Abstract
Airborne LiDAR (Light Detection And Ranging) remote sensing for individual tree-level forest inventory necessitates proper extraction of individual trees and accurate measurement of tree structural parameters. Due to the inadequate tree finding capability offered by LiDAR technology and the complex patterns of forest canopies, significant omission and commission errors occur frequently in the segmentation results. Aimed at error reduction and accuracy refinement, this paper presents a novel adaptive mean shift-based clustering scheme aided by a tree trunk detection technique to segment individual trees and estimate tree structural parameters based solely on the airborne LiDAR data. Tree trunks are detected by analyzing points’ vertical histogram to detach all potential crown points and then clustering the separated trunk points according to their horizontal mutual distances. The detected trunk information is used to adaptively calibrate the kernel bandwidth of the mean shift procedure in the fine segmentation stage by applying an original 2D (two-dimensional) estimation of individual crown diameters. Trunk detection results and LiDAR point clusters generated by the adaptive mean shift procedures serve as mutual references for final detection of individual trees. Experimental results show that a combination of adaptive mean shift clustering and detected tree trunk can provide a significant performance improvement in individual tree-level forest measurement. Compared with conventional clustering techniques, the trunk detection-aided mean shift clustering approach can detect 91.1% of the trees (“recall”) with a higher tree positioning accuracy (the mean positioning error is reduced by 33%) in a multi-layered coniferous and broad-leaved mixed forest in South China, and 93.5% of the identified trees are correct (“precision”). The tree detection brings the estimation of structural parameters for individual trees up to an accuracy level: −2.2% mean relative error and 5.8% relative RMSE (Root Mean Square Error) for tree height and 0.6% mean relative error and 21.9% relative RMSE for crown diameter, respectively.
Highlights
As one of the main terrestrial ecosystems, forests play a vital role in the conservation of biological diversity and suppression of climate change
We focus on developing an improved technological scheme using a trunk detection-aided adaptive mean shift algorithm for accuracy refinement to segment individual trees and estimate tree structural parameters based solely on the airborne LiDAR data
The objectives of this study are (i) to highlight a new adaptive mean shift-based clustering approach aided by tree trunk detection using airborne LiDAR data for individual tree detection and tree-based parameter estimation, (ii) to present the results of the proposed approach when applied to small-footprint LiDAR data acquired in a field survey performed in a multi-layered evergreen mixed forest located in South China and (iii) to evaluate the new approach with respect to the tree detection rates and parameter estimation accuracy
Summary
As one of the main terrestrial ecosystems, forests play a vital role in the conservation of biological diversity and suppression of climate change. Large-scale aerial photos or high-spatial resolution remotely-sensed imagery do not directly provide three-dimensional (3D) forest structural information [3]. This limitation can be overcome by a technology called airborne LiDAR (Light Detection And Ranging) [4]. Airborne LiDAR employs state of the art laser technology coupled with high-end GPS (Global Positioning System) and IMU (Inertial Measurement Unit) systems as a means of geo-referencing to produce accurate and detailed scan data from an airborne platform [5]. Due to its ability to generate 3D data with high spatial resolution and accuracy, the airborne LiDAR technology is being increasingly used in remote sensing-based forest resource monitoring [4]
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