What is GPR and How Does it Work?

Ground Penetrating Radar, often abbreviated as GPR, is a technology used to locate subsurface obstacles at construction sites, including post tension cables, rebar, pipes, cables, masonry, and more. But how does it work?

The GPR System

A GPR unit is made up of three parts: a power supply, an antenna, and a control unit with user-facing software (typically a tablet). This unit emits radar pulses, that is, high frequency pulses of energy, from the antenna. Those electromagnetic waves are then reflected, refracted, and diffracted beneath the surface. By tracking the amount of time it takes for those waves to travel beneath the surface, the unit is able to detect obstacles. The information from the antenna is then translated into a radargram. Thanks to advances in GPR technology, there is no need to download the images to another machine. Instead, the control unit translates the data into a continuous image that can be translated in real time. The resolution of the image is also much higher than some other methods, such as thermography.

It is also worth noting that while the most common image of GPR is a user pushing a wheeled unit along the ground (known as “ground-coupled”), this is not the only form of GPR. While it is the most common application of GPR, it can also be used on vertical objects, such as walls, pillars, and columns. There are also air-launched units, which are sometimes used in civil engineering contexts in quickly scan a road or bridge surface.

How Powerful Is It?

The depth at which GPR can map the subsurface depends on several factors, especially the density of the material it is being used on. Even when GPR is used on soil, the radar depth depends on the composition of that soil. Your readout will not show as much if you are using GPR on a dense material, like wet clay, versus less dense soil types.

For example, when being used on a concrete slab, units that are specific to concrete scanning can penetrate up to 16 inches. Utility locating systems can generally give reliable results up to 10 inches, but it varies drastically depending on soil conditions and composition.

Why is it used?

GPR is especially useful because it is a non-invasive method of investigating the subsurface. A common reason for using GPR in a construction site is to detect post tension cables or rebar beneath the surface. Digging without being aware of such obstacles can cause serious injury or even death as a result. It also prevents other mistakes which could complicated a construction project, such as inadvertently cutting cable wires or damaging pipelines. Aerial units are used by civil engineers to capture scans of roads and bridges, as well.  GPR is also used in non-construction contexts. For example, it is also used by archaeologists to detect buried objects of interest, and has even been used to locate unmarked graves.

Are you considering using GPR for your commercial or private construction project? Talk to one of our experts today.