A SEMIDISCRETE MODEL FOR THE SCATTERING OF LIGHT BY VEGETATION

An advanced bidirectional reflectance factor model is developed to acc ount for the architectural effects exhibited by homogeneous vegetation canopies for the first orders of light scattering. The characterizati on of the canopy allows the simulation of the relevant scattering proc esses as a function of the number, size, and orientation of the leaves , as well as the total height of the canopy. A turbid medium approach is used to represent the contribution to the total reflectance due to the light scattering at orders higher than 1. This model therefore inc orporates two previously separate approaches to the problem of describ ing light scattering in plant canopies and enhances existing models re lying on parameterized formulae to account for the hot spot effect in the extinction coefficient. Simulation results using this model compar e quite favorably with those produced with a Monte Carlo ray-tracing m odel for a variety of vegetation cases, The semidiscrete model is also inverted against a well-documented data set of bidirectional reflecta nce factors taken over a soybean canopy, It is shown that the inversio n of the model against a small subset of these measurements leads to r easonable values for the retrieved canopy parameters, These values are used in a direct mode to simulate the bidirectional reflectance facto rs for solar and viewing conditions significantly different from those available in the subset of soybean data and compared with the full se t of actual measurements.