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.

Decay Detection in an Ancient Column with Combined Close-Range Photogrammetry (CRP) and Ultrasonic Tomography

“…In a second stage, the images that were previously quality-checked (carefully selected) by the operator are aligned very precisely using bundle adjustment algorithms as well [41] and a sparce point cloud is generated. In the third step, this cloud is used as input in the computation of the final unstructured unified dense point cloud representing the high resolution 3D-model of the studied body, by means of Multi Video Stereo view (MVS) styled algorithms [3,4,6,9,25].…”

“…As a coupling agent, silicone snug sheets were used. From previous experimental ultrasonic applications [3,4,6,9,25], it was found that this kind of coupling agent is particularly suitable for use in porous media, such as natural materials. It optimises the transmissibility of the ultrasonic signal, filling the irregularities at the interface while avoiding soiling the material and interfering with it.…”

“…Non-destructive techniques are constantly being improved in many fields of the applied sciences, as described by numerous authors [3][4][5][6][7][8][9][10][11][12][13]. For instance, contactless remote and proximal sensing methods can represent an optimal solution for the 3D accurate modelling of architectural elements.…”

“…The quantitative analysis of thermography applied to architectural structures allows an effective diagnosis of the decay of shallow materials, as well as the identification of the possible causes of their weakness [21]. While other techniques, such as the ultrasonic ones based on the analysis of the propagation of ultrasonic signals, inspect inside the materials [3][4][5][6]8,9,[22][23][24][25][26][27][28][29][30]. The ultrasonic velocity distribution is strictly related to the physical condition of the rocks and to many petrophysical characteristics.…”

3D reconstruction of the tree internal decay based on radar waves

“…Zhang and Khoshelham (2020) proposed a reconstruction method by combining structure from motion (SfM) photogrammetry and acoustic tomography to determine the internal wood quality. Puxeddu et al (2021) used close photogrammetry (CPR) and three-dimensional ultrasound to reconstruct the internal decay of a living adult holm oak. These methods can directly show the volume of wood defects and quantitatively understand the three-dimensional distribution of attenuation.…”