Influence of Vegetation Structure and Sun /View Geometry on NDVI
植被结构及太阳／观测角度对NDVI的影响

A comprehensive, analytical model for calculating bidirectional reflchnce factor(BRF) of multicomponent vegetation canopies 1] is employed to study the influence of canopy spatial stricture on the commonly used normaled difference vegetation index(NDVI). The dependencies of NDVI on leaf (or other forliage elements) angle distribution(LAD), dimension of foliage elements(e.g., leaf), foliage dispersion mode and the areal feac tion of non-leaf organs are discussed, and the variation of NDVI with solar /viewing zenith is examined. The result shows that the spatial inhomogeneity of canopy architecture and the optical properties of foliage elements siedficanhy affect the magnitude and angular distribution of NDVI for canopies even with a fixed leaf area index (LAI) Usually, the angular variation of NDVI is pronounced. And it is unlikely to correctly estimate LAI through NDVI without a prior knowledge of the spatial dispersion mode of foliage elements or if the optical properties of different foliage elements much differ. But for a canopy consisting of randomly dispersed foliage elements, effects of other architectural parameters of canopy on LAI estimation can be minimized by using spectral data far away from the hotspot direction.