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.
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Search for buried drums.
Void survey in basement.
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