A model for thermal IR exitance of a plant canopy based on Monte Carlo simulation of photon transport isdeveloped. The canopy is defined by leaf area index

leaf angle distribution

and leaf area profile. Canopy is dividedinto some layers by layer density. Every layer can have itself leaf area index and leaf angle distribution. Soil and leaf areassumed as Lambertian source

and they also do Lambertian response for photon scattering. The Monte Carlosimulation included mutli-scattering of photon. The LSF conceptual model of effective emissivity for non-isothermalsurface is validated. Simulation showed that the multi-scattering between components and component temperaturedifferences of a canopy are two key factors for directional thermal emission of the canopy. Component temperaturedifferences influence effective emissivity weakly

thus the effect can be ignored.