An improved WSGGM-based narrow band model for the CO 2 4.3 μm band

Abstract

An accurate WSGGM-based narrow band (WNB) model is investigated in the CO 2 4.3 μm band for use in inverse radiative instrumentation. The WNB model of Kim and Song is tested first with 24 gray gases for all of the narrow bands and it shows significant error compared with the line-by-line (LBL) results for two typical non-isothermal layers. A modification of this model is proposed using the concept of correlated-distribution (CK) and assuming that the scaling approximation may be justified. With only seven gray gases taken independently for each narrow band (optimised and tabulated), this model shows less than 1% deviation from the LBL results for most of the important narrow bands around 4.3 μm. Further extension of the WNB model is tried by applying the CK fictitious gases (CKFG) concept by taking, independently for each narrow band, three fictitious gases for each of which three gray gases are taken. This results in 3 3 gray gases which are spectrally overlapped with each other in a random fashion. Despite the complexity and labour, the test of the CKFG-based WNB model reveals greater error (a few percent or more) than the previous CK-based modification for the CO 2 4.3 μm band. Therefore, use of the CK-based WNB model for accurate and economical computations is recommended.