ESA's ten-instrument Envisat, the world's largest satellite for environmental monitoring, was launched in February 2002. Its onboard Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument records the spectrum of sunlight shining through the atmosphere. These results are then finely sifted to find spectral absorption 'fingerprints' of trace gases in the air. Nitrogen dioxide (NO2) is a mainly man-made gas, excess exposure to which causes lung damage and respiratory problems. It also plays an important role in atmospheric chemistry, because it leads to the production of ozone in the troposphere which is the lowest part of the atmosphere, extending up to between eight and 16 kilometres high.

Nitrogen dioxide is produced by emissions from power plants, heavy industry and road transport, along with biomass burning. Lightning in the air also creates nitrogen oxides naturally, as does microbial activity in the soil. Localised in-situ measurements of atmospheric nitrogen dioxide are carried out in many western industrial countries, but ground-based data sources are generally thin on the ground.

Space-based sensors are the only way to carry out effective global monitoring: the first satellite sensitivity to tropospheric nitrogen dioxide was demonstrated with the Global Ozone Monitoring Experiment (GOME) on ESA's ERS-2. However GOME was only a sub-scale precursor of the German, Dutch and Belgian financed SCIAMACHY flying on Envisat.

While both instruments function in the same way, GOME has a limited spatial resolution of only 320 x 40 km, compared to a typical 60 x 30 km with SCIAMACHY, which also observes the atmosphere in two different views downwards or 'nadir' looking as well as making 'limb' observations in the direction of flight and has a significantly larger spectral range than its predecessor.

Teams from the Universities of Bremen and Heidelberg in Germany, the Belgian Institute
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Contact: Mariangela D'Acunto
mariangela.d'acunto@esa.int
39-069-418-0856
European Space Agency
11-Oct-2004

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