Research On The Migration Imaging Method Of Ground Penetrating Radar With Antenna Pattern Correction

Ground penetrating radar(GPR),as an effective non-destructive method for detecting shallow underground targets,is widely used in engineering quality detection,hydrogeological prospecting,planetary exploration and other fields.Migration can return the slanted medium reflecting surface to the real underground interface and make the diffraction wave converge,so that the underground medium structure distribution can be obtained accurately.Due to these advantages,migration is always a research hotspot in GPR signal processing.However,when using the migration imaging algorithm,the point source,as an ideal antenna model,is used to implement the wave-field extrapolation and to describe target scattering,which makes the electromagnetic wave vector propagation characteristics of the actual transceiver antenna be ignored.This paper focuses on improving the imaging performance of GPR by apply the antenna radiation pattern correcting to migration.In this paper,the radiation pattern of ground penetrating radar(GPR)antenna is studied.Through numerical simulation analysis,it is found that with the increase of frequency,the antenna's main lobe becomes narrower and its directivity becomes stronger.In addition to being determined by the antenna design itself,its directional pattern is also deeply affected by the electrical parameter characteristics of underground soil and humidity,etc.In this paper,the radiation pattern of the infinite line source on the far-field and half-space condition is derived,and the results show that the shape and critical Angle of the pattern vary with the relative dielectric constant of the underlying medium.In order to further study the radiation characteristics of GPR antenna and the influence of soil,this chapter designs a GPR antenna pattern measurement experiment.Considering that frequency domain inverse time migration can reduce the time complexity and the shape of the antenna pattern vary with frequency,this paper proposes a pattern correction method for frequency domain reverse time migration.To verify the feasibility of this method,numerical forward modeling with antenna and multi-frequency point antenna pattern data were obtained by using CST Microwave Studio.The results show that the target scattering signal in the corrected reverse time migration image is enhanced and a more focused image is reconstructed.In addition to being determined by the antenna design itself,the antenna radiation pattern is also affected by the electrical parameter characteristics of the underground soil and its humidity.Therefore,compared with the full-space pattern,the antenna pattern in the half-space below the ground need to be paid more attention to.In this paper,diffraction stack migration is corrected by introducing the far-field half-space pattern of infinite line source.The feasibility of this method is verified through both the numerical simulation and laboratory experiment.The results show that the image with pattern correction is migrated better,the undesired extended diffraction wave in the target edge is inhibited,the anti-noise performance of the image is improved.In addition,the above conclusions are further verified by comparing with the Kirchhoff migration image and the corrected 3D diffraction stack migration.