In-pipe GPR configuration and the determination of target depth and ground permittivity

Ground Penetrating Radar (GPR) is frequently used to survey roads, pavements and other sites. To determine the depth of the targets found the permittivity of the ground needs to be established or eliminated from the analysis of the GPR data. A novel way of using bistatic GPR equipment is to place the transmitters and receivers at the surface of the ground and in an available pipe. Measurements through the ground of signal delay can then be analysed to reveal the permittivity of the ground, and therefore establish the depths of targets in the vicinity of the pipe. This paper examines measurement and analysis techniques for such a scheme, and reports on a measurement system that has been developed. The influence of multiple reflections caused by the in-pipe location of antennas is examined and a relatively simple impulse response model is proposed that appears to be sufficient for deconvolving the multiple reflections out of the measured data.