Method Of Obtaining Direction Distribution Of Canopy Leaves And Spectral Analysis Of Canopy

The study on the radiation scattering characteristics of vegetation canopy is the basis of quantitative remote sensing of multi angle vegetation,which contains abundant vegetation physiological information.By constructing the radiation scattering model of vegetation canopy,remote sensing quantitative inversion of the biophysical parameters of vegetation structure can be realized.However,the irregular geometrical structure of plants leads to the complex optical radiation process.At present,the method of obtaining structural parameters is too dependent on artificial measurement and judgment,and three-dimensional laser scanning can capture the information of point cloud instantaneously and efficiently,so it has a unique advantage in obtaining plant phenotypic characteristics.In this paper,the dense point clouds of four representative plants were collected by hand held laser scanner,and a fast calculation method of leaf inclination distribution was put forward.The accuracy of the simulation is improved by substituting the accurate leaf tilt distribution to the intermediate function of the radiative transfer model.The main research works in this paper are summarized as follows:1.This paper put forward a method based on point cloud to quickly calculate blade direction distribution.By establishing the sampling grid in the spherical space,the coordinates are defined according to the angle of observation and the angle of the leaf.The triangle is searched and constructed,and the probability density function of the leaf direction distribution is calculated by the triangle slice.In order to verify the accuracy of this method,the accuracy of this method is verified by three methods,and the similarity between four different plants is more than 0.9.2.Based on the accurate computation of point cloud modeling,the structural parameters are subdivided into the intermediate functions of the solution,so as to reduce the error of simulation.A new simplified calculation method is proposed.Compared with the classical SAIL model,the error caused by the calculation of extinction coefficient and scattering coefficient is reduced.Through the analysis of two methods of local and global sensitivity,the sensitivity of the SAIL model and the parameters of the simplified model in the model calculation is analyzed,and the significance and value of the improved method are proved.3.To verify the improvement of the method proposed in this paper,the measured spectral data of the four experimental objects are compared with the spectral data simulated by the SAIL model and the spectral data simulated by the improved method in this paper.From the overall similarity,the improved similarity is slightly improved,indicating that the accurate estimation method can effectively improve the precision of the inversion when compared with the traditional ellipsoid estimation method.From the multi angle comparison,the influence of the structural parameters on the spectrum is the most significant in the main direction,the weakest in the main plane,and the other plane in the front.Between the two,the vegetation chlorophyll absorption band,such as blue 450nm and red 670nm,has strong spectral anisotropy,and the influence of structural parameters is particularly prominent,but the near-infrared 860nm weakens the anisotropy of the spectrum because of its high transmission and multiple scattering characteristics,and the improvement degree is not obvious.Through this study,the feasibility of rapid acquisition of plant phenotypic parameters by laser is proved,and the difficult problems in radiation transmission are solved by using accurate structural parameters.