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 ultimately improve operation 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 Imaging Spectrometer uses spatially variable wedge filter spectrometers to collect earth radiance with approximately 2 km resolution over a 710-2900 cm-1 spectral range at 1 percent spectral resolution. The resulting instrument, based on LWIR and MWIR wedge-filter spectrometer technology recently developed by Raytheon, would be a compact, rugged imager-sounder with better sensitivity, spectral resolution, spatial resolution and full disk coverage time than current multispectral operational GEO imagers. Sounding performance was simulated with respect to a global database of 119,694 cloud-free samples using a stepwise regression algorithm. Retrieved atmospheric parameters included surface air temperature, surface skin temperature, surface water vapor, total precipitable water vapor, total ozone and vertical profiles of temperature and water vapor. Not only did the conceptual WIS-based instrument outperform the current operation GEO sounder, but also RMS error performance approached that of advance higher spectral resolution sounders. Due to its higher spatial resolution and more compete spatial coverage, WIS could achieve this high quality cloud free sounding performance roughly two times more frequently than high spectral resolution advance sounders. Combining this new technology with proven wedge spectrometer approaches for visible and near-IR wavelengths would provide imaging-sounding data from GEO with unprecedented detail and fidelity for a wide range of weather, climate, land use, ocean color and other earth science studies.