Ground Penetrating Radar (GPR) for Underground Utility Locating and Concrete Imaging

Ground Penetrating Radar (GPR) offers a powerful, non-destructive method for detecting and imaging subsurface structures. This technology uses radar pulses in the UHF and VHF bands of the radio spectrum, which emit electromagnetic energy to locate buried objects and features beneath the surface.

A GPR system transmits high-frequency radio waves through a surface using a specialized antenna. When these waves encounter buried objects or changes in material properties (such as boundaries with different dielectric constants), the receiving antenna detects variations in the reflected
signals. This approach is similar to reflection seismology, capturing both velocity and amplitude changes in the return signal to create a detailed underground map.

GPR effectively evaluates the internal structure of floors, walls, and concrete elements, including steel reinforcements. However, the depth it reaches depends on the medium’s electrical conductivity and the radar’s transmitting frequency.

While higher frequencies provide sharper resolution, they do not penetrate as deeply as lower frequencies, and materials such as dry sand or massive dry rock (like granite) allow GPR signals to reach up to 50 feet below the surface.

Ground Penetrating Radar calculates the depth of underground objects by measuring the travel time of radar waves. Using an estimate of wave propagation velocity, field technicians can accurately calculate the depths of buried features or interfaces.

Limitations of GPR Technology

As with any technology, GPR has its limitations. Radar waves, for instance, cannot penetrate metal, making it impossible to scan the interior of steel tanks or assess their condition. Additionally, objects located behind metal surfaces may be obscured, limiting visibility. The performance of GPR depends on the sensor’s capabilities, the properties of the target, and the surrounding environment. While a target may be detectable at shallow depths, the same object might become invisible as depth increases.