An Extension of the Column Model Technique for Estimating Outgoing Longwave Irradiance: The Column Weighting Model

Abstract

The procedure used by NOAA to estimate the outgoing longwave irradiance at the top of the atmosphere from an array of satellite window region measurements includes the averaging of the flux values inferred from the columns encompassing the satellite scan spots. The flux associated with a particular averaging region of interest is assumed to have contributions from only those points contained within the region. However, the area immediately surrounding a particular averaging region contributes to the flux estimate associated with that large averaging area. A new technique, based on the geometrical description of the flux associated with a single scan spot, is presented to estimate the uncertainty of the current averaging technique and to provide an alternative method for performing the averaging. Comparisons between the operational technique and the new technique show flux differences as large as 7% in the presence of high clouds when there are differences of 60% or more in cloud amounts between the averaging region and the area immediately surrounding it.