SO2 Retrieval from SCIAMACHY using the Weighting Function DOAS (WFDOAS) technique: comparison with Standard DOAS retrieval C. Lee1,*, A. Richter1, M. Weber1, and J. P. Burrows1 1Institute of Environmental Physics and Remote Sensing, University of Bremen, Bremen, Germany *now at: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada
Abstract. Atmospheric SO2 can be measured by remote sensing of scattered sunlight
from space, using its unique absorption features in the ultraviolet region.
However, the sensitivity of the SO2 measurement depends critically on
spectral interference, surface albedo and varies with wavelength as Rayleigh
scattering increases at shorter wavelengths. The Weighting Function
Differential Optical Absorption Spectroscopy (WFDOAS) method was used to
pinpoint these problems and improve the retrieval. The Ring spectra included
in the WFDOAS fit were determined as a function of total ozone column
density, solar zenith angle, surface albedo, and effective scene altitude.
The WFDOAS SO2 retrieval from SCIAMACHY (Scanning Imaging Absorption
Spectrometer for Atmospheric Chartography) data onboard the ENVISAT
satellite are presented here and compared to those of the Standard DOAS
(SDOAS) method for cases of background conditions and volcanic eruption. The
study demonstrates the problems in the SO2 retrieval with SDOAS, such
as the positive offsets over remote (clean) regions and the negative offsets
at high solar zenith angles and high ozone, could be attributed to imperfect
correction for the varying ozone dependence of the Ring effect and could be
solved by the WFDOAS approach.
Citation: Lee, C., Richter, A., Weber, M., and Burrows, J. P.: SO2 Retrieval from SCIAMACHY using the Weighting Function DOAS (WFDOAS) technique: comparison with Standard DOAS retrieval, Atmos. Chem. Phys., 8, 6137-6145, doi:10.5194/acp-8-6137-2008, 2008.