Design and implementation of the GOME Data Processor

ERS-2 is intended to provide data continuity between ERS-1 and the European polar platforms. In addition to the mission objectives of ERS-1, ERS-2 is intended to make a significant contribution to atmospheric chemistry. Thus, in addition to the instruments on ERS-1, it will also carry the Global Ozone Monitoring Experiment (GOME). This instrument is intended to measure a range of atmospheric trace constituents both in the troposphere and in the stratosphere. GOME is a nadir-viewing spectrometer which in its normal mode scans across-track in three steps. The field of view may be varied in size from 120 km×40 km to 960 km×40 km. The mode with the largest footprint will provide global coverage at the equator within 3 days. In most instances the GOME instrument will measure the concentrations of trace gases as total column densities. The notable exception is ozone for which, in addition, vertical profiles can be obtained. Ozone distributions may be derived in two ways, namely the traditional “backscatter” approach (similar to that used by existing instruments such as the Solar Backscatter Ultraviolet (SBUV)), and the Differential Optical Absorption Spectroscopy (DOAS) technique which would yield ozone column values. GOME will demonstrate the feasibility of using the differential absorption technique to observe trace constituents including ozone. Existing nadir-viewing instruments such as SBUV exploit the fact that the height at which solar radiation is back scattered by the atmosphere varies with wavelength. However, this approach depends in contradiction to DOAS on an accurate radiometric calibration. Besides the on-line components at the ground stations and the Mission Management and Control Centre (MMCC) the GOME Data Processor (GDP) system will be the operational off-line ground segment for GOME. It will incorporate a Level 0 to 1 processing chain, the complete GOME data archive, a DOAS 03 total column retrieval process and an image processing chain for the generation of higher-level products