The Research of Ground Penetrating Radar Forward Modeling about Underground Cavity on Beijing Road

Abstract: Ground Penetrating Radar (GPR)is an advanced technique of electromagnetic wave probing working at high frequency with very resolution. Because the electronic waves are characterized by high frequency electromagnetic wave , strongly affected by ground disturbance , complex detecting condition It has some disadvantages in underground hollow detecting as the following: a weak ability of anti-jamming and multiple solutions. Therefore, it will be of great meaning to summarize the road electromagnetic wave propagation in underground hollow, to develop research for underground hollow. It has significant meaning to understand the actual detection of the image and to identify the target body through using GPR forward modeling and studying the propagation of electromagnetic waves.This paper describes the characteristics of GPR signal, research of ground penetrating radar forward modeling. It summarizes the road structural characteristics in Beijing, geophysical characteristics of the material on the surface of road, and the cause of formation of the underground hollows. It develops research of numerical simulating method. The finite-difference scheme and equations are derived for 2-dimensional(TM mode)components Ez, Hx and Hy based on the Maxwell’s Equations. With some special processes for absorbing boundary conditions, source position and conductors,2-D Finite-Difference Time Domain(FDTD)numerical modeling program is developed for GPR survey. It designs six kinds of hollows, realizes the forward simulation of the GPR detecting progress on the underground hollows beneath the road. From ground-penetrating radar reflection amplitude, polarity, velocity, hyperbolic eccentricity angle of the electromagnetic waves, we can study the propagation of electromagnetic waves. The hollow exists below the road, in different environments, empty shape, size, center depth were variable, respectively filling different media conditions, the volume of filling media variables. And select the three empty instances, compare the measured image and the image of the similarities and differences between forward modeling, analysis and causes of the differences exist. Besides,“indicative”anormal patterns in GPR reflected signals for different types of defects are concluded and established. Combining with the practice, it will be refered to by the work of detecting the underground hollow with rada. In the end, this paper summarizes the accomplishment and the existing problems, proposal underground cavity wave propagation characteristics of wall and bottom interface. It suggests that researchers in the establishment of the proposed road underground caves and ground penetrating radar simulation and physical simulation database, contributing to the idea of fast detecting and interpreting the underground hollow…
Key words: Ground Penetration Radar; Cavity; FDTD; Simulation

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