In the presence of broken clouds over snow or ice covered surfaces it is difficult for UV/VIS spaceborne sensors to distinguish between clouds and high reflecting surfaces. These uncertainties lead to problems in the ozone retrieval. A new approach presented here characterizes the inhomogeneous pixel area (with broken clouds) by deriving an effective albedo and cloud-top-height. These parameters are determined by minimizing the difference between GOME measured sun-normalized radiances and corresponding model spectra in the spectral range of O<SUB>4</SUB> absorption near 370 nm. Extrapolation of this effective albedo to short wavelengths enables to improve the ozone retrieval. Besides this new retrieval method some new calibration corrections are made for the GOME spectra which take into account instrumental effects from dark current or straylight and the degradation from GOME.