Description

Ground Probing Radar (GPR) is a form of radio echo sounding that investigates shallow subsurface features. Short pulses of electromagnetic energy are emitted from a transmitter antenna into the subsurface at frequencies between 10 and 1000 MHz. The technique evaluates the subsequent propagation and reflection of this energy wave in the ground, to produce an image of subsurface conditions. The propagation, velocity and attenuation (signal loss) of the energy wave are dependent on the dielectric properties of the ground, which are primarily controlled by water content. When the radar wave encounters an abrupt change in these properties, a proportion of the signal is reflected. The reflected signal is detected by the receiver antenna and converted for display as a depth profile of signal reflection amplitude against two-way travel time to reflector.

Where electrical properties of the ground change abruptly e.g. from dry to water saturated ground, a strong proportion of the signal is reflected, and the signal continuing through the subsurface is weakened and slowed.

GPR is frequently used in environmental site assessment programs. Environmental site assessment programs regularly need to delineate man-made disturbances and buried materials. GPR can define soil stratigraphy, which provides insight into the subsurface factors controlling prior site development. Objects buried on site such as barrels, containers and old foundations can also be directly detected with GPR. GPR responds to changes in soils condition, compaction and water distribution.

GPR is now used extensively for locating and mapping buried utilities including pipes, cables and conduits as well as route clearing for new installations. GPR is particularly useful for locating non-metallic buried conduits and pipes, which can be very difficult to detect.

Results can be severely degraded by the presence of clay, or by interference from large and irregular surface material, such as cobbles or fill. Penetration is generally limited to a few meters.