Research On GPR Tomography And Electromagnetic Resonance Recognition Technology Based On Urban Geological Hazard Exploration

Along with social progress and science development,city geological environment is increasingly affected and pressured by the more frequent human activities and a large number of human projects.It keeps changing the geological environment and accelerates its deterioration.Consequently,city geological hazards have shown a growing trend.To ensure the healthy,safe and well-ordered city operation,it is necessary and urgent to identify these geological hazards,which must be relies on combination of geological survey and geophysical exploration.This dissertation studies the application of ground penetrating radar(GPR)in city geological hazards exploration.The.imaging method of ground penetrating radar based on electromagnetic theory is similar to traditional seismic exploration technology.Herein,the finite difference time domain(FDTD)method of electromagnetic field is used to study the detection model of ground penetrating radar(GPR).3-D forward imaging of common geological hazard models is carried out.A practical 3-D imaging software is designed to perform 3-D imaging of 2-D GPR data.3-D imaging is an inevitable trend in the development of ground penetrating radar(GPR).Most of its maps can be directly recognized by geological interpreters.But for a large number of image discrimination and multi-target,complex target state;how to automatically identify the target,improve the recognition accuracy and reduce the labor intensity,is still the current application of GPR difficulties.Herein,the longitudinal time domain data of the object in 3-D images are used to identify the poles using the electromagnetic resonance characteristics of the object half space.The application of electromagnetic resonance theory in ground penetrating radar(GPR)is still in its infancy.The singularity expansion method based on resonance region is an important milestone in the development of transient electromagnetic field theory.This method can be employed to describe the characteristics of the target with fewer feature poles,which greatly reduces the complexity of the recognition system.This method has achieved great success in the military field,however,its application in the main detection field of half space is still not very advanced.The electromagnetic resonance in medium space and half-space is studied for the electromagnetic transient scattering model of common basic shapes.3-D FDTD method is used for forward modeling,and matrix beam method is used to extract the poles of the late resonance section of the time-domain curve of radar echo signal.The result of extraction is consistent with the theoretical solution.The electromagnetic resonance characteristics of metal sphere,dielectric sphere,spherical cavity,spherical cavity filled with water,rectangular cylinder,cylinder and cylindrical cavity filled with water in medium space and half space are studied respectively.For the scattering echo in half space,S VD deconvolution is used to remove the influence of the interface in half space.The 3-D model of irregular object is built by constructing HDF5 file,storing the 3D model data in HDF5 file,and then the irregular 3D model is constructed by gprMAX.For the complex electromagnetic scattering model with different water levels injected into the cavern,the variation law of the resonance pole with the water level rising is studied.Based on the analytical solution of electromagnetic scattering from a cylindrical object in half space of ground penetrating radar,its scattering characteristics are investigated theoretically.The analytical solution of electromagnetic scattering from an eccentric dielectric cylinder excited by on-line current source and plane wave source is obtained by mode matching method.The solution is highly consistent with the numerical results in the case of concentric and eccentric columns.The expression is simple and the calculation speed is fast.It is of great significance for fast calculation of scattering properties of cylindrical objects in half space and further study of the nature of electromagnetic resonance of objects.The above research results can be used to detect,identify and interpret potential geological hazards,such as caves,underground rivers,rock columns,faults,etc.It is of great value to improve the ability of urban disaster prevention.