Accelerated Line-by-Line Calculation of Spectral Absorption Coefficients with High Numerical Accuracy

Abstract

To model radiative transfer through the atmosphere with high accuracy, one must resort to the calculation of spectral absorption coefficients on a line by-line basis. The calculation of these coefficients is computationally expensive for three reasons: (1) thousands of spectral lines can contribute to absorption at a single frequency: (2) the tails of spectral line profiles are long (i.e., a given line can contribute to absorption over a wide range of frequencies), and (3) the sampling frequencies at which monochromatic radiances are to be calculated must be spaced sufficiently close together to resolve the thinnest lines of interest (e.g., those that arise in the stratosphere). We have developed a new algorithm to accelerate the calculation of spectral absorption coefficients while retaining high numerical accuracy.