Capacitive-coupled electric-field sensing for urban sub-surface mapping: motivations and practical challenges

Ground penetrating radar (GPR) technology is increasingly deployed as the survey tool of choice for urban sub-surface mapping due to its relatively fast speed and minimal ground intrusion. However, there are several application scenarios that still pose difficulties for a GPR, for example in mapping an area with heavy clay or when presented with shallow plastic pipes. A capacitive-coupled electric-field sensing technique is herein considered for the non-intrusive detection of shallow non metallic targets. This technique relies upon detecting an electric field associated with the variation of current density as a result of changes in ground impedance. This paper briefly reviews the theoretical underpinning of the sensor system, followed by a proposal of system design with the aim of operating as an aid to existing GPR technology in urban subsurface mapping. The quality of received signal is measured in comparison with those obtained using ground electrodes. A discussion on the practical challenges associated with the application of this technique is presented, along with preliminary trial results.