Forward Modeling And Full Waveform Inversion Imaging Of Ground Penetrating Radar

Ground penetrating radar(GPR)electromagnetic wave detection technology has made great development in recent decades,and its application scope is becoming more and more extensive.In this paper,two problems of GPR forward simulation and full waveform inversion imaging are introduced based on the problem of GPR electromagnetic wave detection.In this paper,Maxwell's equations and FDTD combined with the principle of perfectly matched layer absorption boundary conditions are used to study the forward numerical simulation of two-dimensional electromagnetic wave detection in GPR.Full waveform inversion method is applied to early and GPR of seismic exploration,by given an initial simple model,according to the waveform of the traveltime and amplitude,phase,and decreases with least-square method observation data and theoretical simulation data,and precise location and size of the geologic body,get the optimal model to improve the resolution.In this thesis,a single medium parameter model of dielectric constant and conductivity and a complex model of multi-strata and multi-anomaly bodies are set up in the forward modeling of two-dimensional detection of GPR electromagnetic waves.The effects of the conductivity and dielectric constant in the model on the direct,transmission and reflection of the wave are analyzed.The forward real-time wave field map,waveform array map and the amplitude data received at each receiving point are obtained.The influence of the change of electrical conductivity on the attenuation of electromagnetic energy is obtained.The frequency when the relative dielectric constant changes will affect the conduction velocity of the electromagnetic wave.The propagation and attenuation of wave in single medium and complex medium are studied.The forward data and calculation directly affect the calculation of full waveform inversion.Therefore,the accuracy and iteration efficiency of full waveform inversion imaging are directly affected by the quality of forward simulation and the choice of the method.Full waveform inversion imaging requires a lot of calculation and iteration to continuously reduce the fitting error and finally get the inversion results that are closest to the real model.By adjusting the medium parameters of the model,the resolution of the inversion imaging of a single conductivity and a single dielectric constant,as well as the identification of strata and abnormal bodies are studied.The results show that the dielectric constant imaging is more reliable in the identification of abnormal bodies,while the conductivity imaging is more reliable in the identification of strata.By adjusting the arrangement of radar transmitting points and receiving points,the influence of the arrangement on the imaging results of electrical conductivity and dielectric constant inversion is analyzed,and the possible factors causing the different results are analyzed.Finally studied the dielectric constant and conductivity double parameters inversion,although double parameters inversion involves more parameters,the result will be affected by the coupling parameter,the effect not beautiful,but double parameters inversion has more than one parameter inversion underground target characteristics of the electrical parameter information,so in the process of inversion of double parameters inversion imaging also plays a very important research significance.