Sensitivity Analysis for SCIAMACHY Ozone Limb Retrieval

Abstract

Limb measurements performed by the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) on the ENVISAT satellite enable a retrieval of stratospheric profiles for various trace gases on a global scale. The operational SCIAMACHY L1b-2 processor was developed on behalf of ESA at German Aerospace Center (DLR). The more sophisticated, so called “scientific”, version of the operational processor without any operational constraints is developed parallel and give us free hand for all sorts of experiments. In this paper we analyze different inversion models suitable for the ozone retrieval from SCIAMACHY limb measurement data. This analysis is performed by means of the scientific processor. The inversion algorithms comprise differential and absolute radiance models with multiple spectral windows as well as the radiance model together with Chappuis triplets. The sensitivity of the retrieval algorithm in dependance on the chosen inversion model is investigated and discussed. Since till now the operational ozone limb retrieval was performed up to 45 km only, special attention is given to the upper stratosphere (45 - 65 km). A large class of regularization methods as for instance, the Tikhonov regularization, the iteratively regularized Gauss-Newton method, the regularizing Levenberg-Marquardt method, the asymptotical regularization approach and the regularized total least-squares method can be used in the scientific processor. Their efficiency is tested and test results are presented in the paper. The impact of a Picard iteration model for simulating the radiating transfer in a two-dimensional spherical shell atmosphere is also discussed.