Planck Weighted Transmittance and Correction of Solar Reflection for Broadband Infrared Satellite Channels

摘要

Three approximations methods to calculate the level-tospacetransmittance, used in fast radiative transfer model,are studied for five infrared broadband channels. Two ofthem are Planck-weighted transmittances, in which oneinvolves the effective layer temperature of a layer (PW1),and the other involves temperatures at the interfacebetween layers (PW2). The third one is not includingtemperature at all (ORD). It is found that under allcircumstances method PW1 is better than method PW2compared to the line-by-line (LBL) calculation. Planckweightedmethods are more sensitive to atmosphericsurface temperatures compared to ORD method.Based on these simulations and comparisons, when theband correction is larger (greater than 1), PW1 methodshould be used to take account of the Planck radiancechanging with the transmittance within the band spectral.When considering the solar contribution in daytime,correction of the solar reflection has been made for nearinfrared broadband channels (～3.7 μm) when using PW1transmittance. The solar transmittance is predicted byusing explanatory variables as PW1 transmittance, secantof zenith angle, and surface temperature. With thecorrection, the error reduces to more reasonable level.