[1] The Global Ozone Monitoring Instrument (GOME) was launched on European Space Agency's ERS-2 platform in April 1995. The GOME data processor (GDP) operational retrieval algorithm has generated total ozone columns since July 1995. In 2004 the GDP system was given a major upgrade to version 4.0, a new validation was performed, and the 10-year GOME level 1 data record was reprocessed. In two papers, we describe the GDP 4.0 retrieval algorithm and present an error budget and sensitivity analysis (paper 1) and validation of the GDP total ozone product and the overall accuracy of the entire GOME ozone record (paper 2). GDP 4.0 uses an optimized differential optical absorption spectroscopy (DOAS) algorithm, with air mass factor (AMF) conversions calculated using the radiative transfer code linearized discrete ordinate radiative transfer (LIDORT). AMF computation is based on the TOMS version 8 ozone profile climatology, classified by total column, and AMFs are adjusted iteratively to reflect the DOAS slant column result. GDP 4.0 has improved wavelength calibration and reference spectra and includes a new molecular Ring correction to deal with distortion of ozone absorption features due to inelastic rotational Raman scattering effects. Preprocessing for cloud parameter estimation in GDP 4.0 is done using two new cloud correction algorithms: OCRA and ROCINN. For clear and cloudy scenes the precision of the ozone column product is better than 2.4 and 3.3%, respectively, for solar zenith angles up to 80°. Comparisons with ground-based data are generally at the 1-1.5% level or better for all regions outside the poles.Citation: Van Roozendael, M., et al. (2006), Ten years of GOME/ERS-2 total ozone data-The new GOME data processor (GDP) version 4: 1. Algorithm description,

[1] The atmospheric chemistry instrument Global Ozone Monitoring Experiment (GOME) was launched in April 1995 on the ERS-2 platform. The GOME data processor (GDP) operational retrieval algorithm has produced total ozone columns since July 1995. With a data record of over ten years, GOME has become important for ozone trend analysis. In 2004, GDP was upgraded to version 4.0, a new validation was performed, and the entire GOME data record was reprocessed. In the preceding paper (Van Roozendael et al., 2006), the GDP 4.0 algorithm was described. In this paper, we deal with geophysical validation of the GDP 4.0 algorithm and the retrieved ozone products. We present results of a validation exercise involving comparisons of GDP 4.0 total ozone with the Network for Detection of Stratospheric Change (NDSC) and the World Meteorological Organization (WMO)/Global Atmospheric Watch (GAW) groundbased networks. We compare these results with similar validations of earlier GDP ozone products. We also present ground-based validation of TOMS versions 7 and 8 total ozone products, and we contrast these with GDP 4.0 values. On a global basis, GDP 4.0 total ozone results lie between À1% and +1.5% of ground-based values for solar zenith angles less than 70°; accuracy is now comparable to that obtainable from ground-based stations. At higher solar zenith angles in polar regions, larger discrepancies of up to +5% are found; in these regimes, errors on both satellite and ground-based measurements are higher. The validation also showed marked improvement in TOMS total ozone performance for the version 8 algorithm.Citation: Balis, D., et al. (2007), Ten years of GOME/ERS2 total ozone data-The new GOME data processor (GDP) version 4: 2. Ground-based validation and comparisons with TOMS V7/V8,

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