The GPR Forward Modeling of the Karst of Coal Mine

摘要

In recent years, with the increase in depth and the expansion of the scope in coal mining, water inrush accident happens constantly. Firstly, Based on the theory of electromagnetic field and electromagnetic wave, this paper elaborates the numerical calculation method of electromagnetic field, finite-difference time-domain (FDTD), and deduces two-dimensional Finite Difference Time Domain equations according to Maxwell rotation equations in detail. In order to ensure the numerical stability of this algorithm, and to avoid numerical dispersive phenomenon, the relational expression of grid space step and time step is derived. The paper analyzes the respective merit and shortcoming of the two absorbing boundary condition, Mur and PML. Then it focuses on the principle of the PML absorbing boundary condition and gives the grid differential format in PML absorbing layers. Secondly, in order to simulate the karst possibly encountered during mining in karst developed and water-rich mine areas, two-dimensional GPr forward model is established, and the radar profiles are synthesized using FDTD method. It is clear to see the abnormal body's reflected curves and intuitive to understand the karst's characters in the radar profiles, which are helpful to improve the accuracy of interpretation in actual detection.