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    机载LiDAR在红树林林分平均高估算中的应用

    Application of airborne LiDAR in the estimation of the mean height of mangrove stand

    • 摘要: 构建基于激光雷达(light detection and ranging,LiDAR)数据的林分平均高反演模型可为无瓣海桑长势的动态监测提供技术支撑。以北部湾茅尾海无瓣海桑红树林湿地为对象,基于机载LiDAR提取的高度和强度参数变量,借助决定系数R2、均方根误差RMSE、赤池信息准则AIC和贝叶斯信息准则BIC指标对随机森林、支持向量机以及神经网络3种模型进行了优选,在最优模型的支持下估算了研究区的红树林平均高及其空间分布状况。结果表明,研究区无瓣海桑的林分平均高介于3.90~11.58 m之间,其中树高较高、胸径较大的无瓣海桑主要分布在潮沟附近以及研究区中部。在估算无瓣海桑的林分平均高时,贡献率最大的是样方点云高度最大值,其次是75%~99%分位数高度。随机森林回归模型在估测林分平均高模型中的精度最高(R2=0.938 1,RMSE=0.58 m,AIC=80.50和BIC=49.05); 支持向量机模型次之,该模型在测试阶段的R2为0.766 5,RMSE为1.27 m; 神经网络模型的拟合效果最差。总体而言,随机森林模型是研究区无瓣海桑林分平均高反演的最优模型。

       

      Abstract: This study constructed a stand mean height inversion model based on LiDAR data, aiming to provide dynamic monitoring of the growth of Sonneratia apetala. Taking the mangrove wetland of Sonneratia apetala in the Maowei Sea of Beibu Gulf as the study object and based on the height and intensity parameters extracted using airborne LiDAR data, this study compared three models, namely random forest, support vector machine, and neural network, based on the coefficient of determination (R2), root mean square error (RMSE), Akachi information criterion (AIC), and Bayesian information criterion (BIC) and then estimated the mean height and spatial distribution of Mangrove in the study area using the optimal model. The results are as follows. The stand mean height of Sonneratia apetala in the study area is 3.90~11.58 m, and Sonneratia apetala with a higher tree height and a larger diameter at breast height is mainly distributed near the tidal trench and the middle part of the study area. In the estimation of the stand mean height of Sonneratia apetala, the maximum percentile height (hmax) had the highest contribution rate, followed by 75%~99% percentile height. The random forest regression model yielded the highest precision (R2=0.938 1,RMSE=0.58 m,AIC=80.50, and BIC=49.05), followed by the support vector machine model (R2 = 0.766 5 and RMSE = 1.27 m in the test stage), and the neural network regression model yielded the worst fitting effects. Overall, the random forest model is the optimal model for the inversion of the stand mean height of Sonneratia apetala in the study area.

       

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