Abstract
Abstract. In this work, the main focus is on voxel tree modeling using 3-D lidar data for accurate leaf area density (LAD) and woody material volume estimation. For more accurate LAD estimation, the voxel model was constructed by combining airborne and portable ground-based lidar data. The profiles obtained by the two types of lidar complemented each other, thus eliminating blind regions and yielding more accurate LAD profiles than could be obtained by using each type of lidar alone. Parts of the LAD profiles that were underestimated even when data from both lidars were combined were interpolated by using a Gaussian function, yielding improved results. A laser beam coverage index, Ω, incorporating the lidar's laser beam settings and a laser beam attenuation factor, was proposed. This index showed general applicability to explain the LAD estimation error for LAD measurements using different types of lidars. In addition, we proposed a method for accurate woody material volume estimation based on a 3-D voxel-based solid modeling of the tree from portable scanning lidar data. The solid model was composed of consecutive voxels that filled the outer surface and the interior of the stem and large branches. By using the model, the woody material volume of not only the whole target tree but also of any part of the target tree can be directly calculated easily and accurately by counting the number of corresponding voxels and multiplying the result by the per-voxel volume.
Highlights
Trees have important functional roles, including the cycling of materials and energy through photosynthesis and transpiration, the maintenance of microclimates, and the provision of habitats for various species
We propose a method to improve the accuracy of leaf area density (LAD) estimation of a canopy based on 3-D voxel tree modeling by compositing airborne and portable scanning lidar systems
This means that Ω can be used to assess the LAD error of lidar measurements made by using different settings and suggests that Ω, that is, the proportion of the area covered by laser beams in a horizontal plane, is an essential and practical factor that relates to estimation accuracy in lidar-based LAD measurements
Summary
Trees have important functional roles, including the cycling of materials and energy through photosynthesis and transpiration, the maintenance of microclimates, and the provision of habitats for various species. Hosoi and Omasa (2006) recently proposed a voxel-based method of 3-D modeling that uses portable scanning lidar data (Voxel-based Canopy Profiling method) In this method, lidar data points are converted into voxel elements in a 3-D voxel array to faithfully reproduce the canopy as a voxel model. Lidar data points are converted into voxel elements in a 3-D voxel array to faithfully reproduce the canopy as a voxel model This method has been used for estimating vertical leaf area density (LAD) profiles, offering the accurate estimates when sufficient numbers of laser beams were supplied to the canopy. We propose a method to improve the accuracy of LAD estimation of a canopy based on 3-D voxel tree modeling by compositing airborne and portable scanning lidar systems. A method to estimate woody material volume from a lidar-derived 3-D voxel tree model is proposed
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