First Results on the DOAS-Retrieval of OClO from SCIAMACHY Nadir Measurements
2005
The Scanning Imaging Absorption Spectrometer for
Atmospheric Chartography was launched successfully
onboard ENVISAT on March 1, 2002. It observes solar
radiation transmitted, backscattered from the atmosphere
and reflected from the ground in nadir, limb and occultation
viewing modes. Chlorinedioxide (OClO), an important
indicator for stratospheric chlorine activation, can be
measured in the UV spectral range by Differential Optical
Absorption Spectroscopy (DOAS).
First results of the DOAS retrieval of OClO slant column
densities (SCDs) from the SCIAMACHY measurements
are presented. The influence of several parameters like the
wavelength range chosen as fitting window or the reference
spectra included in the fit on the quality of the retrieval is examined. It is found that a proper correction of
polarisation features in the spectra is essential for a good
DOAS analysis of OClO. The OClO SCDs derived from SCIAMACHY are compared to measurements of the Global Ozone Monitoring Experiment (GOME) which has successfully measured OClO since 1995. SCIAMACHY flies in the same orbit, but measures approx. 30 minutes earlier than GOME. As OClO shows a strong diurnal variation, this leads to differences in the observed column densities, which may be useful to investigate the photochemistry of OClO and related compounds. Also, the spatial resolution of SCIAMACHY is higher (30*60 km^2 compared to 40*320 km^2 for GOME), which will allow a more detailed study of small scale effects like e.g. chlorine activation in mountain waves.
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