Abstract The finite-difference time-domain (FDTD) method for the simulation of transient electromagnetic (TEM) fields typically applies an upward-continuation boundary condition on the earth-air interface to avoid time-stepping of the field in air, which is not suitable for the modeling of topography and comprises limited parallel efficiency. We present a finite-difference time-domain algorithm based on a segmented solution for 3D TEM modeling with grounded-wire sources, which includes the air layer in the computational domain capable of modeling rugged topography and allows for larger time steps at late times to reduce the computation time. By utilizing the same time-stepping equations within the air layer as that in the earth, this scheme achieves high parallelism, making it easily accelerated by a Graphics Processing Unit (GPU) to improve computational efficiency. To ensure stability in time-stepping the electromagnetic field in air, a Gaussian function was used to convolve the transmitting waveform, thereby eliminating the high-frequency components above the frequency range of the TEM systems. A segmented solution approach was adopted, enabling separate computations for the early- and late-time electromagnetic fields. In the late stage, the air conductivity was treated as a higher value, allowing larger time steps without compromising the accuracy, thus improving the computational efficiency. Tests were conducted using a homogeneous half-space, layered, and 3D complex models demonstrating the computational efficiency, accuracy, and reliability of the algorithm. Additionally, the results from the topography and land-sea model simulations further confirm that this algorithm can be effectively applied to the modeling of rugged terrain and complex geological structures.
Chang et al. (Sun,) studied this question.
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