A new algorithmic approach to retrieve total ozone from nadir observations of
the Global Ozone Monitoring Experiment has been developed. By fitting the
vertically integrated ozone weighting function rather than ozone cross-section
to the sun-normalised radiances, a direct retrieval of vertical column amounts
are possible. This new weighting function DOAS approach takes into account the
slant path wavelength modulation that is usually neglected in the standard DOAS
approach using single airmass factors. Further improvements have been achieved
by taking into account molecular (ozone) filling-in as part of the so-called
Ring effect. The validation results from comparison with ground based
measurements from Dobson and Brewer instruments show significant improvement
over the current GOME Version 3.0. This makes the new algorithm attractive for
application to SCIAMACHY and future satellite instruments like OMI and GOME2.