[Performance evaluation of GIMMS NDVI based on MODIS NDVI and SPOT NDVI data]

The study evaluated GIMMS NDVI based on MODIS NDVI and SPOT NDVI over the same period from 2000 to 2015. We assessed their absolute values, dynamics, trends and cross-relationships between any two of the NDVIs for the national scale, as well as four separate land use types, i.e., paddy field, dry land, forest, and grassland. GIMMS NDVI was numerically greater than MODIS NDVI and SPOT NDVI. The three NDVIs exhibited equal capability of capturing monthly phenological variations. During the study period, the three NDVIs showed increasing trends in most regions, with GIMMS NDVI showing the smallest increment. Pronounced differences were identified in trends between GIMMS NDVI and MODIS NDVI or SPOT NDVI in the northwest, northeast, south-central China, Tibetan Plateau and Yunnan-Guizhou Plateau, implying that GIMMS NDVI trends in these regions should be interpreted with caution. High correlations existed between the three datasets. MODIS NDVI and SPOT NDVI showed stronger correlations at national scale. The GIMMS NDVI and MODIS NDVI were in highest accordance for dry land, while MODIS NDVI and SPOT NDVI were in higher accordance for the paddy field, forest, and grassland than dry lands.