Intercomparison of EGA, CGA, and LBL forward model computation schemes for SAGE III water vapor retrieval

摘要

This paper presents a comparison of the three forward model computational schemes, namely, Emissivity Growth Approximation (EGA), Curtis-Godson Approximation (CGA), and line-by-line (LBL) approach developed for SAGE III water vapor retrieval. For all three schemes, we have incorporated the most recent laboratory measurements of spectral line parameters to avoid the bias which is known to exist in HITRAN-96 database. Discussions are focused on the strength and weakness of each scheme with respect to accuracy and computational efficiency. The computer time for the LBL has been reduced significantly. The advantage of the LBL is manifest when the dependence of EGA and CGA on a huge pre-calculated lookup table and the breakdown of assumptions for these two schemes at lower altitudes are taken into account.