Common Offset Ground Penetrating Radar Data Inversion Based On Ray Theory

With the rapid development of China ' s economy,urban traffic is becoming more and more busy,so the construction and maintenance of urban roads is particularly important for traffic safety.Ground penetrating radar is widely used in highway structure and quality detection because of its non-destructive advantages.By using the amplitude,waveform,two-way travel time and other parameters on the radar profile,and through different data processing and analysis methods,important information such as the structure below the survey line,the position and geometric shape of the target body,the geological stratification and the electromagnetic properties of each layer of medium can be inferred.The main content of this paper is to realize the inversion of common offset ground penetrating radar data based on ray theory,to prove the feasibility and effective scope of application of this method and to explore the factors affecting the accuracy of inversion results.At present,there are many kinds of inversion methods for ground penetrating radar,but the error between inversion results and real data is usually reduced by increasing the time complexity of inversion algorithm,and the number of iterations is increased in the inversion process,resulting in a substantial increase in computing time.Therefore,it is of great significance to study accurate and efficient inversion methods.In this paper,the inversion method of common offset ground penetrating radar(GPR)data based on ray theory is used to estimate the thickness and velocity of each layer,and then the relative dielectric constant of each layer is obtained to realize the inversion of underground layered structure.In the inversion method based on ray theory,the offset distance between antennas,the propagation speed of electromagnetic wave in the first layer medium,the picking amplitude of each reflection interface and the reference amplitude are needed as input data.The forward modeling of the established layered terrain model is carried out by the finite-difference time-domain(FDTD)method to obtain the synthetic data.The inversion method is applied to the synthetic data to obtain good results,which verifies the feasibility of the inversion method.The main factors affecting the inversion method are discussed,including the zero-time correction method,the influence of thin layer thickness and the influence of layers.It is found that the zero-time correction method has a great influence on the layer thickness information in the inversion results.The inversion results of the thin layer with thickness less than have small errors,and the layer velocity and layer thickness of the inversion results in deeper strata are larger than the actual value.By processing the measured data of a railway section,a set of data preprocessing process is summarized,including DC elimination,zero time correction,inverse gain,spherical diffusion amplitude compensation,band-pass filtering,amplitude and travel time information extraction of reflection interface.The inversion method is applied to the measured common offset ground penetrating radar data to prove the feasibility and effectiveness of the inversion method based on the ray theory.In order to promote this method,a common offset ground penetrating radar data inversion software based on ray theory is developed based on Matlab GUI platform.The software can import the synthetic data of the mat format and the measured data of the dzt format.The software function includes all steps of the preprocessing of the measured data.It supports human-computer interaction to extract the amplitude and travel time information of the reflection interface,and realizes fast,efficient and accurate processing of data and imaging of the inversion results.