GOST2: The Improvement of the Canopy Reflectance Model GOST in Separating the Sunlit and Shaded Leaves

Accurately simulating the area ratios of the sunlit and shaded foliage in multiple-view angles presents a challenge in developing a geometric-optical (GO) model. GOST model by Fan et al.[1] proposed a high computationally demanding ray tracing method on this issue. In order to relax the computational restriction, a new hybrid canopy reflectance model GOST2 based on GOST is developed with a “ray tracing + GO” method, which is used for simulating the area ratios of the sunlit and shaded foliage. GOST2 shows the explicitly physical mechanism and has the capability in modeling the area ratios of the sunlit and shaded foliage on slopes. The area ratios of the four scene components of the five GO models, such as GOST2, GOST, the Li-Strahler model, the four-scale model, and Unified, are quantitatively evaluated. The canopy reflectances by the five GO models and the three-dimensional virtual canopy model are validated by the observed reflectance. It indicates that GOST2 is both reliable and computationally undemanding canopy reflectance model.