Forward Modeling Research Of Ground Penetrating Radar Pipeline Detection Based On FDTD

In actual pipeline detection work,due to the actual underground each layer of the composition of the material is not the only,as a kind of substance and its surrounding dielectric sex differences,will show in the radar profile with the different anomalous reflection,the physical shape is different,also show different response characteristics,which increased the difficulty of the GPR data interpretation.Therefore,it is very necessary to carry out forward simulation research.It is of practical significance to fully study the characteristic curves of different pipelines and interpret the data of actual detection work.Forward through software simulation,the simulation results of direct wave of energy is greater than the reflection signals,underground pipeline buried depth is shallow near the surface,the effective of GPR signal will be covered by the strong direct wave,in addition,local pipeline under the reflection signal is weak,but because of the strong direct wave,can make the pipeline reflection of hyperbola is not obvious and even hard to find.Therefore,the elimination of GPR signal direct waves is very important to improve the quality and interpretation accuracy of forward simulation images.In this paper,gprMax3.0 software based on FDTD(finite difference time domain)is used to carry out several groups of GPR forward modeling experiments,to explore the influence of different parameters on forward modeling.The singular value decomposition(SVD)method is used to process the forward modeling data,which improves the quality of the forward modeling data.Finally,the pipeline detection results are analyzed with an engineering example.Through the above work,the following conclusions are obtained:The underground pipeline reflects the hyperbola,with the highest energy at the top and gradually weakening towards both ends.The conductivity of the formation media has an obvious influence on the propagation of electromagnetic waves.The higher the conductivity is,the more serious the attenuation of electromagnetic waves is.Generally speaking,the larger the pipe diameter is,the stronger the reflected signal will be.The deeper the pipeline is buried,the stronger the reflected signal will be.According to the hyperbolic top reflection time,the buried depth of pipeline can be calculated.Using the top and bottom reflection time of hyperbola,the pipe diameter can be calculated.GPR can detect metal pipeline better than non-metal pipeline.Two horizontal parallel pipelines are distinguished only when the spacing between them is greater than 1/4 of the diameter of the Fresnel strip.Two vertical parallel pipelines can be distinguished when the spacing is greater than ?/ 4;With the increase of the number of layers,the electromagnetic wave loss increases and the reflected signal becomes weaker.Singular value decomposition(SVD)has a good effect on removing direct waves from forward simulation data.According to the experimental summary,it is better to remove the first singular value and restore the GPR profile with all the remaining values.