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

[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) ground-based 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 -1% and +1.5% of ground-based values for solar zenith angles less than 70 degrees; 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.