Improving cloud information over deserts from SCIAMACHY Oxygen A-band measurements

[摘要] The retrieval of column densities and concentration profiles of atmospherictrace 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 toretrieve trace gases in the atmosphere, is also capable of detecting clouds.FRESCO (Fast Retrieval Scheme for Clouds from the Oxygen A-band) is a fastand robust algorithm providing cloud information from the O₂ A-band forcloud correction of ozone. FRESCO provides a consistent set of cloud productsby retrieving simultaneously effective cloud fraction and cloud top pressure.The FRESCO retrieved values are compared with the SCIAMACHY Level 2operational cloud fraction of OCRA (Optical Cloud Recognition Algorithm) but,also, with cloud information from HICRU (Heidelberg Iterative Cloud RetrievalUtilities), SACURA (SemiAnalytical CloUd Retrieval Algorithm) and the MODIS(Moderate Resolution Imaging Spectroradiometer) instrument. The resultscorrelate well, but FRESCO overestimates cloud fraction over deserts. Thus,to improve retrievals at these locations, the FRESCO surface albedo databasesare decontaminated from the presence of desert dust aerosols. This isachieved by using the GOME Absorbing Aerosol Index. It is shown that thisapproach succeeds well in producing more accurate cloud information over theSahara.

[学科分类] 大气科学