Comparisons between in Situ Anisotropic Reflectance Measurements and Simulations for Vegetation Canopies: Validation and Sensitivity Analysis

In situ directional reflectance observations were taken on trees of three species and were used to validate the Four-Scale Linear Model for AnIsotropic Reflectance (FLAIR). FLAIR-simulated spectra were satisfactory in general, especially for the shaded and shaded/sunlit mixed portions of the canopy but were species dependent. Good agreements with field observations were found when utilizing these simulations to derive band ratio indexes, Normalized Difference Vegetation Index (NDVI) and Photochemical Reflectance Index (PRI). Sensitivity analysis were performed to investigate the importance of three canopy biophysical parameters, and the leaf to shoot ratio showed the most impact on simulation results. The results in this study showed the potential to simulate directional reflectances with FLAIR on canopies with complicated structure.