Finite-difference time-domain simulation of GPR data

Simulation of digital ground penetrating radar (GPR) wave propagation in two-dimensional media is developed, tested, implemented and applied using a time-domain staggered-grid finitedifference (FD) numerical method. Frequency-dependent attenuation is also incorporated to account for amplitude decay and time shift in the recorded responses. The algorithms are based on an explicit FD solution to Maxwell's curl equations. In addition, the first-order TE mode responses of wave propagation phenomena are considered due to the operating frequency of current GPR instruments. The staggered grid technique is used to sample the field and approximated by an explicit second-order difference time marching scheme. By combining paraxial approximation of the one-way equation (Az) and the damping mechanism (sponge filter), we propose a new composite absorbing boundary conditions (ABC) algorithm that effectively absorbs both incoming and outgoing waves. To overcome the angle and frequency-dependent characteristic of the absorbing behaviors, each ABC has two types of absorption mechanism. By applying any combination of absorbing mechanism, non-physical reflections from the computation domain boundary can be effectively minimized. The algorithm enables us to use very thin absorbing boundaries. The model can be parameterized through velocity, relative electrical permitivity (dielectric constant), electrical conductivity, magnetic permeability, loss tangent, Q values and attenuation. According to this scheme, widely varying electrical properties of near-surface earth materials can be modeled. The capability of simulating common-source, constant offset and zero-offset gathers is also demonstrated through various synthetic examples. The algorithms are also applied to iterative modeling of GPR data acquired over a gymnasium construction site on the NCCU campus.