Ground-penetrating radar

Ground-penetrating radar 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, the internal structure of floors/walls, water damage in concrete, and the internal steelwork in concrete.

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.

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. Also see GSSI - www.geophysical.com

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.