Underground pipeline map patterns received by RIS-K2 GPR

摘要

Underneath today's city streets exists a labyrinth of underground water,sewer,gas,electric and telecommunication lines.Nonmetal (PVC,PE,etc) pipe is getting more and more used in municipal construction,and it brings problem for pipeline detecting.As non-metallic utilities making the electromagnetic interference technology useless,the metal detector such as RD400 metal device can not locate these utilities.Ground penetrating radar (GPR) can be used to locate nonmetal objects.GPR is a nondestructive geophysical method that produces a continuous cross-sectional profile or record of subsurface features.Received GPR signatures are basically dependent on the electromagnetic properties of the mediums through which the energy passed through.These signatures are important for the identification and quantification of subsurface features.GPR signatures include reflection strength,signal polarity,two-way travel time,signal attenuation and hyperbolic reflection.The reflection strength and polarity is a function of the dielectric properties of adjacent media.The greater the dielectric contrast between two media,the greater the reflected strength will be.If the reflection coefficient is a positive value,the positive amplitude precedes a negative amplitude on the reflection signal.The signature of a reversed polarity is just the opposite negative amplitude followed by a positive amplitude.Two-way travel time through a given medium is typically collected at a known depth location (usually by means of manhole or inspection shaft).Hyperbolic shapes from reflections occurred when the antenna crosses a linear target (pipes,etc) situated perpendicular to the antenna path.In this study,an RIS-K2 system constructed by IDS (Ingegneria dei Sistemi SpA,Italy) was used with 200MHz and 600MHz monostatic antenna.More than 1500 GPR profiles were collected from more than 100 pipeline survey projects for different combinations of pipe types,radiation pattern.For this paper,only 6 typical GPR image examples from nonmetal and metal pipe,box shaped utilities is presented.These GPR profiles shows that,hyperbola feature is the reflective properties of all pipes,there is no multi-reflection wave for Metal(castiron and steel pipe) and concrete pipe,and there is multiple reflection wave for PVC and PE pipe filled with water,reflection is weak for PE gas pipe.In some box shaped utilities diffraction patterns can be observed from the corners of the upper part of the box.It is also explained to the typical GPR image features about adjacent and paralleled pipeline,and analysis on the reason why it is more detecting effective for PVC water supply than PE gas pipeline by diameter and permittivity.