Ground Penetrating Radar or GPR is a non-destructive means of generating a profile of subsurface structures and features. GPR scanning services produce an image of underground features which can be used to identify the location and depth of buried structures. The images produced also can aid in determining soil type, structure and condition. In short, GPR scanning services provides a cost-effective method to determine the possibility of buried objects without disturbing the surrounding soil.
GPR units consist of an antenna in a cart, which is dragged or rolled over the soil. Within the cart, a video screen/data logger records the signals received via radio waves. Here’s how that works: the GPR antenna transmits pulses of high frequency radio waves into the soil. The transmitted radio waves then reflect back to the antenna. Variations in soil conditions and buried objects alter the reflected radio waves. These waves produce the digital images that are recorded by the GPR. These are not photo-quality images of a buried object, but instead illustrate a reflection of the object. Our trained technicians will then interpret the reflections to indicate the presence of a specific object.
How GPR Works
Ground Penetrating Radar Variables
Although Ground Penetrating Radar Services are very useful for scanning large areas and for determining the location and depth of previously unknown objects or soil conditions, the procedure does have limitations.
This is a measure of how well an electromagnetic signal may pass through a material. The lower the soil conductivity, the farther a signal may travel. In terms of GPR scanning units, the lower the soil conductivity the deeper scanners can “see” into the soil.
- Dry, sandy or granite soils have a low conductivity.
- Clays, shale or soils saturated with water have a high conductivity and consequently may limit or even eliminate the ability of GPR services to penetrate the soil and provide workable signals.
The frequency of Ground Penetrating Radar Services’ antennas affect how deep they can see and how much detail they can resolve.
- Low frequency antennas (25-200 MHz) can penetrate deep into soils but provide low image resolutions. These are typically used to identify soil geologies and structures such as soil stratification, sinkholes and fractures.
- High frequency antennas (300-1000+ MHz) can only penetrate a short distance into soils (from 10-15 feet down to a few inches) but can produce very detailed images of the soil and buried objects.
Pipe and/or Cable Diameter
The signal that is broadcast from a GPR services antenna extends downward and outward, much like the ripples in a pond. The lower the soil conductivity, the farther a signal may travel. In terms of GPR units, the lower the soil conductivity, the deeper they can “see” into the soil.
Roughly translated, for each foot in depth that an object is below the surface, it must increase by an inch in diameter. For example, a pipe that is buried 4 feet deep must be at least 4 inches in diameter. Small diameter pipes or cables or those that are buried very deeply, may not be locatable using a GPR scanning unit.
For more information about ground penetrating radar services, please click here to fill out our form, click here to email us, or call PULS, Inc. at 1-800-883-6855.