Stress wave velocity patterns in the longitudinal-radial plane of trees for defect diagnosis

Acoustic tomography for urban tree inspection typically uses stress wave data to reconstruct tomographic images for the trunk cross section using interpolation algorithm. This traditional technique does not take into account the stress wave velocity patterns along tree height. In this study, we proposed an analytical model for the wave velocity in the longitudinal-radial (LR) plane of a live tree. Both field and laboratory stress wave testing were conducted to determine the stress wave velocity patterns in healthy and defective trees. The results showed that the ratio of the wave velocity at a propagation path angle θ (with respect to the radial direction) to the radial velocity in healthy trees approximated a second-order parabolic curve with respect to the symmetric axis (θ = 0). Our analysis of the velocity patterns indicated that the measured velocities in healthy trees were in a good agreement with the theoretical models. The results of this preliminary study indicated that the stress wave velocity patterns can be used to diagnosis internal defects in urban trees and improve the accuracy of 3D tomographic images in tree inspection applications.