Crop biomass estimation in irrigated agricultural areas, Northwestern China using MODIS vegetation indices

Based on field survey data, MODIS Enhanced Vegetation Index(EVI) image acquired in 2005 was applied for crop biomass estimation in Ebinur lake area. A total of 75 plots were investigated and the relationship between biomass and vegetation indices was clarified. A series of regression models comparing biomass and EVI were established. The sequence of correlation coefficients from high to low was power regression>exponential regression>polynomial regression>linear regression. The tested result by expressing with power regression model gave more accurate estimation(r=0.78). A crop biomass distribution map was derived, the crop biomass was higher in irrigated areas (between 1 kg/m2 and 10 kg/m2) and lower in non-irrigated areas (less than 1 kg/m2 )，indicating that the local crop biomass is mainly influenced by agricultural irrigation conditions.