Sub-Footprint Spatial Inhomogeneity Effect on Geostationary Hyperspectral Infrared Sounder Radiance Simulation

Hyperspectral infrared (IR) sounders onboard the geostationary satellites have revolutionized our understanding of Earth's atmosphere by providing detailed measurements of temperature, moisture, and trace gases with high temporal resolution. However, the accuracy of these measurements and corresponding simulations can be affected by the sub-footprint atmospheric spatial variations. In this study, we investigated the impact of sub-footprint atmospheric spatial inhomogeneity (SASI) effects on geostationary hyperspectral IR sounder (GeoHIS) radiance simulations with very high spatial resolution atmospheric profiles across different spectral channels and viewing geometries under clear-sky conditions. Results reveal significant deviations greater than 1.0 K between simulated radiances considering SASI effects and those assuming a plane-parallel atmosphere, especially for weak absorption and window channels. These deviations exhibit strong spectral and view angle dependencies, emphasizing the importance of accounting for SASI effects in representativeness error estimation, instrument inter-comparisons, sounding retrievals and data assimilation in numerical weather prediction using GeoHIS radiances.