Simulation based evaluation of buried utility response

Finite difference time domain (FDTD) method is widely used to understand and interpret results of Ground penetrating radars (GPR). Simulation studies using FDTD on response of buried features to GPR is a standard practice. However, quantification of these simulated GPR response, which is required for application to real life problems, is not common. In the present work, several scenarios of pipe buried in a homogeneous medium is considered under various combinations of medium properties, buried pipe properties and antenna frequencies and corresponding hyperbolas are simulated using GprMax FDTD tool. Response surface method (RSM) is an established mathematical and statistical method to model the output of any experiment influenced by several independent input variables. Using Design Expert as RSM tool, values of axes `a' and `b', extracted from the simulated hyperbolas, are modeled as functions of influencing parameters. Knowing the axes of the hyperbola, one can estimate the size of the buried utility. The models are validated by computing a and b for experiments carried out using a special setup in air medium. Pipes are held at different heights above ground and an upward facing GPR is towed underneath, perpendicular to their lengths. The studies on pipes used 400 MHz antenna and results are presented for Galvanized iron (GI) pipe. The models are also used to compute `a' and `b' for a few actual buried pipes. The results show a good correlation indicating the possibility of predicting utility dimensions through simulation.