Estimation of outgoing longwave radiation from Atmospheric Infrared Sounder radiance measurements

This study demonstrates the ability to use Atmospheric Infrared Sounder (AIRS) hyperspectral radiance measurements and collocated Clouds and the Earth's Radiant Energy System outgoing longwave fluxes to estimate top‐of‐atmosphere outgoing longwave radiation (OLR) from AIRS radiance measurements. The first 35 principal component scores of AIRS radiances from its 1707 pristine channels are used as predictors, and the regression coefficients are generated in eight regimes of AIRS view angle to account for angular dependence of the AIRS radiance observations. Tests on an independence test ensemble show that the accuracy of the AIRS OLR is near zero and the precision is less than 3 Wm−2 for all scenes and 2 Wm−2 for uniform scenes. The AIRS OLR precision for uniform scenes is much higher than the High‐Resolution Infrared Sounder OLR of 5 Wm−2 for similar comparisons with the Earth Radiation Budget Experiment OLR. The same technique of empirical regression OLR can be applied to other hyperspectral sounders such as the Cross‐track Infrared Sounder that will be on board the National Polar‐Orbiting Operational Environmental Satellite System and the Infrared Atmospheric Sounding Interferometer on the European Meteorological Polar‐orbiting satellites.