| Terrestrial laser scan(TLS)technology can realize the forest scene rehabilitation through the three-dimensional reconstruction technology,obtain the point cloud data,and realize the accurate non-destructive measurement of forest parameters.The quantification of point cloud distribution information can obtain the characteristic parameters of point cloud,which are related to the point cloud structure and can be used for tree factor inversion.Using TLS to monitor the growth and change of plantations with different planting densities can provide accurate data for plantation management and management,give full play to the economic and ecological efficiency of plantations,and provide references for TLS to be used in broader forestry surveys.Firstly,this research conducted scanning with a multi-echo TLS scanner(Rigel VZ-400i)in the density forest,the calibration experiment was carried out to provide support for field scanning.Then,chose four afforestation densities(6m×6m,5m×5m,3m×8m,4.5m×8m)and three clones(95 poplars,797 poplars,895 poplars,)as the research objects,the scanning experiment was conducted in the research area in 2017 and 2019.And the factors such as tree height,diameter at different heights and volume of the standing trees in two stages were extracted and calculated.The effects of different planting density and clones on the change of poplar tree measurement factors in two periods were analyzed,and the two-period taper equation models were established to analyze the change of taper form,so as to provide reference for plantation management.Finally,using the distribution information of point cloud,designed and extracted the characteristic parameters of the TLS point cloud,namely height cumulative percentage(Hz),analyzed the relationship between it and tree measuration factors,combined with the characteristic parameters of the point clouds in tree height density,established DBH and volume forecast model,analyzed the accuracy and feasibility of laser point cloud characteristic parameters inversion,the main results were as follows:1、Calibration results show that among the three kinds of echoes(full echo,single target echo and first echo)of TLS,the first return had the least noise and the highest diameter accuracy(0.7660 deviation rate).The accuracy of all echo was better.With same scanning sites,the accuracy of diameter measurement through high-density scanning was higher than that of low-density scanning.In practice,it is necessary to encrypt the sites reasonably according to the stand density and select the appropriate echo data according to the tree height for further analysis.2、From 2017 to 2019,the average DBH,height and volume of trees with 6m×6m afforestation density were the largest,while the average DBH,height and volume of trees with 3m×8m afforestation density are the smallest.The DBH growth of trees decreased with the increase of afforestation density,while the height growth of trees increased with the increase of afforestation density.The volume growth of trees decreases with the increase of afforestation density.Afforestation density,clone and the interaction of the two had significant influence on the change of tree height to diameter ratio.The average decrease in the aspect ratio(the absolute value of the change)decreases as the density increases.Among them,the DBH growth of the 95 clones with 6m×6m afforestation density was the best,the height growth of the 895 clones in 5m×5m with afforestation density was the best,and the forest volume growth of the 797 clones in 6m×6m density was the best.The overall performance was that the poplars with high planting density tend to high growth,while the poplars with low planting density tend to radial growth.3、Two stem models with different afforestation densities were established,and the results showed that there were no significant difference in the breast height form factor and breast height form quotient of poplar in the two periods.The relational model of the number and rate of poplar breast height in the two periods was established:f1.3=0.5095q2+1.5208/(q2H).Based on the variable exponential scaling equation d2=Db1+b2H(H-h)b3+b4D/H,the two-phase scaling equation was established,and the stem shape curves of the two phases with different densities were drawn on this basis,which were relatively close,indicating that the trunk shapes of the four afforestation densities in the study period were uniform and kept the same growth.4、The cumulative percentage of height(Hz)was different in different planting density,the mutation can reflect the change of trunk measuration factors in different planting density.The characteristic parameters of point cloud based on TLS have a high correlation with DBH and volume of the stumps,and the correlation between the height cumulative percentage H95 with DBH and volume of the stumps was the highest.By comparing the precision of linear model and nonlinear model,the nonlinear model is more suitable for the inversion of standing parameters of poplar samples in the research area.The characteristic parameters of TLS point cloud can be used to estimation the diameter and volume of standing trees and high accuracy(maximum value of R2 is 0.8873)and good estimation effect in the research area.The accumulative height percentage(Hz)was selected for the independent variables of the estimation model,indicating that Hz plays an important role in the research and construction of the tree factor estimation model. |
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