Estimation and Uncertainty Analyses of Fractional Vegetation Cover (FVC) over Mountain Area

Fractional Vegetation Cover (FVC) is one of the canopy structure parameters which plays an important role in climatic, hydrologic, and geochemical cycles and is widely used to describe global environment change. It is especially important in forest structure, ecosystem, and fire monitoring research. However, most forests are located over the complex terrain areas, e.g. mountain areas, where the topographic effect has a great influence on the accuracy of FVC estimation. In this study, the uncertainty of FVC estimation over mountain areas is analyzed and an improved method is proposed for the FVC estimation. A vegetation canopy radiative transfer model with hotspot and topography consideration is involved to analyze the uncertainty of FVC estimation accuracy. An improved radiative transfer-geometric optical vegetation model is used to estimate FVC over mountain areas by establishing the relationship between FVC and four scene components in geometric optical. Results show that: 1) the topographic effect influences varies vegetation indices (VIs) differently and the difference between VIs with and without topographic effect can up to 35% (relative error) and this can cause about 10% relative error of FVC estimation; 2) the proposed FVC estimation method can effectively resistant topographic effect. The uncertainty and difficulty of obtaining the FVC over mountain areas hamper the further application of FVC to achieve a high accuracy in forest research. The advantage of the proposed method is prominent in an area where terrain is complex. The method is flexible to be implemented over regional or global scales and to generate FVC maps.