Reflection waveforms occurring in GPR tree trunk testing

In order to predict the collapse of a tree, it is necessary to investigate its internal parts. To perform such investigation without harming the tree, ground penetrating radar (GPR) appears to be a promising non-invasive technique. The objective of this study is the investigation of particular features occurring in tree trunk radar images, due to the circumferential data acquisition. This study is also focused on detailed description of electromagnetic wave scattering within the cylindrical object and particular reflection curves. In that respect, two experiments, including a circular medium with a circular hole inside, were performed: (1) numerical simulations, and (2) measurements over a laboratory model. For improving readability of the GPR images, we considered (1) common zero-offset reflection imaging, (2) reflection imaging including a planar perfect electrical conductor (PEC), and (3) reflection imaging including a PEC arc. Besides straight-ray propagation, also total internal reflections (TIR) of waves within the trunk were observed. The analytical expression of the reflection curves was derived for both wave propagation modes. We confirmed our assumptions with a comparison of both experiments and analytical equations.