An analysis of fractional vegetation cover of the Gannan grassland in the non-growing season based on Multispectral data and small UVAs

Vegetation from non-growing seasons is a vital animal feed type for livestock in winter and spring. Therefore, estimates of the livestock carrying capacity of local ranches are important for studying non-growing season vegetation. In this paper, Gannan prefecture was taken as the research area, and 60 m × 60 m digital photos of non-growing season vegetation of the prefecture’s grasslands were obtained via cameras mounted on small unmanned aerial vehicles (UVAs). The non-growing season vegetation coverage was obtained by a supervision classification from digital photos. Using the MODIS/Terra + Aqua bidirectional reflection distribution function and the hemispheric reflectivity product of MCD43A4 together with the Landsat8 OLI image data, the soil tillage index (STI), dead fuel index (DFI), and normalized difference tillage index (NDTI) a total of 9 vegetation indexes were calculated. By analyzing the correlations between different vegetation indexes and fractional vegetation cover (FVC), a regression model of grassland FVC in the non-growing season was established; then, the accuracy of model was evaluated to compare the ability of different data sources that can most accurately estimate the FVC. The results show that: 1) Landsat8 OLI data is more suitable than MODIS data for studying FVC during the non-growing season in the Gannan grasslands; 2) NDTI is the best index for non-growing season FVC estimations in the study area, and its linear estimation model of y = 1 432.074x – 166.855 (R² = 0.407) is the optimal inversion model of FVC in the non-growing season; 3) From April to May in 2018, Gannan has a high FVC in the west and a low FVC in the east; coverage rates in most regions ranges from 20% to 50%, with only the rates in the north part of Xiahe, the central part of Hezuo and the southeast part of Maqu being less than 20%. The coverage rate in the northeast part of Maqu is over 60%. This study can provide a basis for calculating the seasonal livestock carrying capacity in Gannan prefecture.