Most types of radar are used to detect objects such as vehicles, ships, airplanes and even storms. This means that this technology is most often used to locate and distance objects on the surface. Once a tool used only by the military and academics, technological advances have allowed these same radar techniques to measure and detect objects below ground on a commercial level.
Ground penetrating radar, otherwise known as GPR, is a geophysical method of locating and measuring objects underground. Similar to surface radar systems, it works by sending pulses of electromagnetic energy into the target area and measuring changes in the reflections of the energy pulses to determine the location and depth of the target object.
What is GPR?
Ground-penetrating radar is used in many areas to observe man-made and natural features. Ground-penetrating radar can detect underground tanks, metallic and non-metallic pipes, power lines, underground conduits such as water pipes, rebar and post-tensioning cables inside concrete.
Ground-penetrating radar 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 have undoubtedly been the most successful. Ground-penetrating radar (GPR) monitoring or detection in non-glaciated areas was initiated in the early 1970s. The first achievements focused on work on permafrost soils.
How does GPR work?
GPR is clearly a fantastic solution for locating underground utilities. However, the applications don’t stop there. In addition to utility mapping, contractors are looking for rebar under structures or concrete slabs and underground storage tanks.
Surveyors could also benefit from using the georadar to help them learn about soil conditions and potential hazards or underground targets to monitor. Ground-penetrating radar can also detect the presence and location of groundwater, as well as the amount of groundwater in a subsurface bedrock.
Properties of GPR
The depth and humidity of certain environments cause the signal to be reduced very quickly. This phenomenon is also observed in certain soils, notably clay. It is complex to analyze the representations obtained in a heterogeneous environment because it is difficult to differentiate natural obstacles from a pipe. It is often necessary to make a graphic representation in a different orientation.
As a precaution, it is preferable to calibrate the radar according to the environment because it can modify the scattering rate. Changes in the nature of the soil are also a problem in the analysis. The implementation of this method and the analysis require specialized personnel despite recent advances in image processing tools.
Thanks to GPR detection or georadar inspection, it is now possible to locate all types of metallic conduits. GPR survey or georadar detection includes even wires with a suitable diameter and shallow PE pipes with a diameter greater than 63 mm. For small diameter PE pipes, these results are problematic. These are pipes with a diameter of less than 40 mm. Thousands of connections will fail to be detected because they are not well-mapped.
With GPR survey, a “visible” pipe can be traced with impeccable accuracy. It completes the whole process of detection by georadar by its flexibility. It is possible, thanks to the results obtained, to certify the location of a structure already identified. GPR detection can locate pipes and pinpoint their precise position, up to 4m deep depending on the version. It is also possible to add a GPS for geolocation.
How accurate is GPR detection?
When it comes to locating objects in underground materials, ground-penetrating radar is incredibly accurate. A computer records the strength and return time of the electromagnetic pulses and uses sophisticated filters, called algorithms, to display this information on the operator’s screen. When the operator knows how to interpret these readings, the ground-penetrating radar is a powerful device.
The accuracy of the ground-penetrating radar depends on several factors, including the frequency of the radar and the accuracy of determining the dielectric constant of the surrounding material. Understanding how these elements work together can improve the accuracy of these systems. Targets such as pipes, telecommunication cables, rocks, and even buried artifacts can generate this same type of arc on the screen.
However, due to a host of variables, hyperbolas sometimes do not show up clearly in the data. Instead, we see a disturbance. Perturbations appear as a mess of data. This is often evidence of an installation trench, as there is no way the ground will be the same after excavation as before.
Conclusion
GPR detection is a very effective method for locating buried objects. This tool has many advantages such as ease of use, speed of detection, prevention of problems, etc. For more information on GPR in Montreal, do not hesitate to contact us now!