Multiecho-Recording Mobile Laser Scanning for Enhancing Individual Tree Crown Reconstruction

This paper presents a novel attempt at combining the mobile mapping mode and a multiecho-recording laser scanner, as well as a new methodology based on the resulting single-scan point clouds, for enhancing the integrity of individual tree crown reconstruction. The motive stemmed from the widespread but hard-to-reach demand in precision forestry, i.e., efficiently acquiring the integral 3-D structures of single crowns via single-scan light detection and ranging (LiDAR) surveys. For this task, aerospace and aerial LiDAR is generally subject to low sampling density, and static terrestrial LiDAR is restricted to high relocation cost. As a state-of-the-art mapping technology, mobile laser scanning (MLS) can somehow overcome these limitations owing to its strengths of high sampling density and moving efficiency. However, its laser emissions, even from the incorporated peculiar scanner, still suffer from leaf/branch occlusions. To address this challenge, mirroring the half crowns facing the MLS system to the other sides can be assumed as a solution strategy, in a point of view different from typically strengthening laser transmission penetrability. In the case of no multiscans available, this plan turns out to be unstable due to the shortage of reference data. For this issue, this study further expands the roles of multiechoes beyond penetration, namely, also as the self-indicators for correcting the mirrored half crowns. Quantitative evaluation about the integrity of reconstruction in terms of crown outer surface was conducted based on the sample trees, which were measured by the multiecho-recording MLS and a static terrestrial LiDAR from two opposite sides. The promising results basically validated the proposed technique.