Umkehr Ozone Profile Analysis and Satellite Validation

High quality and vertical resolution profiles of ozone that cover both troposphere, UTLS and the stratosphere, can be obtained by Brewer and Dobson spectrophotometers in a special viewing mode called Umkehr. As a result, this type of observations can be used in the validation of both satellite IR instrumentation, that cover from the UTLS upwards, as well as UV instrumentation, that also cover the troposphere albeit with a coarser vertical resolution.

Within the IDEAS+ framework new efforts have been made to improve the operational Umkehr analysis algorithm and provide a more robust and unique validation dataset for ozone profile observations by space-born sensors such as S5P/TROPOMI, as well as GOME2 and IASI instruments on the Metop platforms.

Within this work, Dobson and Brewer Umkehr retrieval methods have been optimized and applied to Umkehr ozone profile measurements for a number of selected ground-based stations. Umkehr observations were then compared to satellite ozone profile measurements from the merged NOAA Solar Backscatter UV ozone profiles, as well as those by the Global Ozone Monitoring Experiment (GOME-2) instruments on board the EUMETSAT Metop platforms.

In the following sections, the Umkehr observations retrieval methodology is briefly explained, the particular settings used in each type of instrument, Brewer and Dobson so as to perform Umkehr measurements are given, and the optimization methodology of the measurements is separately described. The results section comprises of the final updated time series of Umkehr observations for 4 Brewer and 4 Dobson stations, and first comparisons of the optimized Umkehr profiles to SBUV and GOME2 satellite measurements in the form of case studies for Thessaloniki, Greece (Brewer) and Lauder, New Zealand (Dobson). Finally, some additional comparisons of the optimized Dobson data with models (Modern-Era Retrospective Analysis for Research and Applications, Version 2, Global Modeling Initiative, M2GMI and the CTM model Global Modelling Initiative MERRA2, GMI-MERRA2), complimentary satellite observations (Aura MLS, S-NPP OMPS, SBUV and SAGE III/ISS records) and co-located ozonesonde records are analyzed (Petropavlovskikh et al., 2021). The comparisons to all available satellite data are used to provide confirmation of the Umkehr data quality and to establish their suitability for future validation of ozone profiles products from various satellites, such as TROPOMI/S5P.