a detailed study of GeoSTAR and its projected performance was undertaken. The study determined that the performance of such a system will match, and in some areas exceed, the performance of AMSU and ATMS and will lead to significant improvements in both regional and global weather prediction, particularly for tropical cyclones. It will also provide vertical profiles of atmospheric wind vectors under almost any weather condition. We present a summary of our findings, including instrument characteristics, measurement accuracy and precision, and expected impact on atmospheric research, weather prediction, and applications. Copyright 2021 California Institute of Technology