Ground-penetrating radar (GPR) uses electromagnetic waves that are transmitted from an antenna into the ground. Reflections off subsurface objects or stratigraphy are detected by the receiver antenna and analyzed to obtain information about the structure and characteristics of the ground beneath. The radar signals are processed to provide a real-time radar image of the ground which can be displayed as profiles, planview maps isolating specific depths or three-dimensional models.

GPR is a non-invasive and safe method of surveying and is ideal for utility location surveys as it does not require excavation. It is also useful for locating non-metallic objects such as conduit, rebar and post-tension cables that may be hidden within concrete. It can also reveal voids, fractures and structural layers.

Understanding Ground-Penetrating Radar Technology

Performance is affected by the electrical conductivity and mineral content of the scanned medium. High conductivity and salt contaminated material will attenuate the electromagnetic signal leading to reduced penetration depth. GPR is also unable to penetrate through metallic structures, including dense reinforcement.

The most common type of GPR equipment consists of an antenna mounted on a push cart which is driven over the site to be surveyed. The transmitting and receiving antennas are tuned to a specific frequency range which is determined by the desired penetration depth and resolution. The data is collected on a real-time basis and displayed on a digital recorder. The results can be interpreted in-house during the survey process or stored for later analysis.