Health assessment of tree trunk by using acoustic-laser technique and sonic tomography

An innovative tree defect detection scheme, which combines acoustic-laser technique and sonic tomography, is studied. A new sensor distribution can be adopted based on the near-surface response detected by acoustic-laser technique, and a more reliable image of the tree trunk can be observed by sonic tomography. By using such hybrid detection scheme, the near-surface defects (bark detachment, cracks, decay) can be revealed at the early stages of defect development. The accuracy of defect detection during advanced tree risk assessment is therefore highly improved. As a newly developed detection technique for detecting the near-surface defect in tree trunk, the measurement results of acoustic-laser technique in tree trunk are comprehensively discussed, especially toward the detectable depth beneath the tree surface. The experimental results demonstrated that the acoustic-laser technique can identify the presence of near-surface defects in a tree trunk that are normally overlooked by the conventional sonic tomography measurements with random distribution of sensors.