As the GPR system is moved across the surface, pulses of electromagnetic energy are directed into the ground from a transmitting antenna. The energy travels though the ground where buried objects reflect/scatter part of the energy back to the surface, which is picked up by the GPR’s receiving antenna. These returning signals are converted in to a GPR section (or radargram) which is displayed on a computer screen in real-time. The operator then uses knowledge, skill and experience to assess the data and interpret the features seen in the section.
| Antenna centre frequency (MHz) | Approximate imaging depth in soil (metres) | Approximate target size in soil (metres) |
| 1500 | 0.3 | 0.03 |
| 1000 | 1 | 0.1 |
| 500 | 2 | 0.2 |
| 250 | 3 | 0.3 |
| 100 | 5 | 0.5 |
| 50 | 10 | 1 |
| 20 | 20 | 2 |
Surveys are usually conducted along profile lines (to produce 2D sections). However, any number of closely spaced lines can be combined to create a 3D volume of data. GPR systems are designed to use different antenna frequencies (typically 20-1500MHz).
Low frequency systems (20-250MHz) penetrate the deepest, but only image larger objects. These tend to be used for hydrological, glacial and geological work. Higher frequency systems (>250MHz) see smaller objects but don’t penetrate as deep. These are more commonly used for civil engineering and NDT applications.
GPR is perfectly safe to use but, as with any site technique, appropriate heath and safety risk assessments must be made before carrying out an investigation. To use a GPR system in the EU, operators need to have an appropriate and up-to-date licence, be adequately trained, responsible and follow a code of practice. Operators must ensure that their surveys do not interfere with any vital telecommunications systems (e.g., aircraft, hospitals, defence, etc).