Ground-penetrating radar

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A ground-penetrating radar data image, generated as part of the search for the head of Yagan within a grave site in Everton Cemetery in 1997.

Ground-penetrating radar (GPR) works much like regular radar, using pulses of electromagnetic radiation in the microwave band (UHF/VHF frequencies) of the radio spectrum, and reading the reflected signal to detect subsurface structures and objects without drilling, probing or otherwise breaking the ground surface. Applications include locating buried voids/cavities, underground storage tanks, sewers, buried foundations, ancient landfills. It can also be used to characterize bedrock, ice, the internal structure of floors/walls, water damage in concrete, and the internal steelwork in concrete.

GPR uses transmitting and receiving antennae. The transmitting antenna radiates short pulses of the high-frequency (usually polarized) radio waves into the ground. When the wave hits a buried object or a boundary with different electrical properties, the receiving antenna records variations in the reflected return signal. The principles involved are similar to reflection seismology, except that electromagnetic energy is used instead of acoustic energy, and the resulting image is relatively easy to interpret.

The range of the scan is affected mostly by the conductivity and composition of the ground; the resolution of the scan is affected by the scanning frequency. Higher frequencies do not penetrate as far as lower frequencies, but give better resolution. Best penetration is achieved in dry sandy soils or massive dry materials such as granite, limestone, and concrete where the depth of penetration is up to 15 meters. In moist and/or clay laden soils and soils with high electrical conductivity, penetration is sometimes less than 1 meter.

Ground-penetrating radar units are generally in contact with the ground for best performance. There are GPR horn antennas that can be used one to two feet above the ground. These antennas can collect data at highway speeds.

Emissions regulation in 2005 European Telecommunications and Standards Institute (ETSI) deemed it necessary to regulate GPR equipment and GPR operators to control excess emissions of electromagnetic radiation. The European GPR association (EuroGPR) was formed as a trade association to represent and protect the legitimate use of GPR in Europe.

A similar technology is wall-penetrating radar, which can read through walls and even act as a motion sensor for police.

Both types of radar are considered ultra wideband. These differ from a metal detector, which uses electromagnetic induction rather than reflection.

The "Mineseeker Project" seeks to design a system to determine whether landmines are present in areas using ultra wideband synthetic aperture radar units mounted on blimps.