Stuck in the Valley of Death: GeoSTAR, NASA’s Geostationary Microwave Sounder

A geostationary microwave sounder, capable of providing continuous monitoring the atmosphere 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 at the Jet Propulsion Laboratory. The Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) provides measurements similar to those now obtained with low-earth-orbiting microwave sounders but continuously instead of every 12 hours and covering an entire hemisphere instead of a narrow scan swath, thus enabling life cycle observations of very fast evolving phenomena, such as severe storms, that are often obscured from other sensors by heavy cloud cover. The continuous observations also make it possible to derive atmospheric wind vectors throughout the troposphere, and a reconfigurable spectrometer makes it possible to implement channel sets that are optimized for focused observations of specific regions of the atmosphere, such as the planetary boundary layer. Such an observing system has been near the top of the wish list of both the research and operational communities for many years. GEO orbits are almost 50 times higher than the LEO orbits that current microwave sounders operate from, and the very large aperture size required to achieve adequate 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, made possible with new technology that has now been developed and fully tested. Mission development can start as soon as funding is available.

This was the situation in 2016, when the development culminated with clear evidence that it could fulfill important NASA research objectives, and was the situation in 2021, after a feasibility study for NOAA was completed that showed that it could form an element NOAA’s GEO-XO constellation. Neither organization has found a way to implement a space mission, and GeoSTAR is thus in limbo in the R2O “valley of death”.

We will review the GeoSTAR design and technology and discuss some of the exciting research and applications that it enables, which range from real-time hurricane monitoring to high-resolution soundings of the planetary boundary layer.

Copyright 2024 California Institute of Technology. Government sponsorship acknowledged.