Case Studies for the Investigation of Cloud Sensitive Parameters as Measured by GOME

This project focuses on the determination of cloud properties (like geometric cloud fraction and average cloud to height) from satellite observations and on the quantification of the corresponding cloud influence on tropospheric trace gas products derived from satellites (see e.g.Burrows et al. 2000; Richter et al. 2002; Wagner et al. 2002a). The investigations first concentrate on GOME and will later also be applied to SCIAMACHY on ENVISAT.The most dominant effects of clouds are (a) that they shield the atmosphere below the cloud cover, and (b) that their albedo is typically significantly larger compared to the earth’s surface. Because of these effects the determination of quantitative tropospheric trace gas products depends strongly on the knowledge of cloud properties.Cloud algorithms which already exist are based on spatially resolved intensity measurements (Polarisation measurement devices, PMD, see ESA (1995)) as well as on the determination of the optical depth of the OrA band (see e.g. (1994), Kjoelemeijer and Stammes 1999). However, both quantities show important shortcomings, especially over snow and ice surfaces, which strongly limit their applicability.In this study we investigate a large variety of cloud sensitive parameters measured by GaME. Besides the “traditional” cloud sensitive parameters mentioned above we also investigate the polarisation of the measured light and in particular of various absorption bands of the oxygen dimer O₄ (at 360, 380, 477, 577 and 630 nm (Greenblatt et al. 1990)) as well as the filling-in of the solar Fraunhofer lines by inelastic Raman scattering. We demonstrate that several of these quantities are well suited for the characterisation of clouds, especially over snow and ice surfaces.