Efficient line-by-line technique for calculating accurate and compact spectral lookup tables for satellite remote sensing

Abstract

ABSTRACT This paper presents an efficient line-by-line (LBL) technique for the fast computation of compact and precise spectral lookup tables (LUTs) for LBL radiative transfer models. The key feature of this technique is obtaining and using efficient non-uniform wavenumber grids for line profile interpolations with a given accuracy. Grid points are concentrated at the centre of the lines and are rare in the wings. In case of narrow and isolated spectral lines, this technique derives LUTs that are compact by several orders of magnitude than those that use uniform grids. The potential of this technique is demonstrated using the problem of calculating non-Voigt line profiles, as suggested by Hartmann and Tran (HTP). The size of LUTs for the replacement of direct calculations of HTPs in forward remote sensing models is estimated, and a set of LUTs for H2O lines are created and written as ASCII files in http://wadis.saga.iao.ru/view/hartmann-tran/. Furthermore, the conditions under which this technique can speed up (by approximately one order of magnitude) forward LBL models are discussed.