The development of a U.S. geostationary microwave sounder

A geostationary microwave sounder, capable of providing temperature, water vapor, clouds, precipitation, and wind vectors in the presence of clouds and precipitation, will add tremendously to our ability to observe dynamic atmospheric phenomena, such as hurricanes and severe storms, monsoonal moisture flow, atmospheric rivers, etc. Such a sensor is now feasible, enabled by technology that has been developed under NASA's Instrument Incubator Program. The Jet Propulsion Laboratory has led that development in partnership with the University of Michigan. A prototype, the Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR), is essentially an “AMSU in GEO”, i.e. it has similar capabilities as AMSU would have if it were operating on a geostationary satellite, including similar spatial resolution. GEO orbits are almost 50 times higher than the LEO orbits that current AMSUs operate from, and the corresponding scaling of aperture size required to maintain spatial resolution has stymied the development of such a sensor for many decades. 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. This development also enables the decadal-survey Precipitation and All-weather Temperature and Humidity (PATH) mission, and it is possible that NASA will elevate PATH from a low-priority “third-tier” mission to a higher priority first or second tier. In the meantime, a low-cost demonstration mission implementing a subset of the PATH objectives is feasible and has been proposed as a hosted payload on a commercial communications satellite, through the NASA EV-I Venture program. The objectives of such a mission is to advance our understanding and modeling of storm processes that control rapid or explosive intensification of hurricanes, mesoscale convective systems, and extratropical cyclones. Retrieval of temperature and water vapor profiles is possible even in the presence of moderate precipitation, and with the ability to derive horizontal wind vectors by tracking water vapor features, a rich set of parameters measuring the thermodynamics, dynamics and convection and sampled every 15 minutes, will enable significant progress in storm science.

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