Automatic segmentation of acoustic tomography images for the measurement of wood decay

Abstract

In the assessment of standing trees, an acoustic tomographic device is a valuable tool as it permits to acquire data from the inner part of the trees without causing them to fall down unnecessarily. The interpretation of the images produced by these devices is part of the diagnosis process for urban trees management. This paper presents a segmentation methodology to identify defective regions in cross-section tomographic images obtained with an Arbotom® device. Two trunk samples obtained from a Blackwood Acacia tree (Acacia melanoxylon) were tested, simulating defects by drilling holes with known geometry, size and position and using different numbers of sensors. Tomograms from the trunk cross sections were processed to align the propagation velocity data with the corresponding region, either healthy or defective. The segmentation methodology proposed aims to find a velocity threshold value to separate the defective region adjusting a logistic regression model to obtain the value that maximizes a performance criterion, using in this case the geometric mean. Two criteria were used to validate this methodology: the geometric mean and the surface ratio detected. Although an optimal threshold value was found for each experiment, this value was strongly influenced by the defect characteristics and the number of sensors. The correctly segmented area ranging from 54 to 93% demonstrates that the threshold method is not always the most proper way to process this type of images, and thereby further research is required in image processing and analysis. (Résumé d'auteur

Sustainable Management of Very Large Trees with the Use of Acoustic Tomography

“…This is a well-established tool for the assessment of a tree's structural soundness, with numerous studies over the past 20 years testing its application under various conditions. Many research teams have confirmed the effectiveness of acoustic tomography in detecting tree decay [43][44][45][46][47][48][49][50]. At the beginning of the 21st century, research was conducted on the health condition of urban trees using various research methods (electrical and acoustic tomography and GPR), achieving various degrees of success with them.…”

Ultrasound computed tomography on standing trees: accounting for wood anisotropy permits a more accurate detection of defects

“…The images for the defective cases were segmented using a threshold. It has been previously shown that using a threshold value to separate healthy and defective regions is not always the most suitable way of interpreting tomograms (Espinosa et al 2017). In this specific case, the thresholding segmentation was chosen because it allowed comparing quantitatively the two image reconstruction methods.…”

Comparison of variability in results of acoustic tomographs in pedunculate oak (Quercus robur L.)

“…In addition to identification of decay, Alves et al (2015) showed the importance of AT in determining elastic constants of Muiracatiara Brazilian wood (Astronium lecointei). Recently, different image reconstruction methods have been developed and presented (Espinosa et al 2017;Du et al 2018). According to the reliable representation of cavities and degraded wood, AT can be used to predict the loss of load-bearing capacity for trees with internal defects (Burcham et al 2019).…”