A terrestrial laser scanner-based method for estimating leaf area density (LAD) distribution is examined under considering of the degree of penetration of the laser beams into the tree and the influence of wind, which can lead to errors in outdoor measurements. Two Japanese zelkova (Zelkova serrata) trees, 6m in height, were each scanned from four positions at a distance of 4.5m. To evaluate the influence of wind on the estimation accuracy of the LAD distribution, beam-transparent sheets were installed around one tree to block the wind. LAD distributions with a voxel size of 0.3m×0.3m×0.3m were estimated based on a previously developed method to calculate the contact frequency between laser beams and leaves. Two different methods for analyzing data acquired from multiple scanning positions were examined: calculating LAD from integrated data (integration method), and calculating LAD for each scanning position while adopting maximum LAD for each voxel (selection method). The estimated leaf area was compared with the area measured by stratified clipping. When the wind was blocked, the difference in estimation accuracy between the integration and selection methods was small, even though the number of incident laser beams on each voxel in the selection method was smaller than that in the integration method. The estimation errors in determining the leaf area for the upper, middle, and lower layers of the tree were within 10-15% for both methods. When the wind was not blocked and the wind speed reached 0.5m/s, LAD was overestimated by both methods, but the difference between the LAD estimated with and without shielding was within 10% in the selection method. Conversely, the LAD estimated by the integration method was 20% greater than that estimated by the selection method. These results indicate that the selection method is suitable for estimating LAD distribution in outdoor spaces.
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