Ground Penetrating Radar (GPR) Imaging
Ground-penetrating radar is analogous to the seismic reflection technique, except that radar (microwaves) are utilized rather than acoustic waves. Radar waves generated at the surface are reflected from subsurface boundaries separating materials of contrasting conductivity and dielectric properties and are returned to the surface. Like seismic reflection, the greater the contrast, the greater the amplitude of the reflection. Data are displayed in time in a manner similar to seismic reflection data. The velocity at which the radar waves travel through a medium is related to the dielectric constant and knowledge of this parameter can allow conversion of a time section to a depth section. Radar waves are transmitted and received by a control unit operating a transducer / antenna that is pulled along the ground. A time section is simultaneously displayed on a chart recorder, allowing the images to be examined during data acquisition. Adjustments in recording parameters can be made as necessary. Effective depth of penetration ranges from about one foot in moist clay to 50 feet or more in dry granular sediments and rocks, and is governed by ground electrical properties. Also, higher frequency signals are attenuated faster then lower frequencies. Several antennae are available so that wave lengths can be matched to target dimensions for optimum imaging.
Search for buried drums.
Void survey in basement.
Across the Axis of an Underground Storage Tank
Along the Axis of an Underground Storage Tank
Former tank pit excavation is found with GPR to guide choice of environmental sample locations.