UPAS / GDOAS 4.0 Upgrade of the GOME Data Processor for Improved Total Ozone Columns

The Global Ozone Monitoring Experiment (GOME) on board ERS-2 (launched in April 1995) is the successful predecessor of a series of new generation sensors (SCIAMACHY, OMI, GOME-2) aiming at the needed global measurement of key ozone-related species to assess current and future changes of the atmosphere [1-3]. Providing the global picture of atmospheric ozone (O 3), GOME is also the first orbiting instrument having the capability to measure the vertical column amount of nitrogen dioxide (NO 2), a trace species playing a crucial role in the ozone photochemistry. Since August 1996, GOME total O 3 and NO 2 column data are routinely processed at the German Processing and Archiving Facility (D-PAF) established at the German Aerospace Centre (DLR) on behalf of ESA with the GOME Data Processor (GDP) [4-6]. Since the release in summer 1995 of its first developmental version, GDP was upgraded on many occasions and the quality of both ozone and NO 2 products has improved significantly (e.g., [7,8]). GOME has now been producing global distributions of total ozone for nine years. The length of this data record makes it desirable for use in long-term ozone trend monitoring, for which a crucial requirement is the ability to measure 1-% changes in total ozone concentrations globally and over a period of 10 years. Such a level of accuracy had not been met yet with GDP version 3.0 [9]. To this end, ESA-ESRIN issued an Invitation to Tender (ITT) in June 2002 to develop improved GOME total ozone column retrieval algorithms capable of producing trend-quality data. Three consortia were awarded contracts to perform this work in competition. The Final Review Board met in December 2003, and a further delta validation was finished in January 2004 [10]. Following the Board's recommendations, the GDOAS algorithm (developed jointly by the Belgian Institute for Space Aeronomy, BIRA-IASB, and the Smithsonian Astrophysical Observatory, SAO) was selected for operational implementation in the D-PAF at DLR as part of the ESA ERS Ground Segment. On the operational side, the GDP environment at D-PAF, designed in the early 1990s, was replaced recently by a more flexible environment called Universal Processor for UV/VIS Atmospheric Spectrometers (UPAS). GDP 4.0 replaces version 3.0 of GDP since November 2004 and the reprocessed GOME data record, including historical data, is already available to the public via the ERS Help & Order Desk (see GOME Data Disclaimer 2004 in Annexe). The UPAS/GDOAS project covers …