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How does GPR work Finding Pipes & Cables Mapping Rebar & Post-Tension Cables in Concrete
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How does GPR work?

In a nutshell, a signal is transmitted from the console, via an antenna, into the ground (or concrete, road, etc).

This signal is reflected from various objects such as earth layering, pipes, cables, rebar, etc.

The reflected signal is captured by the antenna and displayed on the console display in real-time.

How deep can you image?

Ground penetrating radar (GPR) can be used to image from depths as shallow as a few millimeters to as deep as 15-30 metres (under favorable conditions).

In order to image deeper, the physics of the method require that you use lower & lower frequency antennas to transmit the signal, hence the wide range of antennas available. Unfortunately, as with any remote imaging method, the deeper you image, the poorer the resolution.

Some low frequency antennas are not good at resolving small, shallow objects, so the correct antenna for the application should be used.

The good news is that GSSI have developed a dual-frequency antenna: 800MHz for ultra high resolution to approx 1.5-2m and 300MHz for improved depth penetration. This is used in our UtilityScan DF system


What factors affect how deep you can image?

There are a number of factors, but the two most important are:

  • Moisture content - the higher the moisture content, the shallower you will image.

  • Composition of the host (ie the stuff surrounding the target)  - the more conductive the host, the shallower you will image.

Poor environments include wet soils and soils with a high clay content. To overcome this you can try use a lower frequency antenna. This may work, but is not always a solution.

Other factors include ambient noise (spurious electric & radio freq signals), antenna design, transmitter power, and others.

Which antenna should I use?

When you're deciding which antenna to use you need to know how deep you need to image. Use an antenna that will just get down to that depth, with a bit of a "margin of error" built in to your estimate.

For example, if you need to image down to 1.5m to locate pipes & cables, the 400MHz antenna would probably be the best choice.

The higher frequency antennas (900MHz, 10000MHz and higher) would not penetrate deep enough.

The lower frequency antennas (270Mhz, 200MHz and lower) would penetrate deep enough, but you would also have a drop in resolution.


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