Comparison NDVI with EVI in the herbage fresh weight estimation and vegetation dynamics for alpine grassland

NDVI (Normalized Difference Vegetation Index) and EVI (Enhanced Vegetation Index) were extracted from 126 MODIS images of 2007, 2008 and 2009, which were analyzed and compared with each other. This study indicated that the EVI values were lower than the NDVI values in the alpine meadow, and they all showed a similar trend in reflecting the growth status and characteristics of the vegetation, indicating that the EVI was more stable and accurate than the NDVI in alpine meadow by analyzing their corresponding standard deviation. Combined the alpine meadow AGB (Aboveground Green Biomass) data from 11 monitoring points, correlation analysis and regression analysis were applied to compare the two MODIS vegetation index products (NDVI, EVI) and four vegetation indices(NDVI250, NDVI500, EVI250, EVI500) in the alpine meadow AGB estimation. The results of this study showed that EVI estimated AGB more accurately than NDVI did, and had a better correlation relationship with AGB. EVI250 had the best dependent relation with alpine herbage fresh weight among four vegetation indices (NDVI250, NDVI500, EVI250, EVI500), and the correlation coefficient was 0.904 (P0.01). This study suggested that EVI250 was a better index in the alpine AGB estimation, and the regression equation between EVI250 and alpine herbage fresh weight was as following:yAGB=-244+1 316xEVI250.