Distinction between clouds and ice/snow covered surfaces in the identification of cloud-free observations using SCIAMACHY PMDs

[摘要] SCIAMACHY on ENVISAT allows measurement of differenttrace gases including those most abundant in the troposphere (e.g. CO₂, NO₂, CH₄, BrO, SO₂).However, clouds in the observed scenes can severely hinder theobservation of tropospheric gases.Several cloud detection algorithms have been developed for GOME onERS-2 which can be applied to SCIAMACHY.The GOME cloud algorithms, however, suffer from the inadequacy ofnot being able to distinguish between clouds and ice/snow coveredsurfaces because GOME only covers the UV, VIS and part of the NIRwavelength range (240-790 nm).As a result these areas are always flagged as clouded, and therefore often not used.Here a method is presented which uses the SCIAMACHY measurements inthe wavelength range between 450 nm and 1.6 µm to make adistinction between clouds and ice/snow covered surfaces.The algorithm is developed using collocated MODIS observations.The algorithm presented here is specifically developed to identify cloud-freeSCIAMACHY observations.The SCIAMACHY Polarisation Measurement Devices (PMDs) are used forthis purpose because they provide higher spatial resolutioncompared to the main spectrometer measurements.

[学科分类] 大气科学