GPR System Locates Metallic, Nonmetallic Targets

GPR System Locates Metallic, Nonmetallic Targets
The UtilityScan ground-penetrating radar (GPR) system from Geophysical Survey Systems Inc. (GSSI)

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The UtilityScan ground-penetrating radar (GPR) system from Geophysical Survey Systems Inc. (GSSI) locates metallic and nonmetallic targets, including plastics, cementitious materials and fiberglass. It can also detect trench lines if a pipe is obscured.

“Ground-penetrating radar can detect pipes without tracer wire or those that cannot be traced with electromagnetic locators,” says Peter Masters, applications specialist for GSSI. “Having the ability to quickly and effectively locate pipe enables users to finish jobs faster and complete more jobs during the day.”

GSSI recommends using GPR in conjunction with other locating technologies, such as electromagnetic locators, metal detectors, sondes and even leak locating equipment to confirm pipe locations: The more information that can be collected, the better the decision.

Like any technology, GPR has certain limitations, Masters says. In particular, GPR antenna penetration is affected by soil type.

“Sandy soils are generally better; clay soils are generally more difficult,” he says. “The best way to find out if GPR is effective in your area is to check the USDA soils map.”

Pipe depth and pipe diameter is also a consideration.

“The deeper the pipe, the larger it needs to be for the GPR to be effective,” Masters says. “As a general rule, GPR can find all types of pipe material. However, we do use a pipe diameter-to-depth ratio as a guideline for what users can expect to see. The ratio is roughly 1 inch in diameter for every foot deep a pipe is buried – 2-inch pipe at 2 feet, 4-inch pipe at 4 feet.”

The scan offers real-time data collection with backup cursor and cross-hair cursor to accurately find targets. It can also store and replay data.

“Typically, three components make up a GPR system: the control unit, the GPR antenna and the survey wheel to measure distance,” Masters says. “GPR is looking for any point where the electromagnetic properties of the materials change. As the operator walks over the area, the GPR system sends low-power radar waves into the subsurface. The control unit then records the strength and time required for the return of the reflected signals. Subsurface variations like pipes, wire, tanks and voids will cause significant reflections, which appear on the screen in real time, enabling the operator to identify both horizontal and depth positioning of buried utilities.”

The system is available in three models. The entry level UtilityScan LT is designed for easy use, while the multifunction UtilityScan offers 2-D and 3-D data collection and display. It can operate with a range of antennas for scanning soil or concrete structures. The UtilityScan DF has a dual-frequency antenna for near-surface resolution, traditional depth ranges, an intuitive interface and display options. 603/893-1109;


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