Simulation and modeling of response of buried pipes using FDTD and RSM

Abstract

Interpretation of B-scans gathered using a GPR is often difficult. The difficulty can be resolved to a large extent if responses of common objects under different scenarios are known. Finite difference time domain (FDTD) simulation is widely used to understand the response of buried objects to GPR under diverse object-ground scenarios. However, relating these responses to discern inherent patterns and trends has not been attempted by many. One useful tool for establishing relations between the responses under diverse conditions is the response surface method (RSM). The study presented here uses RSM along with FDTD simulation of response from buried pipes, modeled as circular air voids in a semi-infinite medium. The GPR response of a pipe is a function of object, host medium, and antenna characteristics. The response of GPR is treated as a RSM 4-parameter 3-level problem requiring 81 simulations; which are obtained from the FDTD method based on the GPRMax v2.0 simulator. The GPR responses considered here are the amplitude at the crown of each hyperbola and axes of each hyperbola (`a' and `b'). The computed amplitudes and hyperbola axes are expressed as functions of influencing parameters. Trend lines are drawn to illustrate the dependence of amplitudes on the parameters varied. The relationships for the axes of the hyperbolas are useful to estimate the size and depth of a pipe. The FDTD simulation combined with RSM helps to understand the response for any scenario falling within the chosen range without further computation-intensive simulations.