Clouds discrimination and surface classification for the sea ice albedo retrieval from MODIS data

The effect of Arctic sea ice on the radiative budget is of disproportional importance relative to its areal coverage. High albedo of sea ice is the driving force for a number of climatic feedbacks in the Arctic. In order to retrieve sea ice albedo from satellite and assess the state of the Arctic climate, important preparation steps are needed. They are the surface type classification and cloud clearing of the satellite scene. The MODIS sensor features spectral channels which can be used to distinguish all kinds of surfaces from snow-like surfaces, and further - separate snow, melting snow and ice, melt ponds and leads. In situ data is used to derive threshold values characterizing each family of surface types for MODIS bands 4 and 5. Separation of all the above mentioned snow-like surfaces from clouds is not a trivial task; MODIS bands 4, 5 and 6 are used to enhance the atmospheric reflectance in the NIR and screen out clouds from snow or ice-covered scene.