Landsat sign tau values 1990 2002 Tile 9 Jiapeng Qu Fabian Ewald fassnacht Christopher Schiller Teja Kattenborn Xinquan Zhao 10.6084/m9.figshare.7767800.v2 https://springernature.figshare.com/articles/dataset/Landsat_sign_tau_values_1990_2002_Tile_9/7767800 Landsat sign tau values 1990 2002 Tile 9 2019-05-22 09:09:41 Tibetan Plateau grassland LANDSAT Grassland trends ndvi-difference MODIS Mann-Kendall trend test