An improvement in fast radiative transfer calculation of FengYun satellite by Planck weighting correction

Abstract

A unified regression method to calculate fast transmittance coefficients is used in fast radiative transfer calculation of satellite infrared channel by a convoluted transmittances database from LBL (Line_By_Line) model. Comparison is performed between the fast calculated brightness temperature and LBL calculations for VISSR/FY-2F and IRAS/FY-3B. The examination indicates that STD (Standard Deviation) of fast calculated brightness temperature in window channels are much larger than the values in sounding channels. The lower atmosphere the channel detects, the larger the STD is available. And the largest the STD is less than 0.4 K. In this paper, a discussion is given to the improvement of fast radiative transfer calculation brought about by Planck weighted correction for convoluted channels' transmittances. Analysis shows that overlap between 2350 cm-1 and spectral response filter of the channel is a requirement to the Planck weighted correction. It is shown that STDs of brightness temperature between LBL calculation and fast computation are decreased by 25% after Planck weighted correction. And the improvement is available only for such channels with an overlap between their filter function and 2350 cm-1. Also it is indicated that the improvement from Planck weighted correction could be used not only to the imaging channels that have wide spectral coverage, but also to the sounding channels with very narrow spectral fields.