Ground Penetrating Radar Technique:

Ground penetrating radar (GPR) sends out an electromagnetic pulse which is reflected from a "target" and returns to the receiver. The reflected pulse can be used to image buried objects and stratigraphy at shallow depths, providing continuous, real-time profiles of the subsurface.

GPR can be very useful in locating underground storage tanks, pipes, utilities, trenches, and other buried materials. For stratigraphic mapping, GPR can be used to map fill boundaries, shallow bedrock, and other shallow stratigraphy. GPR is also used in archeological and forensic investigations. Using higher frequency (shorter wavelength) antennas, GPR applications include pavement inspection, concrete thickness , rebar inspections and mapping voids beneath pavement or concrete slabs. Borehole and crosshole antennas are also available.

Ground penetrating radar, like other radar techniques, utilizes an electromagnetic (radio wave or microwave) pulses. The electromagnetic pulse is of a lower frequency (80-500 MHz) than other radar, to obtain better penetration in the earth materials. The electromagnetic pulse is sent into the earth and is reflected from the subsurface. This reflection is detected by the GPR antenna and shows the location and shape of the subsurface objects and features. The antenna is pulled slowly along the ground surface to produce a continuous subsurface profile.

Above are some examples of common GPR profiles. The vertical scale is a time scale, giving the time for the radar pulse to travel down to the reflector and return to the antenna. Knowing the pulse velocity in the soils, the travel time can be converted to depth. The horizontal scale corresponds to distance . The profile on the left displays the edge of an excavation. The profile on the right is a non-metallic utility line.