基于地基雷达数据构建红松人工林树高、枝下高及接触高模型

Building Tree Height,Height to Crown Base and Crown Contact Height Model for Korean Pine Plantation Based on Terrestrial Laser Scanning Data

采用地面激光雷达(Terrestrial Laser Scanning,TLS)扫描10块人工红松林所得到的数据,与实地调查数据相结合,构建红松树高曲线模型、枝下高预估模型与接触高预估模型,并建立联立方程组。首先,从所选择的5种树高曲线模型中,选择出拟合效果较好的2个模型作为联立方程组的备选模型。然后再从5个枝下高基础模型中选出1个拟合效果好,并且适用程度高的模型作为基础模型,运用再参数化和最优子集回归的方法将林分因子(林分平均胸径、林分断面积、高径比、优势木平均胸径和优势木平均高)代入基础模型,选择拟合效果较好的模型作为枝下高备选模型。相同的方法选择拟合效果好的接触高备选模型。最后将树高曲线模型、枝下高备选模型与接触高备选模型分别两两联立,建立联立方程组。通过似不相关回归(Seemingly Unrelated Regression Estimation,SVR或SURE),根据拟合优度与检验结果选择最优秀的方程组,并对联立方程组进行评价。最终得到结果最优联立方程组预估树高时,决定系数R^(2)=0.896,均方根误差RMSE=0.612 m;当方程组预估枝下高时,R^(2)=0.575,RMSE=0.850 m;当方程预估接触高时,R^(2)=0.719,RMSE=0.791 m,而且各种检验指标都较好。综合来看,方程组对树高、枝下高与接触高拟合精度与检验效果较好,可以解决树高、枝下高与接触高的内在相关性问题,为进一步研究红松树冠结构与动态变化提供基础。

In this paper,data obtained by scanning 10 artificial Korean pine forests based on Terrestrial Laser Scanning(TLS),were combined with field survey data to construct tree height curve model,height to crown base prediction model and crown contact height prediction model,and a simultaneous equation system was established.First,from the five kinds of tree height curve models selected,two models with better fitting effects were selected as the candidate models of the simultaneous equations.Then one model with good fitting effect and high applicability from the five height to crown base models was selected as base model,and the stand factors(mean DBH of stand,stand basal area,ratio of height to diameter,mean DBH of dominant trees and mean height of dominant trees) were introduced into the basic model by means of re-parameterization and optimal subset regression,the model with better fitting effect was selected as the alternative model of height to crown base model.The same method was used to select alternative crown contact height model with good fitting effect.Finally,the tree height curve model,alternative height to crown base model and alternative crown contact height model were combined in pairs to establish simultaneous equations.Through seemingly unrelated regression estimation,the best equations were selected by the goodness of fit and the test results,and the simultaneous equations were evaluated.When the optimal simultaneous equation was used to estimate the tree height,the decision coefficient R^(2) =0.896,and the root mean square error RMSE=0.612 m;when the equations was used to estimate the height to crown,R^(2)=0.575,RMSE=0.850 m;when the equations was used to estimate the crown contact height,R^(2)=0.719,RMSE=0.791 m,and all kinds of inspection indexes were good.On the whole,the equation system had better fitting accuracy and test effect for tree height,height to crown and crown contact height,and can solve the internal correlation problem of tree height,height to crown and crown contact height,which provided the basis for further study of crown structure and dynamic changes of Korean pine.