MODELING BIDIRECTIONAL REFLECTANCE OF MULTICOMPONENT VEGETATION CANOPIES

By combining geometrical optics and transport theory, a bidirectional reflectance model for multicomponent vegetation canopies is explicitly developed in this article. A precise expression of the overlap functi on, is derived for vertically cylindric phytoelements randomly distrib uted in the canopy, and a mathematical model for describing the vertic al distribution of leaf area density is presented and fitted with meas ured data. In addition, the size, shape, orientation, and nonrandom di stribution of leaves and vertical inhomogeneity of the canopy are prop erly taken into account in this model. The model also reproduces the m easured distributions of reflectance from a wheat canopy quite well. T he significant effect of stems on the canopy reflectance is identified by comparison with the result of the corresponding leaf canopy model. The results of sensitivity analysis prove that, even for crop canopie s like wheat in this study, the influence of stems cannot be neglected if the ratio of stem silhouette area to the total foliage area is gre ater than 10%. Since this multicomponent model is a hybrid one, it cou ld serve as a primary model to develop more accurate reflectance model for inhomogeneous vegetation canopies, such as forest, in further stu dies.