Research On Velocity Estimation And Imaging Algorithm Of Ground Penetrating Radar Signal In Layered Media

Ground penetrating radar(GPR),is a modern nondestructive ground detection technology that uses electromagnetic wave propagation between different media to perform parameter inversion,imaging,detection,and identification of the underground environment.Unlike airborne radar,in the detection environment of GPR,the objects are often various soils,road materials,water,etc.The electromagnetic characteristics of different types of materials not only vary greatly,but also in the same substance,the electromagnetic characteristics changes with the influence of outside air humidity,temperature,etc.The electromagnetic properties of the substance determine the propagation speed of electromagnetic waves,etc.This parameter determines whether the subsequent imaging is accurate and has important significance.In common wave velocity estimation algorithms,there are few algorithms designed for GPR detected by profile method.On the other hand,in many working environments,such as highways,bridges,and even lunar soil are layered media structures,this puts higher requirements on wave velocity estimation and imaging algorithms.This paper studies the wave velocity estimation and imaging algorithm of GPR detected by the profile method for the layered medium environment.Because the original GPR echo contains strong surface reflections and noise from the system and the environment,this article first preprocesses its echo data.After providing echo data for post-processing,the algorithm of image entropy and frequencywave number domain(F-K)migration is used to estimate the wave velocity from a single layer of medium,and then the F-K algorithm is improved,and it is proposed that the lower layer can be used.Because the Back Projection(BP)algorithm model is simple and highly portable,this paper introduces it into the imaging of layered media,proposes a BP algorithm that is carried out in sections,and solves the problem of large calculation amount of the traditional BP algorithm.The improvement of the BP algorithm,and on the basis of the fast BP algorithm,in order to solve the problem of side lobes and clutter interference,an auto-correlation BP algorithm is proposed,and the effectiveness of the algorithm is verified.In view of the complex calculation of BP algorithm for imaging of multi-layer media and the difficulty of estimating the refraction point,the paper then conducted a study of the Finite Difference Reverse Time Migration(FD-RTM)algorithm,which can be used in the imaging of multi-layered media.Make up for the shortcomings of BP algorithm.First,the traditional FD-RTM algorithm is introduced,but the wave equation is approximated in the calculation process,which causes the problem of poor focusing ability.For this,the author also performed a Linear Transformation Finite Difference Reverse Time Migration(LTFD-RTM)algorithm,and for layered media to improve on this basis,proposed a segmented LTFD-RTM algorithm,and experiments to verify the effectiveness of the algorithm.Finally,the measured data is processed,and the applicable conditions,advantages and disadvantages of the algorithm are further analyzed,and the future research direction is prospected.