The global ozone monitoring experiment (GOME): Mission concept and first scientific results

The Global Ozone Monitoring Experiment (GOME) is a new instrument aboard th e European Space Agency's (ESA) Second European Remote Sensing Satellite (E RS-2), which was launched in April 1995. The main scientific objective of t he GOME mission is to determine the global distribution of ozone and severa l other trace gases, which play an important role in the ozone chemistry of the earth's stratosphere and troposphere. GOME:measures the sunlight scatt ered from the earth's atmosphere and/or reflected by the surface in nadir v iewing mode in the spectral region 240-790 nm at a moderate spectral resolu tion of between 0.2 and 0.4 nm. Using the maximum 960-km across-track swath width, the spatial resolution of a GOME ground pixel is 40 X 320 km(2) for the majority of the orbit and global coverage is achieved in three days af ter 43 orbits. Operational data products of GOME as generated by DLR-DFD, the German Data Processing and Archiving Facility (D-PAF) for GOME, comprise absolute radio metrically calibrated earthshine radiance and solar irradiance spectra (lev el 1 products) and global distributions of total column amounts of ozone an d NO2, (level 2 products), which are derived using the DOAS approach (Diffe rential Optical Absorption Spectroscopy). (Under certain conditions and som e restrictions, the operational data products are publically available from the European Space Agency via the ERS Helpdesk.) In addition to the operational data products, GOME has delivered important information about other minor trace gases such as OClO, volcanic SO2, H2CO from biomass burning, and tropospheric BrO. Using an iterative optimal esti mation retrieval scheme, ozone vertical profiles can be derived from the in version of the UV/VIS spectra. This paper reports on the GOME instrument, i ts operation mode, and the retrieval techniques, the latter with particular emphasis on DOAS (total column retrieval) and advanced optimal estimation (ozone profile retrieval). Observation of ozone depletion in the recent polar spring seasons in both h emispheres are presented. OClO observed by GOME under twilight conditions p rovides valuable information on the chlorine activation inside the polar vo rtex, which is believed to be responsible for the rapid catalytic destructi on of ozone. Episodes of enhanced BrO in the Arctic, most likely contained in the marine boundary layer, were observed in early and late spring. Exces s tropospheric nitrogen dioxide and ozone have been observed during the rec ent Indonesian fire in fall 1997. Formaldehyde could also clearly be identi fied by GOME and is known to be a by-product resulting from biomass burning .