基于地基激光雷达数据的落叶松人工林削度方程构建

Construction of the taper equation of Larix olgensis plantations based on Terrestrial Laser Scanning data

【目的】探究使用地基激光雷达(Terrestrial Laser Scanning,简称TLS)点云数据提取人工落叶松树干不同相对高处直径的精度,构建落叶松树干削度方程,验证地基激光雷达获取数据的可行性,改变传统的获取森林参数的方式,能够为森林资源规划管理和决策提供技术性支持。【方法】以黑龙江省佳木斯市孟家岗林场8块皆伐样地的落叶松人工林为研究对象,首先借助TLS扫描样地,然后测量伐倒木相对高处直径;并以伐倒木实测值为真值,分析TLS提取的相对高处直径精度,最后采用点云数据提取的直径构建削度方程。选取9个削度方程基础模型,根据评价指标选出最优基础模型,以样木为随机效应建立基于单木水平的混合效应模型。【结果】TLS获取的树干直径数据满足精度要求,且适用于削度方程的构建,其中胸径(R^(2)=0.9939)的提取效果好于树高(R^(2)=0.9139);随着树干高度的增加,相对高处直径R^(2)逐渐增大,到0.06h处直径的提取精度最高(R^(2)=0.9912),随后R^(2)逐渐减小,在0.8h(R^(2)=0.8763)、0.9h处,由于树冠遮挡,获取的树干点云密度较小,导致提取效果较差;使用TLS数据构建的9个削度方程中,Kozak-1988的拟合效果最好(R^(2)=0.9783、RMSE=1.1799);通过比较模型在不同径阶下和不同相对高处的预测能力,分析发现Kozak-1988比Kozak-2004和曾伟生模型更适合描述孟家岗林场落叶松的干形变化,因此Kozak-1988为基于TLS数据构建的最优基础模型;最后采用Kozak-1988构建基于样木水平的三参数混合效应模型精度达到99.77%。【结论】TLS获取的树干相对高处直径数据精度较高,基于点云数据构建的人工落叶松削度方程拟合效果较好,可以为后续出材率表的编制做准备,并为孟家岗林场科学合理的造材提供理论依据。

【Objective】This study was designed to investigate the accuracy of extracting the diameters of Larix olgensis at different relative heights by using Terrestrial Laser Scanning(TLS) point cloud data and construct the Larix taper equation, in order to verify the feasibility of ground-based LIDAR data acquisition and to change the traditional way to obtain forest parameters. The results of the work can provide technical support for forest resource planning, management and decision-making.【Method】In this article,eight Larix olgensis plots from Mengjiagang forestry field in Jiamusi city, Heilongjiang province were scanned with TLS, and then the relative height diameters of felled trees were measured. Nine basic models of the taper equation were selected, and the optimal model was chosen according to the evaluation index. Meanwhile, a mixed-effect model based on the single wood level was established with the sample wood as the random effect.【Result】The trunk diameters obtained by TLS met the accuracy requirement and were suitable for the construction of the taper equation. The extraction effect of diameter at breast height(R^(2)=0.993 9) was better than that of tree height(R^(2)=0.913 9). As the height of the trunk increased, the diameter R^(2) at the relative height gradually increased. The extraction accuracy of the diameter was the highest at 0.06h(R^(2)=0.991 2), and then R^(2) gradually decreased. At 0.8h(R^(2)=0.876 3) and 0.9h, due to the cover of the tree canopy, the density of the obtained trunk point cloud was small, resulting in a poor extraction effect. Among the nine taper equations constructed by using TLS data, Kozak-1988 had the best fitting effect(R^(2)=0.978 3, RMSE =1.179 9). By comparing the prediction ability of the model under different diameters and relative heights, the analysis found that Kozak-1988 was more suitable than Kozak-2004 and Zeng W S model, to describe the trunk shape changes of Larix in Mengjiagang forest farm. Therefore, Kozak-1988was the optimal basic model based on TLS data. Finally, Kozak-1988 was used to construct a three-parameter mixed-effect model based on the level of sample wood, and the accuracy reached 99.77%.【Conclusion】The trunk diameter data obtained by TLS shows high accuracy, and the Larix olgensis taper equation constructed based on the point cloud data has a good fitting effect, which can be used for subsequent compilation of the merchantable volume table, and further provide a scientific basis for the reasonable timber production in Mengjiagang forestry forest farm.