Py4CAtS - PYthon for Computational ATmospheric Spectroscopy

Abstract

Line-by-line models have become mandatory for many atmospheric spectroscopy applications. A large variety of models has been developed in the past, but in general these codes work as a kind of 'black box' where intermediate quantities such as cross sections are difficult to access. Py4CAtS --- PYthon scripts for Computational ATmospheric Spectroscopy is a Python re-implementation of our Fortran infrared radiative transfer code GARLIC (Generic Atmospheric Radiation Line-by-line Infrared Code), where compute-intensive code sections utilize the Numeric/Scientific Python modules for highly optimized array-processing. The individual steps of an infrared or microwave radiative transfer computation are implemented in separate scripts to extract lines of relevant molecules in the spectral range of interest, to compute line-by-line cross sections for given pressure(s) and temperature(s), to combine cross sections to absorption coefficients and optical depths, and to integrate along the line-of-sight to transmission and radiance/intensity. Py4CAtS can be used in two ways, from the Unix/Linux (or Windows/Mac) console/terminal or inside the (i)python interpreter. The basic design of the package, numerical and computational aspects relevant for optimization, and a sketch of the typical workflow are presented.