What is ground penetrating radar?
Ground-penetrating radar (GPR) is a non-destructive method that uses radar pulses to image the subsurface. It is a geophysical method that uses electromagnetic radiation in the microwave band of the radio spectrum, and finds out the reflected signals from subsurface structures.
Ground-penetrating radar uses transmitting and receiving antennas or a system that has both the functions. The transmitting antenna releases short pulses of the high-frequency radio waves, which are usually polarized, into the ground. The receiving antenna records variations in the reflected return signal when the wave hits a buried object or a boundary with different dielectric constants. Except that electromagnetic energy is used instead of acoustic energy, and reflections appear at boundaries with different dielectric constants instead of acoustic impedances, the principles involved in GPR are similar. Ground-penetrating radar can be used in various media, such as soil, rock, fresh water, ice, structures and pavements. It can find objects, changes in material, and voids and cracks.
The maximum depth penetration is found in ice where the depth of penetration can be achieved in several hundred meters. In dry sandy soils and massive dry materials which include limestone, concrete and granite where the depth of penetration could be around 15 meters, good penetration can be found. While in the case of clay-laden and/or moist soils with high electrical conductivity, penetration is sometimes only a few centimeters.
The level of depth of GPR is limited by the electrical conductivity of the ground, the transmitted center frequency and the radiated power. As the conductivity increases, the penetration depth also decreases. One of the other main applications for ground penetration radars is to find out underground utilities. It will be able to generate 3D underground images of pipes, sewage, water mains and power.
Generally ground-penetrating radar antennas are in contact with the ground for the strongest signal strength. The GPR air launched antennas can also be used above the ground. Within the field of hydro-geophysics the cross borehole GPR was developed to be a valuable means of assessing the presence and amount of soil water.
Ground-penetrating radar has various applications in a number of fields. It is used in the field of Earth sciences, and also used to study bedrock, groundwater, ice, and soils. In the field of engineering GPR is applied in locating buried structures and utility lines, studying soils and bedrock, and nondestructive testing (NDT) of structures and pavements.
GPR in the field of environmental remediation is used to contaminant plumes; define landfills and other remediation sites. In the field of archaeology, GPR is used for mapping cemeteries and archaeological features. In the field of law enforcement, GPR is used to locate buried evidences and clandestine graves.
GPR in military applications include detection of unexploded ordnance, mines and tunnels. GPR is also used in borehole radars to map the structures from a borehole in underground mining applications and modern directional borehole radar systems can produce three-dimensional images from measurements in a single borehole.