Detecting vegetation change during the period 1998-2002 in NW China using SPOT-VGT NDVI time series data

The primary objective of this study was to assess the trends of vegetation changes in west of China since 1998 to 2002 with the 1 km²-resolution SPOT-Vegetation 10-day maximum-value synthesized normalized difference vegetation index (NDVI) data. The framework for the analysis is the use of the coefficient of variation (COV) of the decadal NDVI as a measure of vegetative biomass change. A higher NDVI COV for a given pixel represents a greater change in vegetation biomass in the ground area represented by that pixel. And then a linear regression was used to determine the trend of COV value for each pixel over the 5-year period. The slope of the linear regression can be gained and acted as the criterion for the change direction. Pixels with a negative slope are considered to represent ground areas with decreasing amounts of vegetation, vice versa. Results showed vegetation ecosystems in west of China are undergoing accelerated change due to natural and anthropogenic disturbances since 1998 had the increase trends in the five years.