| Full-waveform spaceborne LiDAR ranging is an active remote sensing technology.Due to the strong penetrability of laser pulses,it has unparalleled superiority in estimating forest structure parameters than other forest resource survey methods.For example,the ICESat laser altimetry satellite have achieved certain results in identification of forest type,estimation of tree height and above-ground forest biomass.In order to improve the estimation accuracy of forest structure parameters and high-precision estimation of national and even global carbon storage.Domestic plans to launch a full-waveform spaceborne LiDAR altimetry satellite.The investment and use of this satellite will provide a new kind of data and technical support for national and even global dynamic monitoring of forest resourcesIn order to explore the application potential of domestic spaceborne LiDAR echo waveforms in the estimation of forest structure parameters.First,it is necessary to establish a full-link echo simulation system,select and apply more mature echo waveform data(such as GLAS echo waveform data)to verify the effectiveness of the system.Then,using the echo simulation system,combined with domestic spaceborne LiDAR load parameters and field survey data,simulating domestic spaceborne LiDAR echo waveforms.Finally,based on the domestic spaceborne LiDAR simulation waveforms,identify or estimate the forest types,forest maximum canopy height,and above-ground forest biomass.The main research contents involved as follows:(1)In order to build a three-dimensional model of ground information in the light spot,the finite element principle was introduced,and realized the construction of three-dimensional model of forest trees and terrain.According to the irregular distribution characteristics of the forest terrain in the light spot,combined with the finite element principle,the random terrain was established.and the high-precision three-dimensional modeling of the actual terrain in the forest stand was completed.Considering the affecte of atmospheric scattering,absorption and refraction,the laser pulse radiation transmission model was added to realize the high-precision simulation of spaceborne LiDAR echo waveform.(2)In order to verify the effectiveness of the full-link echo simulation system.GLAS waveform data was selected as verification data,to analyze the correlation of GLAS simulation waveforms.The research results show that the average value of Pearson correlation coefficient between the simulated GLAS emission waveform and the measured one was 0.96;the maximum value of Pearson correlation coefficient between the simulated GLAS echowaveform and the measured echo waveform was 0.95,and the average value was 0.77.The research results show that the echo simulation system established in this study can high-precision simulate the echo waveform of spaceborne lidar,and can be used for the simulation of domestic spaceborne lidar echo waveform.(3)In order to improve the accuracy of forest type identification,this study combined echo simulation principles and forest canopy characteristics to analysis the echo waveforms of domestic spaceborne LiDAR.The waveform characteristic parameters R_cafit1-47 and K1-47 related to forest types were proposed,and combined with other waveform characteristic parameters to establish waveform characteristic parameter combinations to identity forest type.The overall forest type recognition accuracy was 92.86%when the waveform feature parameter combinations of R_coafit1-47,K1-47to identify the forest types of coniferous forests and broad-leaved forests.The overall forest type recognition accuracy was 75.68%when the waveform feature parameter combinations of R_cafit1-47K1-47to identify the forest types of coniferous forest,broad-leaved forest and mixed forest.In the combination of multiple waveform characteristic parameters,R_cafit1-47,K1-47,AGS and SGS parameter combinations have the highest forest type recognition accuracy.The forest type recognition accuracy of coniferous forest and broad-leaved forest was 96.43%,and the recognition accuracy of coniferous forest,broad-leaved forest and mixed forest was 81.08%.The research results show that the domestic spaceborne LiDAR echo waveform has obvious advantages in the recognition of coniferous forest and broad-leaved forest.But the accuracy of forest type recognition in coniferous forest,broad-leaved forest and mixed forest was low.(4)In order to improve the accuracy of the maximum tree height estimation,this study analyzed the echo waveform of the domestic spaceborne LiDAR based on the characteristics of the forest canopy structure.And extract the waveform feature parameters related to the forest canopy height leadcor(corrected waveform leading edge length)and trai1-47-(corrected waveform trailing edge length).And combined with other waveform feature parameters to create tree overestimation models.The research results show that the linear estimation model of forest maximum tree height established under the combination of Wi and TS parameters has the highest modeling accuracy.The maximum forest tree height estimation accuracy of Adj.R2 under the conditions of 0?10°,0?20° and 0?30°.R2 were 0.88,0.83,and 0.73,respectively.The RMSE were 1.04m,1.76m,and 1.62m,respectively.The estimation accuracy of adj.R2 of coniferous forest,broad-leaved forest and mixed forest were 0.79,0.83 and 0.80.And the RMSE were 1.60m,1.07m and 0.92m,respectively.The research results show that the domestic spaceborne LiDAR has obvious advantages in estimating the maximum value of tree height.And the combination of the waveform characteristic parameter W1 and TS can significantly improve the estimation accuracy of maximum tree height.(5)In order to improve the estimation accuracy of the above-ground forest biomass.This study analysised the echo waveform of the domestic spaceborne LiDAR based on the characteristics of the forest canopy structure.And extracted the parameter of canopy echo energy value E related to above-ground forest biomass.This parameter were used to establish a linear estimation model of above-ground forest biomass to estimate above-ground forest biomass under the conditions of different terrain slopes and forest types.The estimation accuracy of the aboveground forest biomass under the conditions of terrain slope of 0-10°,0-20° and 0-30° was 0.94,0.92 and 0.91,respectively.The RMSE was 9.53 thm-2,11.50 t.hm-2 and 13.66 thm-2,respectively.The estimation accuracy of aboveground forest biomass in coniferous forest,broad-leaved forest and mixed forest spot was 0.92,0.96 and 0.93,respectively.The RMSE was 11.26 t.hm-2,5.8 thm-2 and 13.61 t.hm-2,respectively.The research results show that the domestic spaceborne LiDAR echo waveform has a higher advantage in the estimation of the above-ground forest biomass.And the parameter of the canopy echo energy parameter E can realize high-precision estimation of above-ground forest biomass. 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