Deriving clear-sky longwave spectral flux from spaceborne hyperspectral radiance measurements: a case study with AIRS observations

• Main Authors: X. Chen, X. Huang
• Format: Article
• Language: English
• Published: Copernicus Publications 2016-12-01
• Series: Atmospheric Measurement Techniques
• Online Access: http://www.atmos-meas-tech.net/9/6013/2016/amt-9-6013-2016.pdf
• ISSN: 1867-1381; 1867-8548

Previous studies have shown that longwave (LW) spectral fluxes have unique merit in climate studies. Using Atmospheric Infrared Sounder (AIRS) radiances as a case study, this study presents an algorithm to derive the entire LW clear-sky spectral fluxes from spaceborne hyperspectral observations. No other auxiliary observations are needed in the algorithm. A clear-sky scene is identified using a three-step detection method. The identified clear-sky scenes are then categorized into different sub-scene types using information about precipitable water, lapse rate and surface temperature inferred from the AIRS radiances at six selected channels. A previously established algorithm is then used to invert AIRS radiances to spectral fluxes over the entire LW spectrum at 10 cm⁻¹ spectral interval. Accuracy of the algorithms is evaluated against collocated Clouds and the Earth's Radiant Energy System (CERES) observations. For nadir-view observations, the mean difference between outgoing longwave radiation (OLR) derived by this algorithm and the collocated CERES OLR is 1.52 Wm⁻² with a standard deviation of 2.46 Wm⁻². When the algorithm is extended for viewing zenith angle up to 45°, the performance is comparable to that for nadir-view results.