Abstract: Ozone total column (O3):

The Global Ozone Monitoring Experiment (GOME) was launched on April 1995 on board ESA's second European Remote Sensing Satellite (ERS-2).
This instrument can measure a range of atmospheric trace constituents, with the emphasis on global ozone distributions. Furthermore cloud properties and intensities of ultraviolet ... radiation are retrieved. These data are crucial for monitoring the atmospheric composition and the detection of pollutants.

DLR generates the operational GOME/ERS-2 level 1 and level 2 products on behalf ESA. GOME Near Real Time (NRT) products are available three hours after sensing. The NRT service was started in 1997 by setting up the GOME Data Processor at Kiruna station. Nowadays the GOME raw data is transmitted form all ERS-2 receiving stations, including the DLR Antarctic station at O'Higgins, to the DLR for further processing.

Algorithm:
The operational ozone total column products are generated using the algorithm GDP (GOME Data Processor) version 4.x integrated into the UPAS (Universal Processor for UV/VIS Atmospheric Spectrometers) processor for generating level 2 trace gas and cloud products.
The new improved DOAS-style (Differential Optical Absorption Spectroscopy) algorithm called GDOAS, was selected as the basis for GDP version 4.0 in the framework of an ESA ITT.
GDP 4.x performs a DOAS fit for ozone slant column and effective temperature followed by an iterative AMF/VCD computation using a single wavelength. The main improvements compared to GDP 3.0 are:
• Molecular Ring Correction parameterised [M. van Roozendael et al. (2006)]
• On-the-fly RTM simulations using LIDORT v3.3 [R. Spurr (2003)]
• Cloud Correction using OCRA and ROCINN v2.0 [D. Loyola et al. (2007)]
A description of the GDP 4.x algorithm and validation is given in the peer-review papers listed below. For more details see the reference documents listed in the GOME documentation and GOME-2 documentation pages.
The GDP 4.0 algorithm became operational for GOME/ERS-2 in 2004 after an independent geophysical validation [D. Balis et al. (2007)] showed that the average agreement of GDP 4.0 with correlative ozone column measurements was at the "percent level", that is, comparable to the precision level of ground-based sensors. GDP 4.0 became operational for SCIAMACHY/ENVISAT in 2006.
Further algorithm development was performed in the framework of EUMETSAT O3M-SAF where GDP 4.4 is the current operational algorithm for GOME-2/MetOp-A.

Acknowledgments:
GDP 4.x for total ozone retrieval is being developed by scientists from BIRA, RTS, AUTH and DLR and is funded by ESA, EUMETSAT O3M-SAF and national contributions.
The members of the GDP 4 Team are:
• BIRA: Michel Van Roozendael, Christophe Lerot, Jean-Christopher Lambert
• RTS: Rob Spurr
• AUTH: Dimitris Balis, MariLiza Koukouli
• DLR: Diego Loyola, Pieter.Valks, Nan Hao, Walter Zimmer
Special acknowledgments to Claus Zehner (ESA) for supporting the GDP 4 and GDP 5 projects and to Yakov Livschitz (now EUMETSAT) for the initial development of the UPAS system.