Landsat sign tau values 1990 2002 Tile 14 Jiapeng Qu Fabian Ewald fassnacht Christopher Schiller Teja Kattenborn Xinquan Zhao 10.6084/m9.figshare.7767809.v2 https://springernature.figshare.com/articles/dataset/Landsat_sign_tau_values_1990_2002_Tile_14/7767809 Landsat sign tau values 1990 2002 Tile 14 2019-05-22 09:09:42 Tibetan Plateau grassland LANDSAT Grassland trends ndvi-difference MODIS Mann-Kendall trend test