How Ground Penetrating Radar (GPR) works

Ground Penetrating Radar is a cutting edge non-destructive technology that is extensively used in various fields like construction, locating utilities and pipes underground, bridge and road inspection, concrete inspection, geology, archaeology, etc. It can be used over a variety of media such as rock, ice, soil, water, concrete, pavement, and structures as well as to locate all types of underground substances. It is more recently coming into popularity for concrete and bridge inspections as well as for construction to locate underground pipes and electric before digging

How it works

GPR or Ground Penetrating Radar uses high-frequency Radar pulses or electromagnetic waves which usually fall into the range of 10 MHz to 2.6 GHz to scan the subsurface. Radar (Radio detection and ranging) is a technology used to detect the target in free space and determine its range.

A GPR setup consists of a transmitting and receiving unit, control unit, display console, and power supplies. It sends an electromagnetic pulse through an antenna which penetrates the surveyed surface and portion of energy deflect back to the receiving end when the wave encounters any obstacle under the surface.

The returned signal is then stored digitally so that the computer can calculate the travelling time of the signal to and from the target. This assessment helps in indicating the depth and location of the target. The result is displayed on the console unit.

Data collection on different surfaces

GPR is used on the ground to find the depth and location of buried objects. The radar unit can send and receive signals up to 1000 times per second. The field operator checks the reflected signals and stores it in the system so that it can be used for further analysis.

It is used on concrete surface to locate targets like rebar, conduits, and post tension cables. A high-frequency signal is used to scan the concrete structure. The data is depicted in form of a grid format to generate a map of objects located in concrete while the line scan is used for determining the thickness of it. It is used in creating the 3D maps of the target and determining the depth as well.

Data interpretation

Since the GPR signals traverse through different types of material like concrete, soil, debris, etc. therefore the resultant data is quite complex. Although, the result is illustrated in graphical form but It still requires high expertise to interpret the findings.

The accuracy of the GPR services is based on elements beneath the surface and frequency of waves used to emit and receive signals from the antenna. For example, while evaluating targets in a concrete structure like rebar or conduit, higher frequencies like 1000 MHz is required for producing high-resolution illustrations. It can provide details of the depth up to 24 inches.

On the other hand, If deep penetration is required on subsurface like soil then low-frequency wave ranges from 12.5 MHz to 500 MHz is used.