Improving cloud information over deserts from SCIAMACHY Oxygen A-band measurements N. Fournier1, P. Stammes1, M. de Graaf1, R. van der A1, A. Piters1, M. Grzegorski2, and A. Kokhanovsky3 1KNMI, Climate Research and Seismology Department, De Bilt, The Netherlands 2Institute of Environmental Physics, University of Heidelberg, Germany 3Institute of Remote Sensing, University of Bremen, Germany
Abstract. The retrieval of column densities and concentration profiles of atmospheric
trace gas species from satellites is sensitive to light scattered by clouds.
The SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY
(SCIAMACHY) instrument on the Envisat satellite, principally designed to
retrieve trace gases in the atmosphere, is also capable of detecting clouds.
FRESCO (Fast Retrieval Scheme for Clouds from the Oxygen A-band) is a fast
and robust algorithm providing cloud information from the O2 A-band for
cloud correction of ozone. FRESCO provides a consistent set of cloud products
by retrieving simultaneously effective cloud fraction and cloud top pressure.
The FRESCO retrieved values are compared with the SCIAMACHY Level 2
operational cloud fraction of OCRA (Optical Cloud Recognition Algorithm) but,
also, with cloud information from HICRU (Heidelberg Iterative Cloud Retrieval
Utilities), SACURA (SemiAnalytical CloUd Retrieval Algorithm) and the MODIS
(Moderate Resolution Imaging Spectroradiometer) instrument. The results
correlate well, but FRESCO overestimates cloud fraction over deserts. Thus,
to improve retrievals at these locations, the FRESCO surface albedo databases
are decontaminated from the presence of desert dust aerosols. This is
achieved by using the GOME Absorbing Aerosol Index. It is shown that this
approach succeeds well in producing more accurate cloud information over the
Citation: Fournier, N., Stammes, P., de Graaf, M., van der A, R., Piters, A., Grzegorski, M., and Kokhanovsky, A.: Improving cloud information over deserts from SCIAMACHY Oxygen A-band measurements, Atmos. Chem. Phys., 6, 163-172, doi:10.5194/acp-6-163-2006, 2006.