Abstract: [Objective] In order to provide a theoretical basis for the analysis, localization and distribution characterization of internal structure and defects of the radar waves by non-destructive testing technique,tree radar tomography were applied to detect internal defects of wood body, and the recognition algorithm of internal reflection features of radar trees was studied and analyzed. [Method] Tomography of Willow wood was carried out with a 900 MHz medium-coupled tree radar. The threshold value, matched filter and Hilbert's algorithm were used to obtain the reflection position of the defect layer. Based on the layer stripping inversion method, the inversion of the dielectric constant were applied for the different media in the tree,and the relative depth of the horizon were calculated,then the point cloud data of the contour of the tree obtained by the 3D laser scanner were mapped, and the absolute position of the B-scan radar image and the contour of the fault were mapped according to the contour tracing method. Therefore, the accurate positioning and characterization of the internal defects of trees were achieved. The three algorithms were respectively verified by finite difference-time-domain (FDTD) forward method, and the method is applied to the test of the ancient willow wood specimen in the Summer Palace.[Result] The results of forward comparison test show that Hilbert plot method is better than threshold method and matched filter method in identifying defects in wood body. The actual willow test results show that the depth error of defects in trees is 10%. The area error of defects calculated by 3D laser and contour scanning technology is about 5%.[Conclusion] The method proposed in this paper can realize the accurate localization and imaging distribution of the internal defects of the trees by the radar wave scanning images.

Key words: radar wave, laser scanning, threshold, match filter, Hilbert, locate abnormal