“…At present, the forward modeling methods of GPR mainly include the finite element method (FEM) [16,17], ray tracing method [18,19], the pseudo-spectral time domain method (PSTD) [20], the fast multipole method [21], the finite difference time domain method (FDTD) [22][23][24], the alternating direction-implicit FDTD (ADI-FDTD) [25], and the symplectic Euler algorithm [26,27]. Although these methods can accurately simulate the propagation of a GPR electromagnetic wave in underground structures, these algorithms have some shortcomings with respect to efficiency and precision.…”