Directional vegetation index and its effects on normalized difference vegetation index based agricultural applications

摘要

The directional normalized difference vegetation index (NDVI) was calculated by using field measured spectral data of the winter wheat canopies at the crop different growth and development stages. In the principal plane, the hotspot and directional NDVI were analyzed. The relationships between NDVI and leaf area index (LAI) were developed, and the effects of the directionality on vegetation index based applications were discussed as well. Considering the reflectance changes near the hotspot for the two winter wheat cultivars which have a horizontal leaf type and an erectile leaf type, respectively, we find spectral reflectances of the red and near-infrared bands at the hotspot are slightly higher than those near the hotspot. However, NDVI at the hotspot is significantly lower than that near the hotspot. The regression analysis results between NDVI and LAI show that there are significant exponent correlations between directional NDVI and LAI for the two cultivars. However, the coefficients of the exponent equations and the correlation coefficients are varied with the viewing zenith angles, and the correlation coefficients for the two wheat canopy types are also varied at a given viewing angle. These results indicate the directionality of NDVI should be considered for NDVI based agricultural applications.