Estimation of Velocity Distribution in Tree Trunks and Reflection Imaging by GPR Considering Curved Raypaths

Imaging the internal structure of tree trunks by radar is demanded for assessing the health of trees. Living tree trunks usually exhibit velocity distribution and it introduces errors in the reflection imaging when a constant velocity is employed as common imaging methods. The present paper proposes a parametric estimation method of the velocity distribution of electromagnetic waves in tree trunk and ground-penetrating radar (GPR) reflection imaging considering curved raypaths for the accurate imaging of deteriorated are in tree trunk. The method for velocity distribution estimation assumes a linear velocity distribution as a function of the radial position. The commonly used velocity analysis on common mid-point (CMP) measurements is modified to estimate the velocity model from a set of the transmission measurements taking curved raypaths caused by the velocity distribution into account. The method is demonstrated with synthetic data generated by the finite-difference time-domain (FDTD) method. Further, a migration method that considers curved raypaths is proposed and applied to simulated data. The results illustrate that the proposed method images the internal structure of a trunk accurately reflects the size of the deteriorated area, compared to the conventional methods with a constant velocity that may significantly under- or overestimate deteriorated area.