Ground Penetrating Radar Services
Ground penetrating radar (GPR) is basically a radar, as its name indicates. But unlike most radars sending and receiving electromagnetic (EM) waves through air, GPR directs its EM waves down into the ground and receive wave bounce backs from objects buried underground, thus revealing their presences and locations. So GPR is basically a non-destructive subsurface scanning tool, used in many ways like a metal detector. But compared to metal detectors, GPR operates in a much higher frequency range, giving it three main advantages over metal detectors. First, it detects not only metallic objects, but also non metallic objects such as PVC pipes septic tanks and even voids. Second, GPR can provide great details of buried objects, such as their shapes and depths, preventing a lot of false positives in common metal detecting. A good example is underground storage tank (UST) locating. A metal detector can respond to steel USTs, but also other underground objects containing metals such as reinforced concrete and junks. It's hard to tell their differences through metal detecting alone. Since the shape of an UST such as a heating oil tank is usually cylindrical, if the GPR scanning can reveal the shape of the buried object, you can better tell whether it's an UST or not, thus reducing false positives. Third, since the majority of wave energy emitted by GPR is directed downward (like a laser but in a less extend), the interferences from surrounding and aboveground objects are minimal, making GPR more suitable than metal detectors in indoor scanning.
Although GPR is a great subsurface scanning tool, it does have its limitations. Varieties of GPR types are available according to penetration depth and resolution requirements. Also, GPR is commonly used with other scanning tools to compensate its limitations. Choosing types of GPRs and other scanning tools should be based on the properties of target objects and the environment they are in. Our experts in GPR and geophysics will be glad to help you to evaluate the options.
Our GPR services include but not limited to:
- Underground utility locating
- Concrete scanning
- Underground storage tank (UST) locating
- Underground void locating
- Septic system delineation (septic tanks, septic fields, cesspools and related piping)
- Historical burials mapping and archaeological mapping
FAQ
GPR stands for ground penetrating radar. It's a non-intrusive subsurface scanning tool. GPR works in a way like ultrasound, only that GPR uses electromagnetic (EM) waves instead of sound waves. It works by sending out electromagnetic (EM) waves into the ground and observing the EM waves bounced back by buried objects.
GPR penetration depths vary from a few inches to tens of feet or even more. It depends on the frequencies it uses and properties of subsurface materials. GPR works the best over materials with low electrical conductivities such as dry sandy soils and the worst over materials with high electrical conductivities such as wet clayey soils. More often than not GPR waves can penetrate through asphalt or concrete pavements, but not metallic objects such as steel plates or aluminum walls.
We have used GPR to find many subsurface objects such as pipes, cables, conduits, oil/gas tanks, voids, concrete reinforcement, cemetery burials, septic tanks/fields, tunnels, etc. But keep in mind that for a successful GPR scanning, at least two conditions should be met. One is that the GPR penetrating depth needs to be good enough for reaching the target depth. The other one is that there should be enough property contrasts between the target and the surrounding soils. Unfortunately, more often than not, we don’t know whether these two conditions are met until we try it at the very survey area/location.
From GPR scanning, you can usually get horizontal locations of the targets accurately, but not their depths. It's like observing stones at the bottom of a river from a boat. You can see where the stones are exactly, but you can only estimate their depths. The deeper the river bottom is, the harder to get their exact depths. While a sonar can get a pretty accurate depth of a river, GPR usually needs to see through varieties of subsurface materials much more complicated than the water in a river, the view of GPR can be greatly distorted, making the depth estimation much less accurate. There are some techniques helping to make more accurate depth estimations, and more or less they are based on some assumptions about subsurface materials. These assumptions may or may not be true. Cautions must be taken if the depth estimation is critical for your projects.
GPR scanning is not hazardous. Unlike X-Ray, the typical EM radiation from GPR is less than what a cell phone emits. No special cautions or business interruptions are required.