Radiosity Based Distribution Simulation Of Photosynthetic Active Radiation Simulation Within Virtual Loquat Orchard Canopy

Photosynthetic Active Radiation(PAR)is the main source of energy for plant's photosynthesis and affecting plant growth,development and productivity.PAR can be divided into direct solar PAR,scattering PAR and canopy multiple scattering PAR,in which direct solar PAR and scattering PAR are the main components of PAR in the canopy.The multiple scattering of total radiation is relatively low,generally distributed in the inner chamber and low canopy position.But leaves within these parts are mostly below the light saturation point,and the increasing of these leaves' PAR significantly raises the photosynthetic rate.In addition,the terrain is the primary carrier of fruit trees.The distribution of terrain reflected light PAR within the canopy also affects photosynthesis.In this paper,the distribution of PAR in orchard canopy was simulated based on the virtual loquat orchard which consists of three-dimensional geometrical models.The main research contents and results are listing as follows:(1)The virtual scene of orchard is composed of fruit trees and three-dimensional terrain.By using the method of inverse distance weighted(IDW),the terrain point data are spatially interpolated to build the terrain grid.Firstly,build the model of loquat leaf line frame using the point cloud data so that the fluctuation of real leaves and the aggregation of leaf clusters are able to be simulated.Secondly,according to the morphological and structural parameters of loquat,build branch system,which is realized by self-developed parameterized single tree modeling software ParaTree.Thirdly,set up the leaf model on the branch system so that the geometric model of loquat tree is constructed.Finally,on the basis of the growing position of each loquat tree,the individual tree model is "planted" on the surface of the terrain,and the virtual loquat orchard is formed by using the instantiation method.(2)The process of simulating the light distribution in an orchard canopy is as below.According to the geographic coordinates and the simulation time of plant tree growth,set the light source information and the initial radiation intensity.Calculate the form factor of radiosity model using 3D-discrete view factor method(3D-DVF)based on the geometrical model of loquat and the geometric information of the light source.Solve the radiosity model so that the direct solar PAR,the scattering PAR and the initial energy of the terrain grid.Then set the terrain grid as part of the light source.and the radiation model is constructed again with the loquat geometry model to calculate the ground reflection PAR in the loquat canopy.Add the PAR value of each surface element to obtain radiation intensity of each surface element in the loquat orchard canopy.(3)As the large amount of light radiation simulation and transmission times in orchard scene,redesign the triangle metadata structure using CUDA Thrust library.Using memory mapping for CPU data reading,and using a virtual unified addressing for GPU data reading,thus optimize the data transfer between CPU and GPU.(4)The distribution of photosynthetically active radiation in the canopy of loquat orchard is simulated with different slope and different slope plots,within 10 different time and different planting densities in one day.The results showed that 16 strains of 12 strains of planting density and planting density of orchard canopy light distribution made only a piece of difference,25 degrees slope based orchard received more light and shady slope orchard canopy light interception was about 65%of sunny orchard canopy.