Realistic Expectations for Deep Ground Penetrating Radar Performance

Abstract

Ground penetrating radar (GPR) is unique amongst geophysical tools in terms of its imaging resolution and the diversity of its applications. Since its commercialisation four decades ago, GPR has also been distinguished because of the prevalence of some of its purveyors to oversell the method’s capabilities, relying largely on the end users’ lack of understanding of the underlying physics. Early adopters in the 1980s and 90s were dismayed to find that environments suitable for its purported ubiquitous deep penetration capabilities were rare and that it required resistivities well into the 1000s of Ohm m. Regardless of the advances made in electronics and antenna design in the intervening decades, the fundamental limitations have not changed. Misconceptions, “specsmanship” and hype have continued to abound in the GPR marketplace, particularly in recent years. Systems purporting to penetrate hundreds of metres using “megawatt” transmitters from the former Eastern Bloc have been promoted for mineral exploration, particularly in Australia and Africa. Other pseudo-radar concepts, such as the use of beam forming to achieve kilometres of penetration with centimetre accuracy, or THz laser scanners which can detect individual diamonds deep underground, have generally targeted junior exploration groups who lack in-house geophysical guidance. This work provides an overview of the fundamentals of non-dispersive EM wave propagation in the ground and an examination of the recent published performance claims of some GPR and pseudo-GPR systems within the context of accepted EM theory. The accepted methods for potentially increasing GPR performance, given the emerging technologies such as novel transmitter and receiver designs and new GPR antennas, are also discussed.