Impact of Spectroscopic Line Parameters on Carbon Monoxide Column Density Retrievals from Shortwave Infrared Nadir Observations

Abstract

Among the various input data required for retrieval of atmospheric state parameters from infrared remote sensing observations molecular spectroscopy line data have a central role, because the data quality is critical for the quality of the retrieval product. Here we discuss the impact of the line parameters on vertical column densities (VCD) estimated from short wave infrared nadir observations. Using BIRRA (the Beer InfraRed Retrieval Algorithm) comprising a line-by-line radiative transfer code (forward model) and a separable nonlinear least squares solver for inversion we retrieve carbon monoxide from observations of SCIAMACHY aboard Envisat. Retrievals using the two recent versions of HITRAN (2008 and 2012) and GEISA 2011 have been performed and the results are compared in terms of residual norms, molecular density scaling factors, their corresponding errors, and the final VCD product. The retrievals turn out to be quite similar for all three databases, so a definite recommendation in favor of one of these databases is difficult for the considered spectral range around 2.3mue. Nevertheless, HITRAN 2012 appears to be advantageous when evaluating the different quality criteria.