基于无人机激光雷达的天然林林隙识别

Forest gap identification in natural forest based on UAV LiDAR

【目的】自然干扰引起的森林冠层林隙是天然林更新动态的主要驱动力,林隙的分布、形状和范围可以影响光照和土壤水分等生态因子。林隙的识别和特征描述对于理解森林的动态变化有着重要的意义。【方法】以云南省普洱太阳河保护区无人机飞行区域为研究区,根据无人机激光雷达点云数据提取冠层高度模型;然后使用固定阈值法、相对高度阈值法和面向对象分类法对冠层高度模型数据进行林隙识别,通过图像目视解释获得独立验证样本进行精度评估;最后精度选取最优方法提取的林隙描述其空间特征。【结果】固定阈值法的总体精度为92.00%,高于相对高度阈值法(66.00%)和面向对象分类法(88.00%)。研究区内林隙主要以中小林隙为主,干扰事件较少;研究区林隙的形状指数均值为1.97,多为形状指数较小、边缘效应不太明显的林隙,并且林隙的空间分布为聚集分布。【结论】利用无人机激光雷达数据和固定阈值法可以准确绘制出小范围亚热带天然林的林隙空间分布特征。

[Objective] The forest gaps caused by natural disturbance are the main driving force of the natural forest regeneration and the distribution, shape and extent of forest gaps can affect a series of ecological factors, such as sun light and soil moisture. The identification and characterization of forest gaps are of significance for understanding the dynamic changes of forests. [Method] The remote sensing of UAV can quickly obtain the three-dimensional spatial information of the forest. The study site is located in the UAV flight coverage at the Puer Sun River Reserve in Yunnan Province of southwestern China. The canopy height model(CHM) was derived from the point cloud data of UAV LiDAR. The fixed threshold method, relative height threshold method and object-oriented classification were used to identify forest gaps in CHM. The reference data from visual interpretation of images were used for accuracy assessment of forest gap identification. Finally, the best method was selected to describe the spatial characteristics of forest gaps.[Result] The experimental result showed that the overall accuracy of the fixed threshold method was92.00%, which was higher than the relative height threshold method(66.00%) and object-oriented classification method(88.00%). The forest gaps in the study site area were mainly small and medium gaps,showing that there were fewer disturbance events. The average shape index of forest gaps in the study site was 1.97 and most of them with small shape index and less obvious edge effect. The spatial distribution of the gap was aggregation. [Conclusion] The spatial distribution of forest gaps and its spatial characteristics in small-scale subtropical natural forests can be mapped by UAV LiDAR data and the fixed threshold method.