Three-dimensional forest light interaction model using a Monte Carlo method

A model for light interaction with forest canopies is presented, based on Monte Carlo simulation of photon transport. A hybrid representation is used to model the discontinuous nature of the forest canopy. Large scale structure is represented by geometric primitives defining shapes and positions of the tree crowns and trunks. Foliage is represented within crowns by volume-averaged parameters describing the structural and optical properties of the scattering elements. Simulation of three-dimensional photon trajectories allows accurate evaluation of multiple scattering within crowns, and between distinct crowns, trunks and the ground surface. The sky radiance field is treated as anisotropic and decoupled from bidirectional reflectance calculation. Validation has been performed on an example of dense spruce forest. Results show close agreement between model predictions and field measurements of bidirectional reflectance, high-resolution spectra and hemispherical albedo.