Study About Electromagnetic Properties Of GPR Antennas And Objects And Data Interpretation Scheme

The terms subsurface radar or ground penetrating radar refer to a wide range of electromagnetic techniques designed primarily for the detection and location of objects or interfaces buried beneath the earth's surface. It has many advantages such as nondestructive detection, strong penetrability, high resolution ability, operational convenience, low cast, and so on. The transient electromagnetic properties of objects buried in lossy medium, the radiation characteristics of antennas are researched through FDTD method. And the object materials attribute is estimated in the data come from our actual experiments.In chapter 2, the FDTD method and absorbing boundary condition for frequency dependent materials are described in detail. There are two crucial problems on applying this method to the scattering analysis of objects buried in media: 1) to construct the FDTD iterative equations used in dispersive media; 2) to construct the FDTD iterative equations in generalized PML and anisotropic PML, and discuss the performance of them. Then, the propagation characteristics of electromagnetic pulse in the dispersive medium are researched through the method.In chapter 3, the transient scattering characteristics of objects buried in lossy medium are studied when the transmitter and receiver are the simple dipole modal. 1) The mechanism about transient scattering and the factors effecting scattering waveform are analyzed. 2) To compute the scattering field of slider objects, the 2.5D FDTD scheme is applied to the GPML ABC. The scatter characteristic of spindly object, the factors which influence target hyperbola configuration and the horizontal resolution are analyzed by the scheme. 3) The inhomogeneous media model with random fluctuations permittivity and rough surface is generated from a prescribed correlation function. The influence of the random media to the dielectric layer thickness estimation and the detection targets are studied.In chapter 4, the GPR antennas which are one of the most critical hardware components for the performance of the GPR system and their applications are introduced. In the paper, the Bow-tie and TEM horn antenna with distributing resistive loading are present. The radiation waveform, input impedance and near-zone radiation pattern of the antennas are analyzed by FDTD method. It is proved that the time domain response and radiation wave of antennas is improved through appropriate distributing resistively loaded. The manufactured distorted TEM horn with resistive loading has been applied to the GPR system.In chapter 5, the direct wave suppression and objects materials attribute estimation are studied. The clutter can be suppressed from two different schemes which are the method of shielding antennas, placing the layered impendence matching medium between the antennas and ground, and the searching the optimum parameters which is a signal processing method. After suppressing the direct wave, the phase matched method comparing the phase spectrum between target and sample signal is put forward to estimate object materials. The diffraction tomography based on quasi-linear approximation is also applied for the fixed-offset GPR system, and takes into account the planar air-soil interface and evanescent wave. The simulation and experimentation results show that the scheme reduces the error in DT based on linear approximation, and can be adapted for determining the location and properties of the buried objects.