How does a GPR work?

Ground Penetrating Radars have a ton of applications ranging from construction, utility detection and maintenance to archaeology and even mining.

The first patent of a GPR was filed all the way back in 1910, but it wasn’t until the 70’s that the development and refining of these systems really started to kick off — driven by military research, as is often the case.

But what exactly is a Ground Penetrating Radar and how does it work?

Simply put, the GPR works like any other radar. Waves are pulsed into different materials (concrete, sand etc.) at a specific frequency. The reflection of what the waves bounce off produces an image that tells the user what’s underneath.

The images are often in the form of peaks and hyperbolas, which determine the exact location of the buried objects. Respectively, if there’s no object for the waves to reflect off, they’ll just gradually fade away. The time it takes for the pulse to travel to the target and come back to the radar indicates how deep the object is located.

But how deep can you detect an object?, I hear you asking. That depends on two things —the material under the surface and the frequency of the GPR antenna.

For example, if your goal is to locate rebars or conduits in a concrete environment, you’d need a GPR system with higher frequency, say 1000 MHz. This will allow for a higher resolution image and will reach a depth of around 0.5 metres. If you need to see deeper underground in soil, you’d need a lower frequency (12.5 MHz to 500 MHz).

The distance the wave will travel in a specific material depends on its electric conductivity or also known as a dielectric property. The higher the dielectric number, the more difficult it is for the GPR wave to penetrate. For example, air has a dielectric constant of 1, while water has a constant of about 80.

Things started getting a bit too physics-y, so let’s back off a bit.

As you can see, using a GPR system is an effective and practical way to find out what hides beneath the surface in a nondestructive manner. This saves both time and resources, which is why we can nowadays see such a wide range of applications for these devices.

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