Arboriculture & Urban Forestry 45(2): March 2019 57 Figure 2. Calculation of the individual-level crown porosity based on a hemispherical photograph. The two hemicycles framed by the solid lines were integrated and the porosity was calculated. waveforms (by Nakanihon Air Service Co. Ltd., Japan). All of the points obtained had x-, y-, and z-coordinate values and any of following attributes: first, intermediate, last, or only returns. First, inter- mediate, and last refer to the order in which the pro- jected laser hit the tree components while passing through the crown. If all of the energy from a pro- jected laser was returned at the same time, it was recorded as an only return. Data Processing Calculation of Crown Porosity The individual-level crown porosity was calculated based on the hemispherical photographs of each of the 96 trees using CanopOn 2 software (Takenaka 2009), which binarized all the pixels in a hemispheri- cal photograph to classify them as either sky or vege- tation, where the hemispherical photograph was divided into 11 annulus rings split at zenith angles of 8.6°, 16.0°, 24.3°, 32.4°, 40.9°, 49.9°, 57.8°, 65.0°, 73.2°, 81.7°, and 90.0°. Thus, 11 gap fraction values were calculated according to the integrated annuli from 0–8.6° to 0–90.0°. For each of the two photographs per tree, we selected the zenith angle to completely cover the crown on the opposite side from the trunk (Figure 2), with the exception of abnor- mally long branches and overlaps with adjacent trees. The porosity value was calculated by integrating two hemicycles per tree, which we defined as the crown porosity. LiDAR Data Processing A 0.5-m mesh digital elevation model (DEM) was created by building a triangulated irregular network according to the public manual (Geospatial Informa- tion Authority of Japan 2006). For all the LiDAR points, we derived their height above the ground using the DEM data, and the points with height ≥ 1.3 m were classified as ‘‘vegetation’’ points and the remain- ing as ‘‘ground’’ points. The numbers of the “vegeta- tion” points and “ground” points were exported with 0.5-m meshes. The numbers of the points with each return type, i.e., first, intermediate, last, and only returns, were also exported with 0.5-m meshes. The numbers of points in each class and each return type within each crown polygon were calcu- lated. The meshes on the polygon border line were ©2019 International Society of Arboriculture
March 2019
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