Applicability of MODIS and VIIRS vegetation index products in estimating grassland biomass in Gannan

At present, the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor is in the extended service stage. The First Visible Infrared Imager Radiometer Suite (VIIRS) sensor is a further development of the MODIS sensor. With Gannan region as an example, the Enhanced Vegetation Index (EVI), provided by four vegetation cover products of MODIS and two vegetation cover products of VIIRS, were selected in this study. The EVI and Normalized Difference Vegetation Index (NDVI) were used to analyze the difference between MODIS and VIIRS in grassland above-ground biomass estimation. The main conclusions are as follows: 1) Compared with VIIRS, the accuracy of the MODIS-based grassland above-ground biomass inversion model in the Gannan region was higher, and MODIS MOD13A1 is more suitable for the estimation of grassland above-ground biomass in the Gannan region. 2) The areas with higher aboveground biomass (> 3000 kg·ha⁻¹) were mainly distributed in Maqu, Luqu, and Hezuo; while the areas with lower aboveground biomass (< 1500 kg·ha⁻¹) were mainly distributed in Xiahe and Dibu. The aboveground biomass of grassland in the western region was higher than that of the non-grassland in the eastern region. 3) The areas with large biomass increase were mainly distributed in the north of Xiahe, the northwest of Maqu, and the middle of Luqu; while the areas with large biomass decrease were mainly distributed in the southeast of Maqu and the south of Luqu.