Research On GPR Concrete Nondestructive Testing Technology Based On Full Waveform Inversion

In the construction of the project,as a widely used and important material,the quality of concrete is related to the safety and quality of the entire project.The high-efficiency and high-precision quality inspection and evaluation of concrete components not only ensures the safety of the project,but also ensures the safety of people's lives and property.Ground Penetrating Radar(GPR)is characterized by high efficiency,losslessness,and high resolution.The radar reflection profile obtained by the conventional common offset sweep method can only provide the information of the ground emission interface,and usually cannot obtain the internal electrical parameters of the target.Ground-penetrating radar tomography technology,usually using transmitted radar wave information,can easily obtain the above electrical parameters and complete the quality inspection and evaluation of concrete components.In addition,when the offset method is used to suppress the diffraction or homing reflection interface in the radar profile,the velocity distribution(relative permittivity)of the electromagnetic wave inside the object can be obtained by the chromatographic technique.Transmissive radar tomography is a technique that inverts information inside a target between a transmitting antenna and a receiving antenna.Conventional tomographic methods are based on ray theory.The method based on ray theory has a simple principle and high computational efficiency,but its theory is high-frequency approximation and can only resolve abnormal bodies larger than the main wavelength of the signal,but it can not always meet the requirements for concrete detection in engineering exploration.Transmissive radar full-waveform tomography under ideal conditions can reach one-third to one-third of the dominant wavelength,which solves the problem of inadequate resolution of the ray method in concrete detection.However,the full waveform inversion method has many problems such as large amount of calculation,slow convergence,strong nonlinearity,and dependence on the initial model.The initial model is provided by using uniform models,based on ray theory,and frequency domain methods.Different initial models have different effects on different problems.There is no unified standard so far.This article provides a more accurate initial model for the full waveform inversion method based on the ray theory,and accelerates and guarantees that the full waveform inversion converges correctly.The purpose of this project is to use the full-waveform inversion method for the detection of concrete internal structures,so as to solve the problems of the conventional scanning method such as difficult interpretation,low resolution based on the ray theory method,and the like.This paper first introduces the theory of full waveform inversion for transmission radar,and then introduces the theory of curvature ray inversion based on ray theory.This paper improves the shortest path ray tracing technology and obtains more accurate ray paths and travel times,improving the accuracy of inversion results.Second,a full waveform inversion method based on ray theory was implemented.Finally,the whole algorithm of this paper is used in the measurement of concrete cylindrical section transmission radar data,and its internal accurate velocity and conductivity distribution images are obtained,thus verifying the correctness and practicability of the proposed algorithm.