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Development of a Nonlinear Statistical Method for Estimating the Downward Longwave Radiation at the Surface from Satellite Observations

Abstract This paper develops a nonlinear statistical method that uses satellite radiance observations directly to estimate the downward longwave radiation (DLR) at the earth's surface, a necessary component of the surface energy budget. The proposed technique has rms regression errors of about 9 W m–2 for clear-sky conditions, and about 4 to 8 W m–2 for overcast conditions, depending on the cloud levels. It is shown that this technique can produce unbiased estimates over a large range of meteorological conditions, which is crucial for climate studies. Sensitivity studies show that the DLR is most sensitive to errors in the cloud amount on average. Overall, the combined errors for an instantaneous DLR estimate, excluding the effects of the surface pressure errors, range from about 7 to 12 W m–2 when there is a ±10% uncertainty in cloud amount and a ±100 hPa uncertainty in cloud-base pressure. When the cloud amount uncertainty rises to 30%, the combined DLR error ranges from about 10 to 25 W m–2. This clear...