A remote sensing-based integrated approach for monitoring grassland degradation: case study on the representative grassland near the middle and upper reaches of Heihe River Basin, Western China

The severity of grassland degradation in Shandan County, near the middle and upper reaches of Heihe River basin, western China was assessed through TM imagery in conjunction with in situ sampled grass parameters collected over 55 sampling plots of 1m². The above-ground biomass, vegetation fractional coverage of grassland, and palatable grass percent at each sampling plot was measured in assistance with the sampling method and on-the-spot investigations. The location of these sampling parameters was determined with a GPS receiver. Grassland degradation index (GDI) was developed based on these sampling parameters above. After radiometric calibration, the TM imagery was geometrically rectified. Vegetations indices were derived from TM imagery. Then, a grassland degradation monitoring model was established between TM bands-derived indices and GDI by using RS, GIS, and GPS techniques, field investigation and samples collection. Through the established regression model the TM imagery was converted into maps of grassland degradation. It was concluded that TM imagery, in conjunction with in situ grassland samples data, enabled the accurate assessment of grassland degradation in regional scale, and the integrated approach that allowed us to combine the different kinds of information from field survey records as well as remote sensing is efficient and simple in monitoring grassland degradation in quantity.