Literature review of acoustic and ultrasonic tomography in standing trees

Abstract

Key message High-resolution imaging is possible if high-frequency sensors are used together with a signalprocessing and inversion algorithm that is well suited to a low signal-to-noise ratio and the effect of wood anisotropy. Wood is a biological growth medium, and given that standing trees adapt themselves in their growth to environmental conditions, their material properties vary with age. These changes result in variations that are far more complex than anisotropy. Wood quality and intraspecific variability can thus be studied to gain an understanding of the development mechanisms of trees, and this can be useful for clonal selection and the management of tree communities. A number of techniques are available to determine wood properties in standing trees, but the signal-processing approaches currently used are not always robust and do not always provide the image resolution needed in the particular cases of acoustic or ultrasonic tomography. This review paper thus aims to present important aspects that should be taken into account when using tomography techniques and addresses a number of open problems. A brief review of current non-destructive wood imaging techniques is initially presented followed by a comparison of the protocols, methods and models used in acoustic and ultrasonic tomography. The devices cited were studied in terms of measurement systems and signal processing. The analysis aimed to highlight and analyze the advantages and disadvantages of each device and describe challenges and trends. The effect of various parameters is discussed: frequency, signal-to-noise ratio, number of sensors and inversion algorithm. General conclusions are then drawn in relation to future signal-processing work in the acoustic and ultrasonic tomography of standing trees. (Résumé d'auteur

Relative roles of termites and saprotrophic microbes as drivers of wood decay: A wood block test

“…Possible approaches include utilizing non (or limited) destructive survey methods such as electrical resistivity (Al Hagrey ; Arciniegas et al . ) or sonic tomography (Gilbert et al . ).…”

Ultrasonic imaging of standing trees: factors influencing the decay detection

“…Several factors influence the quality of the acoustic and ultrasonic images [10]. The number of sensors, for example, is directly related to the spatial resolution of the image; a larger number of sensors allows a smaller defective area detection [11,12].…”

Effects of Convection and Microwave Drying Schemes on the Characteristics and Sound Absorption of Acoustic Oil Palm Boards

“…In the context of the acoustical tomography imaging of standing trees, the wave velocity values are determined for each local area (pixel of the resulting map) of the scanned cross section by solving an ill-conditioned inverse problem with a low number of acoustic measurements (Arciniegas et al 2014). This problem is solved assuming that the transverse cross section of trees is quasi-isotropic.…”

“…This problem is solved assuming that the transverse cross section of trees is quasi-isotropic. The hypothesis of isotropy blurs the image and makes it difficult to characterize the mechanical state of wood and the presence of a defect (Arciniegas et al 2014;Espinosa et al 2017). A way to overcome this problem is to consider the cross section of a standing tree as being cylindrically orthotropic in the process of inversion, such that the 4 elastic constants of wood for each pixel in the radialtangential plane could be determined.…”