Research On Hyperspectral Inversion Mechanism And Model Of Chlorophyll In Curly Leaves Based On PROSPECT-MART

Plant optical radiative transfer model is one of the basic models in the field of vegetation remote sensing.It establishes the relationship between vegetation spectrum,biochemical components and vegetation structure parameters.It can monitor the physiological and ecological characteristics of vegetation by quantitatively retrieving the content of pigment in leaves.Compared with the traditional field sampling analysis,it has great advantages in real-time,high efficiency,universality and non-destructive.The traditional vegetation radiative transfer model has a fixed light source angle and a single vertical observation angle.The accuracy of spectral inversion is low and the application scenario is limited.The Vegetation Spectrum of multi angle remote sensing contains a large amount of structural characteristic information of the observed vegetation,which has better potential in solving vegetation characteristic parameters such as vegetation pigment inversion.The traditional radiative transfer model believes that the leaf is a whole plane,but in the actual scene,the leaf will have a certain degree of curl due to the change of light,temperature,water and heat.This curl characteristic will significantly change the multi angle spectrum of the leaf and affect the subsequent pigment inversion.In addition,at present,there is no device that can quantitatively control the spatial state of leaves in the link of spectral data acquisition,so the effectiveness and unity of leaf spectral data are difficult to be guaranteed.In view of the above problems,this study developed a multi angle spectrum measurement device for leaves,which provides the basis for multi angle research of leaves,and explores the multi angle spectrum of flat leaves and curled leaves.Based on the traditional blade radiative transfer model prospect,the multi angle radiative transfer model prospect-ma model of flat blade is constructed.The three-dimensional spatial structure model of leaves is constructed,and the multi angle radiation transfer model of curled leaves is constructed by combining prospect-ma model and ray tracing algorithm.The prospect-mart model provides the basis for the subsequent remote sensing application of canopy scale.The main contents and experiments of this paper include:（1）Development of multi angle spectrum measuring device for leaves and Study on spectral characteristics of curled leaves.A multi angle spectrum measuring device which can quantitatively control the spatial state of blade（blade flattening degree and blade direction）is developed.The spectral measurement results under different blade flattening degree and blade direction were compared and analyzed by variance.Under the two conditions,P was less than 0.05,and there was significant difference.The multi angle spectra of flat and curled leaves at 15°,30°,40°and 55°light source zenith angles at 780nm and 1700nm were analyzed and compared.When the light source zenith angle was 30°and 40°,the spectral distribution of curled leaves showed the characteristics of double hot spots,and there were significant differences in multi angle spectral hot spot distribution and reflectivity between flat and curled leaves.（2）The multi angle radiation transfer model prospect-ma of flat blade is constructed.The light radiation transmission process inside the blade of prospect model is analyzed.Based on prospect model and BRDF model,the radiation transmission process inside the blade is reconstructed,and the multi angle radiation transmission model of the blade with arbitrary light source direction and observation direction is constructed.Prospect-ma model.Use ANGERS database to obtain 500nm-800nm model parameters （?） and K_chls。The model accuracy was verified by prospect-ma for the separation and verification of mirror components of leaf reflection spectrum and the inversion of model pigment.The specular reflection components of 500-800nm band at the incident zenith angle of 15°,the incident azimuth angle of 180°,the observation zenith angle of 45°,the observation azimuth angle of 300°,315°,45°and 60°are simulated and calculated.Compared with the measured values,the RMSes at the four observation angles are 0.0149,0.0102,0.0085 and 0.0089 respectively.The pigment inversion is carried out at 127 observation angles in the hemispheric direction when the azimuth angle of the light source is 180°and the zenith angle of the light source is 15°,30°,40°and 55°.The mean RMSE of the four light source zenith angles is 12.99μg/cm²、14.88μg/cm²、12.37μg/cm²、14.14μg/cm² respectively,the overall average RMSE is 13.60μg/cm².From the hemispherical angle,the RMSE in the mirror direction is slightly larger than that in the non mirror direction.（3）The multi angle radiation transfer model prospect-mart of curled blade is constructed.Using the large deflection static balance theory,the curl dynamic balance relationship of curled blade is established,and the nonlinear differential equation of curled blade along the main pulse direction is constructed.Through the first-order approximate differential treatment and parabolic approximate treatment,the curve of curled blade in the main pulse direction is modeled as a standard parabolic equation.The vertical main vein side of curly blade is approximately modeled as ellipse.The curl degree a of curled leaves ranges from 0.0168 to 0.0462,with an average value of 0.264,and the determination coefficient R2 is between 0.8458 and 0.9645,with an average value of 0.9226.The RMSE evaluation function value range of root mean square error is 0.3135mm to 1.0896mm,and the average value is 0.7083mm.The determination coefficient R2 of curl blade boundary function fitting is between 0.981 and 1,and the average value is 0.9972.The RMSE evaluation function of root mean square error ranges from 0.3386 mm to 2.2127 mm,and the average value is 1.0131 mm.Combining the flat blade multi angle radiative transfer model prospect-ma and ray tracing algorithm,the curled blade radiative transfer model prospect-mart is constructed.Compare the measured and simulated values of BRDF at 670nm and 780nm,and the measured and simulated values of leaf spectrum at different angles.In the 670 nm band,the RMSE is 0.0079,0.0065,0.0041,0.003 and the average RMSE is 0.0053 when the zenith angle of the light source is 15°,30°,40°and 55°;In 780nm band,the RMSE is 0.0203,0.0158,0.0182,0.0224 and the average RMSE is 0.0192 when the zenith angle of the light source is 15°,30°,40°and 55°.The pigment retrieval of 46 leaves was carried out in the 500-800 nm band,and the multi angle chlorophyll retrieval effects were compared.The mean RMSE of pigment inversion for zenith angles of 15°,30°,40°and 55°light sources are 15.97μg/cm²、16.87μg/cm²、16.65μg/cm²、19.21μg/cm² respectively,the overall average RMSE is 17.17μg/cm².