Assessment of the Single-Mixture Gas Assumption for the Correlated $K$-Distribution Fictitious Gas Method in $H2O–CO2–CO$ Mixture at High Temperature

This paper deals with the comparison of spectral narrow band models based on the correlated-$K$ (CK) approach in the specific area of remote sensing of plume signatures. The CK models chosen may or may not include the fictitious gas (FG) idea and the single-mixture-gas assumption (SMG). The accuracy of the CK and the CK-SMG as well as the CKFG and CKFG-SMG models are compared, and the influence of the SMG assumption is inferred. The errors induced by each model are compared in a sensitivity study involving the plume thickness and the atmospheric path length as parameters. This study is conducted in two remote-sensing situations with different absolute pressures at sea level $(105Pa)$ and at high altitude (⁠$16.6km$⁠, $104Pa$⁠). The comparisons are done on the basis of the error obtained for the integrated intensity while leaving a line of sight that is computed in three common spectral bands: $2000–2500cm−1$⁠, $3450–3850cm−1$⁠, and $3850–4150cm−1$⁠. In most situations, the SMG assumption induces negligible differences. Furthermore, compared to the CKFG model, the CKFG-SMG model results in a reduction of the computational time by a factor of 2.