Abstract
The outer contours of living trees are often considered as a standard circle during non-destructive testing (NDT) of internal defects using ground-penetrating radar (GPR). However, the detection of classical cross-sections (circular) lacks consideration of irregular contours, making it difficult to accurately locate the radar image of the target. In this paper, we propose a method based on the image affine transformation and the Riemann mapping principle to analyze the effect of irregular detection routes on the geometric characteristics of target reflection hyperbola. First, for the similar output phenomenon in the “hyperbola fitting”, geometric analysis and numerical simulation were performed. Then, the conversion of irregular trunk radar images and physical domain radar images was implemented using the method of image affine transformation and the Riemann mapping principle. Finally, the influence of irregular detection routes on the geometry of the target reflection curve was investigated in detail through numerical simulations and actual experiments. The numerical simulation and measurement results demonstrated that the method in this study could better reflect the imaging characteristics of the target reflection hyperbola under the irregular detection pattern. This method provides assistance to further study the defects of irregular living trees and prevents the misjudgment of targets as a result of hyperbolic distortion, resulting in a greater prospect of application.
Highlights
Living trees, which are precious forestry resources and valuable cultural heritage, are decayed and collapsed due to years of external aggression, causing serious casualties and irreversible cultural losses
Ježová et al [11] investigated the properties of radar images of tree trunks using perimeter data as a geometric cross-section of the trunk and illustrated the total internal reflection (TIR) phenomenon
Wen et al [12] proposed a method to locate the internal defects of living trees, combining the relative position with the point cloud data of the external contour of the trees, and designed software for the analysis of the internal structure of living trees based on radar waves
Summary
Living trees, which are precious forestry resources and valuable cultural heritage, are decayed and collapsed due to years of external aggression, causing serious casualties and irreversible cultural losses. To avoid damage to valuable trees, non-invasive methods are used to detect early defects, as they generally occur in the center of the wood and cannot be accurately monitored and measured from the outside [1]. In the health assessment of defects in the internal part of the tree trunk. Wen et al [12] proposed a method to locate the internal defects of living trees, combining the relative position with the point cloud data of the external contour of the trees, and designed software for the analysis of the internal structure of living trees based on radar waves. The vast majority of trees in nature are irregular cylinders. To address this phenomenon, Giannakis et al [13] proposed a scheme for the detection of internal targets by GPR along irregularly shaped closed curves. It was found that the radar reflection curve of the targets was not a typical hyperbolic curve but a very complex shape
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