Analysis of NDVI Bidirectionality Based on SAILH Model
NDVI (Normalized Difference Vegetation Index) is an important vegetation index, extensively used to indicate vegetation status. But due to its anisotrapy or bidirectionality, there are many limitations when to develop the model between NDVI and vegetation parameters and the precision of madel is low. In order to develop reliable model, Lt is necessary to know about the bidirectionality of NDVI. SAILH model can model BRDF of vegetation canapy, so based an the BRDF of canopy the bidirectional distribution of NDVI can be calculated. The result shows that NDVI has very obvious bidirectionality or anisotropy and it can be influenced by different parameters such as LAI(Leaf Area Index) , LAD(Leaf Angle Distribution) , hot parameter,solar zenith and relative azimuth. The difference between bidirectional distribution of NDVI and BRDF is that NDVI has the smallest value in the hot spot , but canopy BRDF is contrary. In the principal plane, the value of NDVI in forward scattering direction is larger than in backward scattering direction. With the increase of LAI, the NDVI increases, but saturation occurs.When LAI is constant,other parameters can change the value and angle distribution of NDVI. Because the hot spot effect only occurs when observer is in the principal plane, bidirectionality of NDVI will weaken in other planes. The increase of solar zenith makes NDVI lower in the hot spat The increase of average leaf inclination angle makes NDVI increase in forward scattering direction, while NDVI in backward scattering changes very little.
NETL
NSTL
万方数据
维普
