Validation of GOME with ground-based ozone measurements at Uccle (Belgium)

E. Schoubs and D. De Muer Royal Meteorological Institute of Belgium, Ringlaan 3, B-1180 Brussels, Belgium els@oma.be

Abstract

Total ozone measurements from a Dobson and a Brewer spectrophotometer at Uccle (50º48'N, 4º21'E) are compared with the ozone data from GOME during the daily overpasses of the satellite. The quality of the ground-based data is ensured through regular calibration checks and through recent comparisons with the world standard instruments. Electrochemical ozone soundings performed at our station give the opportunity for validation of the ozone vertical column density below the cloud cover.

The data obtained from July to November indicate that the mean differences (+/- standard deviation) between the GOME and the Dobson and Brewer ozone data amount to -1.0 +/- 4.5% and -1.3 +/- 4.5% respectively. These mean differences show no statistically significant dependence on the air mass factor (amf) for values of amf up to 3.7. For larger amf values the GOME data tend to be much lower than ground-based ozone data. On the other hand, for small total ozone amounts (below about 250 Dobson Units) GOME data are in general larger than ground-based data. We have found a small dependence of the mean difference on the cloud cover fraction (CCF) of the GOME pixels. With the Brewer as well as the Dobson spectrophotometer a mean difference of -2% was found for CCF=0, the GOME data being the lowest, while it is virtually zero for CCF=1.

From Meteosat images and from temperature and humidity profiles of the correlative ozone soundings it appears that the mean cloud top pressure and the mean vertical column density of ozone below the cloud cover used in the GOME algorithm are correct. However, the day to day variations are not well described by the algorithm.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry