[Advances in the studies on topographic effects of vegetation indices.]

Vegetation index is a key indicator for qualitative and quantitative assessment of green vegetation, which has been widely used in vegetation monitoring. Forests are often distributed in mountainous areas with complex topography, which is one of the main factors of accurate retrieval of forest vegetation information. Here, we analyzed the topographic effects on canopy reflectance using a geometric optical model. The responses of complete ratio vegetation indices [simple ratio index (SR), normalized difference vegetation index (NDVI) and moisture adjusted vegetation index (MAVI)], incomplete ratio vegetation indices [enhanced vegetation index (EVI) and soil adjusted vegetation index (SAVI)], non-ratio vegetation indices [reduced simple ratio (RSR), modified normalized difference vegetation index (MNDVI), greenness vegetation index (GVI)] and, topography adjusted vegetation index [topography adjusted vegetation index (TAVI)] to topography were discussed in detail, with the aim to provide reference for selecting vegetation index in complex terrain mountainous area. The shortcomings of current literatures about the topographic effects on vegetation indices were analyzed and the future research directions were prospected.