Changes of forage biomass of grasslands during the growing season in the Qinghai-Tibetan Plateau based on MODIS data

Grassland biomass is an important indicator to evaluate the ecological vulnerability and sensitivity,and is also an important indicator to assess the grassland degradation.In this study,the NDVI index and EVI index from MODIS data and the field data from 326 plots in the grassland were used to establish and optimize the prediction models of grassland biomass for different grassland types,and then established model was applied to estimate the annual and monthly grassland biomass during the period from 2002 to 2009.This study showed that the alpine meadow biomass retrieval model was y=6.202 5x2-574.89x+14 586,here,x was NDVI;alpine steppe biomass retrieval model was y=0.1 665 5x17 732,here,x was EVI.The biomass of alpine steppe and meadow showed a fluctuant trend during the period 2002-2009,and the fluctuation range of alpine meadow was bigger than that of alpine steppe.The biomass of alpine steppe and meadow increased from June to August,and decreased from August to September,the fluctuation range of alpine steppe was bigger in July and smaller in August than that of alpine meadow,however,the fluctuation range in June and September was not obvious between alpine meadow and alpine steppe.