MODIS-NDVI-based mapping of the length of the growing season in northern Fennoscandia - Karlsen, S.-R.; Tolvanen, A.; Kubin, E.; Poikolainen, J.; Hogda, K.A.; Johansen, B.; Danks, F.S.; Aspholm, P.; Wielgolaski, F.-E.; Makarova, O.