How accurate is GPR?

Generally, GPR will reveal the horizontal positioning of targets within their exact locations. However, there are numerous of factors that may affect the speed and accuracy of depth measurements. These include soil type and moisture content, among others.

The radar signal velocity depends on the composition of the material being scanned and the depth of the prospective. For instance, the signal will travel slower through soil types that are more challenging to penetrate. Similarly, the depth between the antenna and its target is calculated in line with the period of time that it takes for the radar signal to be reflected from the target and back again to the system.

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The moisture content of the material also affects the velocity of the signal. Though it is usually not possible to learn the exact velocity that the GPR signal travels through the material, it is almost always possible to estimate this within 90% accuracy. It is possible to use a depth to a known object to find out a precise velocity and therefore calibrate the depth calculations. However, this system is only successful when the material has a consistent composition, like concrete.

There's one inescapable limitation, however.  Additional resources  to natural differences in the composition of geological layers, the precise velocity of a signal will vary in one point to the next when investigating underground. There are several techniques for modeling the variations in velocity across the survey path, but they are ultimately estimations and so are not completely precise.