Three Dimensional Canopy Radiation Transfer Model Based On Monte Carlo Ray Tracing

To Understand the mechanism of radiation transfer in plant canopy is crucial in studying and simulating the plant growth process. More and more interests are focused on the modeling of radiation transfer in plant canopy in the research fields such as quantified remote sensing of vegetation, virtual plant and visualization of plant.In this study, Monte Carlo ray tracing was employed to model the radiation transfer within three dimensional plant canopies. Triangles were used as primary facets to construct the architecture of the canopy. Bidirectional reflectance and transmittance distribution functions were inputed as optical parameters of leaves in the canopy radiative model. The canopy radiative model was applied in simulating solar direct radiation distribution in maize canopies. The important contents are listed following:(1) Design a device for measuring scattering flux from leaves in the plane of incidence can be measured within 360° by increment of 1 ° in 4.2 minutes. Illuminating by light source with wavelength of 650 nm and 830 nm, bidirectional reflectance from a white board (taken as reference), and bidirectional scattering (in reflectance and transmittance) from a leaf of evergreen euonymus (Euonymus japonicus Thumb.) were measured separately. Relative standard deviation of repeated measurements of white board and evergreen euonymus leaf were 0.2% and 1.31% respectively.(2) Measure radiant flux distribution in the plane of incidence of a leaf of evergreen euonymus {Euonymus japonicus Thumb.) using a self-designed device, from which analytic bidirectional reflectance and transmittance distribution function models were calibrated with Cook-Torrance and Lambert approach. Validations of the calibrated models showed that the determinative coefficients (R2) of reflectance models at wavelength of 650 nm and 830 nm were 0.95 and 0.91 respectively, and that of transmittance model at wavelength of 830 nm was 0.73.(3) Construct a three dimensional radiation transfer model of plant canopy with Mote Carlo ray tracing. Bidirectional reflectance and transmittance distribution functions were inputed as optical parameter of leaves in simulating the light scattering from leaves. The distribution of light came from solar and scattering from leaves were simulated and outputed separately,(4) Simulate the spatial distribution of direct solar radiation in maize canopy based on the model. The 3D distribution of direct solar radiation in maize canopy was simulated and visualized. Vertical distribution derived from 3D distribution of direct solar radiation was comfirmed by vertical PAR profiles measured on-site.(5) Simulate the three dimensional distribution of radiation scattering from leaves in maize plant canopy. The Results showed that scattering lights at 650 nm were dispersed as highlights in canopy. Scattering lights at 830 nm were distributed more evenly than those of 650 nm.From this study, it is shown that the constructed canopy radiative model can be used to simulate three dimensional distributions of photosynthetic active radiation in plant canopy. It is suggested that thedistribution of radiations scattering from leaves in canopy should be simulated separately at different wave length.