Continental use of SCAmod fractional snow cover mapping method in boreal forest and tundra belt

The method SCAmod for fractional snow cover (FSC) retrieval for Northern Eurasia boreal forest zone and tundra is presented, together with the accuracy assessment using high resolution Landsat TM/ETM+ data as a reference. Employing an apparent forest transmissivity, SCAmod accounts for forest canopy effect into the observed reflectance. Today, the method is implemented for Northern Hemisphere Snow extent production in European Space Agency DUE-project GlobSnow. It is therefore interesting to assess SCAmod performance in continental scale. We apply SCAmod to MODIS and compare the result with FSC derived from TM/ETM+ imagery over selected areas. Also validation against Finnish ground truth data is presented. Results indicate that high resolution data-derived FSC can be used to represent the ground truth, but this depends on the size and spatial distribution of snow-free patches as well as on the forest density in the target area. In dense forests, TM/ETM+ FSC showed strong underestimation, implying that these data cannot be used to represent the ground truth but only as suggestive reference.