GPR, or Ground Penetrating Radar, is a set of instruments that use electromagnetic waves that delineate structures and objects in matter. The technique was developed in the 1970s to map geological structures. Today, we have a very broad range of products designed for specific applications such as concrete investigations, utility detection, borehole investigations and other geophysical measurement.

First, covermeters are based on induction and the assumption of certain rebar sizes, with the ability to solely detect metallic targets one layer thick. Also, the covermeters often provide ambiguous readings when the rebar are too close. The CX systems are able to detect metallic and non-metallic targets as well as voids. In addition, the CX systems can "see through" a rebar mesh to additional layers.

 Different frequencies are required to detect different targets. A higher frequency is necessary to detect a smaller target. The downside to this, though, is that a higher frequency will not penetrate relatively deeply. 

This the most common question asked of ground penetrating radar (GPR) vendors. While the physics are well-known, most people new to GPR do not realize that there are physical fundamental physical limitations.

Many people think GPR penetration is limited by instrumentation. This is true to some extent, however it must be noted that the material in which the target is surrounded or covered by primarily governs exploration depth. No amount of instrumentation improvement will overcome this fundamental physical limit.

Below are general rules of thumbs regarding penetration depths and range resolution: