Annual Total Gross Primary Production Estimation based on Vegetation Indices Seasonal Variation Curve

For the estimation of annual Gross Primary Productivity(GPP)，it is proposed an estimation method with simple parameters and small errors.By taking each type of vegetation in the area of Three-North Shelterbelt Program(TNSP) as the research subject，the MODIS vegetation indices were obtained，and the seasonal variation curve of vegetation indices were built.Then，the fitting relation between the integral of time series vegetation indices(ΣVIs) and GPP products of MODIS was established，so as to realize a simple GPP estimation method and study the applicable ΣVIs for estimating the GPP of all vegetation types.The results show that：(1) ΣVIs is suitable for estimating the annual total GPP in research area and significantly correlated with MODIS GPP at the confidence level of p<0.01;(2) ΣEVI2 is applicable to estimate the GPP of evergreen needleleaf forest，decidious needleleaf forest，decidious broadleaf forest，mixed forest，woody savannas，savannas，permanent wetlands，croplands，croplands/natural vegetation mosaic，while the effect of ΣNDVI for estimating the GPP of closed shrublands，open shrublands，grasslands，croplands，and barren or sparsely vegetated is superior to ΣEVI andΣEVI2;(3) Since the NDVI itself is saturated in the area of high Leaf Area Index(LAI)，the error of estimating the GPP of high LAI vegetation type by ΣNDVI is larger，while using ΣEVI and ΣEVI2 to estimate them has better accuracy，and the limitation from blue band of EVI2 reduces compared with EVI，which can be applied to the GPP research of long time series better.