Ground penetrating radar (GPR) uses high frequency electromagnetic waves to acquire subsurface information (ASTM D6432-99).  Energy is radiated downward into the ground from a transmitter and is reflected back to a receiving antenna.  The reflected signals are recorded and produce a continuous cross-sectional “picture” or profile of shallow subsurface conditions.   Reflections of the radar wave occur where there is a change in the dielectric constant or electrical conductivity between two materials.  Changes in conductivity and in dielectric properties are associated with natural hydrogeologic conditions such as bedding, cementation, moisture, clay content, voids and fractures.  Large changes in dielectric properties often exist between geologic materials and man-made structures such as buried utilities or tanks.

Applications

• Ground penetrating radar is primarily used to obtain high resolution cross-sections of natural geologic, hydrogeologic, and anomalous conditions
• Ground penetrating radar is also used for location and evaluation of man-made structures, including location of utilities, rebar in concrete, and non-destructive testing of man-made structures
• Ground penetrating radar has some applications in detecting and mapping contaminant plumes, buried wastes, and drums

Advantages

• Measurements are relatively easy to make
• Ground penetrating radar provides very high lateral and vertical resolution
• Continuous profile measurements are effective for larger surveys
• 2D (horizontal and vertical) cross-sections or 3D models can be obtained
• Often little, if any, processing is required
• The antenna may be pulled by hand or vehicle
• Penetration is commonly less than 30 feet but can be greater than 100 feet in materials having very low conductivity (e.g. freshwater ice)

Limitations

• Depth of penetration is site specific
• Penetration in silts and clays and in materials having conductivity values above 15 to 20 mS/m is limited