Calibration of FDTD Simulation of GPR Signal for Asphalt Pavement Compaction Monitoring

This paper demonstrates that the finite-difference time-domain (FDTD) method can be used to accurately simulate ground-penetrating radar (GPR) wave and its interaction with pavement having different densities and moisture conditions. The FDTD simulation described in this paper is part of the research efforts into the application of GPR on monitoring the density of asphalt pavement during compaction. The challenge is to separate the effect of density increase from the effect of the increase in surface moisture content on GPR signals. The first part of this paper describes the procedure for finding an equivalent excitation function used in simulation that can generate a GPR signal that matches the real signal. Discrete wavelet transform (DWT) was applied to denoise the signal. It was found that the equivalent excitation source and the DWT technique provided an accurate match between the simulation signal and real GPR signal in both the time domain and frequency domain. The second part of this paper demonstrates the application of FDTD simulation in investigating GPR responses on pavements with different densities and surface moisture content. The simulation successfully revealed the “frequency selective” feature of the effect of surface moisture content on GPR signals. Laboratory experiments were also conducted, and the results verified the findings in FDTD simulations. The FDTD simulation was shown to be an effective and efficient tool for studying the interaction of GPR waves with pavement. An accurate modeling of the signal and its propagation provided meaningful insights as well as the possibility for developing practical data-processing techniques.