Ground Penetrating Radar Technology
Ground penetrating radar is a wave-based electromagnetic geophysical method that fundamentally detects interfaces between materials possessing varying electrical (dielectric) characteristics. A typical digital GPR system consists of transmitting and receiving antenna elements, which emit outgoing electromagnetic pulses into the media being investigated and receive incoming reflections from this media; a central control unit which governs the characteristics of the transmitted electromagnetic waves, processes the received signal by amplifying and recording it and converting it to a digital format; and a color computer video display unit that receives the digital information from the control unit and, after processing the information through the GPR acquisition software, produces a graphical representation of the acquired data as a real-time two-dimensional continuous depth profile, which includes horizontal antenna position and vertical target depth and amplitude information. GPR operates by emitting electromagnetic radar impulses into a media (pipe) at a high repetition rate, from an antenna array towed through the pipeline. Reflections occur at interfaces of materials with differing electrical characteristics (dielectric permittivity). Reflections of various amplitudes (Figure 8) are produced at these interfaces and are detected by the receiving antenna element, depending on the incoming signal frequency, the magnitude of the difference in dielectric constants of the two materials. Additional information on GPR may be found in Holmes (2004).
Current state-of-the-art GPR systems have evolved into compact, reliable, user-friendly instruments able to be operated from start to finish by a well trained, technically experienced individual. Today’s systems allow a single user to acquire and interpret large amounts of project data in a relatively short amount of time as well as the ability to transfer the information in real time.
Along with technological advancements in recent GPR systems comes an increase in available situations to apply the technology. Beyond the historically scientific applications in the geological, archaeological, or research realms, GPR has recently been increasingly applied for utilitarian purposes in the environmental and trenchless technology industries to locate and assess subsurface objects.