Sounding Performance of a Wedge-filter Imager-Sounder in Geostationary Orbit

Imaging spectrometry from geostationary earth orbit (GEO) can provide the frequently-refreshed detailed information on physical properties of earth's atmosphere and surface needed to enable critical new science missions and improve operational weather forecasting. We describe and evaluate a concept for imaging spectrometry from GEO that addresses both traditional imaging and sounding applications. Our Geostationary Wedge-filter Imager-Sounder (GWIS) uses a spatially variable wedge filter spectrometer to collect earth radiance with ~2 km resolution over a 710-2900 cm-1 (3.45-14.0 µm) spectral range at 1% spectral resolution. This technology offers a simple, efficient and low cost approach for applications that may not require high spectral resolution, but benefit from high spatial resolution such as detailed cloud properties mapping and wind profiling. We evaluated performance of this conceptual instrument for sounding of atmospheric parameters including vertical temperature and water vapor profiles. We find that GWIS sounding performance is very close to that of advanced FTS and grating spectrometer sounders in terms of RMS error. For instance, for cloud-free soundings, GWIS provides RMS accuracy of 1.2 K in 1 km layers in the lower atmosphere versus 1 K in 1 km layers for advanced sounders. But, because GWIS provides spectral radiance data with 2 km spatial resolution versus 8-16 km for advanced sounders, the probability of GWIS providing a cloud-free sounding within a 50 km by 50 km region is >95% versus ~50% for advanced sounders.