Ground Penetrating Radar (GPR)

Ground-penetrating radar (GPR) is a high-frequency electromagnetic method commonly applied to a number of engineering and environmental problems.

A GPR system radiates short pulses of high-frequency EM energy into the ground from a transmitting antenna. This EM wave propagates into the ground at a velocity that is related to the electrical properties of subsurface materials (specifically, the materials relative dielectric permittivity). When this wave encounters the interface of two materials having different dielectric properties (i.e., soil and water), a portion of the energy is reflected back to the surface, where it is detected by a receiver antenna and transmitted to a control unit for processing and display. 

Depth penetration is a function of antenna frequency and the electrical conductivity of the soils in the survey area. Lower frequency antennas achieve greater depth penetration than higher frequency antennas, but have poorer spatial resolution. Conductive soils, such as clays, attenuate the radar waves much more rapidly than resistive soils such as dry sand and resistive rock.

The GPR method is used for very rapid, high resolution mapping of the shallow subsurface to:

• Locate and delineate underground storage tanks (metallic and nonmetallic)
• Locate metallic and nonmetallic pipes and utility cables
• Map rebar in concrete structure
• Map landfill boundaries
• Delineate pits and trenches containing metallic and nonmetallic debris
• Delineate leach fields and industrial cribs
• Delineate previously excavated and backfilled areas
• Map shallow groundwater tables
• Map shallow soil stratigraphy
• Map shallow bedrock topography
• Map subsurface voids and cavities
• Characterize archaeological sites