Detecting Vegetation Fractional Coverage of Typical Steppe in Northern China Based on Multi-scale Remotely Sensed Data Monitoring and Analysis of Vegetation Fractional Cover in Changsha-Zhuzhou-Xiangtan Core Region Based on Remote Sensing Data Improvement, Comparison, and Application of Field Measurement Methods for Grassland Vegetation Fractional Coverage The synthetically estimating vegetation fractional coverage of grassland using field data and ASTER remote sensing imagine