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GOME Data Processor for level 0 to 1 and level 1 to 2 processing (GDP)

The potential of the GDP processors lies in the usefulness of them for the implementation of data processors for the instruments SCIAMACHY and GOME-2 on ENVISAT and MetOp, respectively. Unfortunately, the processors can't be used directly for this purpose. Level 0 to 1b processing is very much related to the specific instrument and its individual characteristics, so that only the experience which was gained during the development of this GDP processor may be applied. For the first version of level 1 to 2 algorithms as used in this GDP processor the “scientific" programming language FORTRAN was used. Therefore, also this processor needs to be totally re-implemented with a state-of-the-art programming environment (e.g. .C++)

The Global Ozone Monitoring Experiment (GOME) was originally conceived as a scaled-down version of the scanning spectrometer SCIAMACHY. It was given fast-track development status by ESA, and was launched on 21 April 1995 on board the second European Remote Sensing Satellite (ERS-2).

GOME is a nadir-viewing spectrometer covering the range 240-790 nm in 4 spectral channels. In its normal, Earth observation mode it scans across-track in three steps. The field of view of each step may be varied in size from 40 km x 40 km to 320 km x 40 km. The mode with the largest footprint (three steps with a total swath width of 960 km x 40 km) provides global coverage at the equator within 3 days - this is the default mode of operation.

In addition to the on-line components at the ground stations, the GOME Data Processors (GDP) are the operational off-line ground segment for GOME. GDP was developed and implemented at DFD with the help of several scientific institutions, and became operational in July 1996. It incorporates a Level 0 to 1 processing chain, the complete GOME data archive, a DOAS O3 total column retrieval process (Level 1to 2), and an image processing chain for the generation of higher-level products. The Level 1 and Level 2 data products are generated by DFD on behalf of ESA.

The level 1 products (calibrated spectra) are generated in a sort of compressed form. The end user has to apply an “extraction” software tool to obtain the final level 1 data. For the OASE system the processor and the extraction program have been combined.

Total column amounts of NO2, H2CO, SO2, OCIO and BrO have been retrieved successfully from GOME back-scatter measurements. The main algorithm in GDP level 1 to 2 processing is the DOAS (Differential Optical Absorption Spectroscopy) fitting for the retrieval of O3 and NO2 columns; this can be used directly as an OASE application.

Reported by

DLR-DFD (German Aerospace Centre, German Remote Sensing Data Centre)
Munchener Str. 20
D-82234 Wessling
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