Estimation of average electromagnetic wave velocity in tree trunks for the reflection imaging by GPR

We developed a simple method to estimate average propagation velocity of electromagnetic waves in tree trunks. The method employs GPR transmission measurements that fixes the transmitting antenna and scans receiving antenna circumferentially on the perimeter of a trunk. The data exhibit an arrival time curve since the measurement configuration consists of various propagation lengths. We modified the velocity analysis of CMP measurement and calculate semblance as a function of relative permittivity (or velocity). The maximum semblance indicates the permittivity value that best describes the arrival time curve in the transmission data and the value is the estimation. We demonstrate the method with a laboratory experiment with a drilled log and that the estimated permittivity gives better reflection image than other values.