3D Imaging of CRP and Ultrasonic Tomography to Detect Decay in a Living Adult Holm Oak (Quercus ilex L.) in Sardinia (Italy)

Abstract

A field-integrated methodology using 3D ultrasonic tomography supported by close range photogrammetry (CRP) has been developed and evaluated as a tool to detect the presence and patterns of decay forms in a living adult holm oak (Quercus ilex L.) in an urban green area of the city of Cagliari, Sardinia, Italy. Close range photogrammetry was used to compute a high resolution 3D model of the studied tree, texturized with natural colors. Moreover, following the implemented workflow process it was possible to evaluate the deformation pattern of the studied tree over time. In a second step of our integrated approach, and in order to diagnose the state of health of the inner part of the studied tree in a non-invasive way, laboratory and in situ non-invasive ultrasonic techniques were applied. The results of the close range photogrammetry analysis supported the optimal design of the 3D ultrasonic tomography of the living adult holm oak. Ultrasonic tomography is one of the most powerful non-destructive testing techniques for the full-volume inspection of a structure. It produced physical information on the inner structure of the stem of the investigated tree. The results of the study show that the integrated application of close range photogrammetry and 3D ultrasonic tomography is a powerful tool for a highly accurate and objective evaluation of the external and internal decay of trees and for monitoring their conservation states. With the fully integrated approach, the diagnostic process aimed to prevent instability and the failure of trees can be greatly improved.