Ground-penetrating radar for tree trunk investigation

Tree trunk inspection is a very important task to predict possible collapses of trees and thus prevent harming people and damages to infrastructure. To perform such investigation non-invasively, ground-penetrating radar (GPR) appears to be a very promising tool. The objective of this paper is to test a frequency-domain radar system with a new home-made transverse electromagnetic (TEM) horn antenna to investigate the internal structure of a laboratory model of a tree trunk. In order to test the horn antenna, a calibration was performed to determine its transfer functions following the intrinsic antenna model of Lambot et al Subsequently, a radar profile was acquired over a sand box to test its imaging capabilities. Finally, a circumferential acquisition around the laboratory model with different antenna-medium distances was performed. Results were compared to a classical time-domain radar acquisition. The new acquired data showed very good GPR profiles, so the horn antenna proved to be a suitable tool for our measurements. In the end, influence of a polar representation of an irregular tree trunk was discussed and the structure from motion (SfM) technique was proposed to acquire a correct shape of an irregular cross section.