【摘要】 森林冠层体密度CBD (Canopy Bulk Density)和冠层基高CBH (Canopy Base Height)是许多火行为模型的关键输入参数。然而，在中国很少有研究关注这些参数的估算以及在区域的空间分布情况。无人机技术的发展为精细尺度估算CBD和CBH的空间分布提供了机遇。本研究首先利用野外调查数据计算样地的CBD和CBH；然后，利用无人机LiDAR点云和多光谱影像，构建基于面状区域的最优子集和随机森林估算模型，并对估算结果进行评价；最后，绘制研究区的CBD和CBH空间分布图。研究结果表明：采用相同数据源和模型时，估算CBH的R~2总是高于CBD。CBD最优估算方法为融合LiDAR和多光谱数据的随机森林模型，R~2为0.5142,RMSE为0.0773 kg/m~3,rRMSE为40.73%。CBH的最优估算方法为仅使用LiDAR数据的随机森林模型，R~2为0.6477,RMSE为1.6245 m,rRMSE为31.17%。使用单一数据源时，LiDAR估算精度明显高于多光谱数据。融合两种数据源不一定提升CBD和CBH的估算精度。本研究中构建的最优子集模型需要3—6个特征变量，随机森林模型则需要输入10—52个特征变量。仅使用多光谱影像估算CBD和CBH时，最优子集回归估算精度更好，但是空间预测结果易受地表覆盖类型的影响。本研究能够为森林冠层可燃物参数估算提供方法参考，同时也可以为林火行为预测模型提供精细尺度的输入数据。更多还原

【Abstract】 Wildfire behavior modeling programs require spatial layers of Canopy Bulk Density(CBD) and Canopy Base Height(CBH) to predict fire spread. However, the two canopy fuel metrics have been investigated by only a few studies in China. Inaccurate spatial estimates may result from the utilization of traditional field-based estimates, which assume averages across spatial extents. Recently, unmanned aerial vehicles(UAVs) have emerged as valuable tools that provide LiDAR point clouds and multispectral images for estimating CBD and CBH at fine resolution. The main objective of this study is to develop an area-based approach to estimate CBD and CBH and evaluate the accuracy of various UAV datasets at 10 m resolution at the local scale in China. A case study area is set up in Jiaohe City, Jilin Province, which is predominantly covered by coniferous forests in low mountains and hills. Field data, species, crown base height, total tree height, and diameter at breast height are obtained from 106 circular plots and served as modeling and validation datasets. The Fire and Fuels Extension of Forest Vegetation Simulator is used to calculate CBD and CBH for each plot. Best subset regression and random forest models are employed to establish relationships between the 106 field data points collected and the predictive variables derived from UAV LiDAR and multispectral imagery. Given the nonlinearity of the data, the Box – Cox procedure is utilized and shows that 0.5 power transformation is appropriate for best subset regression. The R~2 value of CBD is always lower than that of CBH when the same models and input dataset are used. The fusion of LiDAR with multispectral imagery produces the best accurate estimation of CBD when random forest is employed(R~2 = 0.5142, root mean squared error [RMSE] = 0.0773 kg/m~3, relative RMSE [r RMSE] = 40.73%). LiDAR achieves the most accurate estimation for CBH(R~2 = 0.6477, RMSE = 1.6245 m, rRMSE = 31.17%). For the best subset regression and random forest models, the use of LiDAR point clouds alone has higher accuracy in estimating CBD and CBH compared with the use of multispectral imagery. The best subset regression models have R2 values that are greater than those of the random forest models for multispectral imagery alone. This finding indicates that the CBD and CBH values estimated using multispectral imagery are higher than those estimated using LiDAR at a margin of the study area because of crop land. For the various models, fusing LiDAR with multispectral imagery does not necessarily improve estimation accuracy compared with using LiDAR and multispectral imagery alone. Therefore, we recommend using the random forest model that fuses LiDAR and multispectral imagery and LiDAR alone to map CBD and CBH in the study area, respectively, because they have the lowest RMSE. The best subset regression model involves 3 to 6 variables, and the random forest models have 10 to 52 predictive variables. Among the original LiDAR predictor variables, height features are the most important, and structure features have considerable importance. The selected multispectral imagery features of both models exhibit diversity in various canopy flue metrics. This study provides clear evidence that UAV LiDAR and multispectral imagery can be used to derive fine-resolution CBD and CBH, which are crucial for fire behavior modeling at the landscape scale and for forest management activities and decision-making.更多还原