GPR is a relatively new geophysical technique. The last decade has seen major advances and there is a general feeling that the technology is reaching a level of maturity. The history of georadar is closely tied to the various applications of the technique. GPR has the broadest set of applications of any geophysical technique.
As a result, the spatial scales of applications and the diversity of instrument configurations are vast. The value and limitations of the method are better understood in the global user community. The purpose of this article is to provide a brief history of the method and an overview of current trends, while outlining potential future developments.
GPR Detection – What is GPR?
GPR (ground-penetrating radar) is used in many areas to observe artificial and natural elements. GPR allows for the detection of underground tanks, metallic and non-metallic pipes, power lines, water pipes, rebar and post-tensioning cables inside concrete.
GPR waves are equal to those of a cell phone or wifi network, while X-rays require a clearance of 50 feet before being used for safety reasons. In general, ground-penetrating radar is the most cost-effective option and the fastest method of testing concrete. The principle of using radio waves to determine internal soil structures has long been known.
Among the earliest works in this field, the use of radio echo sounders to determine the thickness of ice sheets in Antarctica and the Arctic and to measure the thickness of glaciers is undoubtedly the most successful. Underground detection by GPR in non-glacial areas was initiated in the early 1970s. The first achievements focused on work on permafrost soils.
Underground detection by GPR – Evolution of GPR
Originally developed to measure the thickness of glaciers in the 1930s, the hardware and software made huge technological advances in the 1960s and 1970s, finally becoming affordable in the mid-1980’s.
GPR has much higher resolution, making it easier to process the data and render subsurface images. It is also quick and cost-effective. Coarse-grained, low-conductivity deposits such as sand and gravel are ideal deposits to map in detail with ground-penetrating radar, as opposed to clay-rich deposits that absorb and limit signal penetration.
From 1900 to 1955, copious research was conducted on the propagation of radio waves over and along the earth’s surface. Although several hints were given about the possibility of using radio waves to probe the subsurface, there were no reports of any successful measurements of this type.
After 1950, the first reported attempt to measure subsurface features with radio wave signals was reported. El Said attempted to use the interference between signals transmitted directly through the air and signals reflected from the water table to image the depth of the water table.
From 1975 to 1980, applications began to grow due to the availability of technology and a better understanding of geology. The Geological Survey of Canada explored a number of applications, the main one being a better understanding of the permafrost terrain in the Canadian Arctic. Proposals for pipelines from the Arctic to transport oil and gas to southern markets have generated much interest in engineering in frozen ground and environments.
From 1980 to 1985, interest in GPR declined to some extent. Initial optimism about the technology gave way to the reality that many environments were not conducive to GPR. There was considerable confusion as to whether the failures were equipment-related or due to natural material responses. In addition, very little money was available for technology development.
From 1995 to 2000, the evolution of computers led to great advances in georadar. Digital modeling of complete 3D problems became possible, although still with large computers. The ability to handle large volumes of information in digital form and to manipulate it quickly became routine.
GPR Detection – The Future of GPR
Today, GPR is considered a primary tool for a wide range of businesses and academic disciplines. Archaeologists and forensic scientists use GPR to identify buried structures, human remains and artifacts without risking damage. In engineering and construction, GPR is used for everything from the initial analysis of the construction site and the location of existing utilities to the location and evaluation of structural steel and voids in concrete walls and floors.
In the military, GPR is used to identify landmines and booby-trapped devices in combat zones so that they can be safely avoided or disposed of. GPR is used in a wide range of geological disciplines for everything from conducting geological surveys to measuring the depth of polar ice, locating accessible groundwater deposits, and even fossilized dinosaurs and other paleontological remains.
Conclusion
GPR is designed for surface applications where the transmitter and receiver are above ground. Nevertheless, there are applications where the GPR must fit into a narrow borehole that can be more than a kilometer long. These measurement tasks are performed with a borehole radar as a special tool. Feel free to contact us or call us for more information about underground detection by GPR.