Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 4 4 2004 10.5194/acpd-4-4915-2004 http://www.atmos-chem-phys-discuss.net/4/4915/2004/ http://www.atmos-chem-phys-discuss.net/4/4915/2004/acpd-4-4915-2004.html http://www.atmos-chem-phys-discuss.net/4/4915/2004/acpd-4-4915-2004.pdf 4915 4944 2004-08-31 Total ozone retrieval from GOME UV spectral data using the weighting function DOAS approach M. Coldewey-Egbers coldewey@iup.physik.uni-bremen.de M. Weber L. N. Lamsal R. de Beek M. Buchwitz J. P. Burrows Institute of Environmental Physics, University of Bremen, Bremen, Germany A new algorithm approach called Weighting Function Differential Optical Absorption Spectroscopy (WFDOAS) is presented which has been developed to retrieve total ozone columns from nadir observations of the Global Ozone Monitoring Experiment. By fitting the vertically integrated ozone weighting function rather than ozone cross-section to the sun-normalized radiances, a direct retrieval of vertical column amounts is possible. The new WFDOAS approach takes into account the slant path wavelength modulation that is usually neglected in the standard DOAS approach using single airmass factors. This paper focuses on the algorithm description and error analysis, while in a companion paper by Weber et al. (2004) a detailed validation with groundbased measurements is presented. For the first time several auxiliary quantities directly derived from the GOME spectral range such as cloud-top-height and cloud fraction (O₂-A band) and effective albedo using the Lambertian Equivalent Reflectivity (LER) near 377 nm are used in combination as input to the ozone retrieval. In addition the varying ozone dependent contribution to the Raman correction in scattered light known as Ring effect has been included. Detailed investigations have been performed concerning the influence of the molecular ozone filling-in as part of the Ring effect. The precision of the total ozone retrieval is estimated to be better than 3% for solar zenith angles below 80°.