The Determination of the Cloud Fraction in the Sciamachy Pixels Using Meris

The cloud fraction is an important atmospheric product needed for an accurate determination of trace gas concentrations and also cloud and aerosol properties from space-borne optical measurements. In this paper we develop a technique to determine the cloud fraction in the Scanning Imaging Absorption Spectrometer for Atmospheric ChartographY (SCIAMACHY) ground scenes (30x30 km and even larger ground footprints depending on the channel and the location of measurements) using simultaneous MEdium Resolution Imaging Spectrometer (MERIS) observations (1x1 km ). MERIS and SCIAMACHY are placed on the same satellite (ENVISAT). The results of newly developed SCIAMACHY cloud fraction retrieval algorithm are compared with correspondent MERIS imagery. In addition to MERIS data, also SCIAMACHY Polarization Measurements Devices (PMDs) and reflectances are used to enhance the retrievals in the case of bright surfaces (snow and ice fields, deserts). 2