Ground penetrating
radar (GPR) is a high-resolution geophysical method for imaging shallow
soil and ground structures. GPR is particularly useful for locating
buried objects, disturbed areas, or subsurface void spaces.
Pulses of
high-frequency radio waves are directed into the ground in a conical
beam. At the zone of contact between two layers of rock or soil, the
contrast between the electrical characteristics of the two materials
will reflect the pulses back to
the GPR antenna. The reflected signal is processed to develop a
profile of the soil and rock layers beneath the antenna.
The GPR antenna is
moved along a traverse line to develop a cross-sectional image of the
site's subsurface. Disturbances in the layering can show us the
location of old excavations. Strong local reflections can reveal buried
objects.
Foree & Vann, Inc.
uses a Geophysical Survey
Systems, Inc. SIR-2000 unit, capable of imaging to depths of about
30 feet under typical southwestern soil conditions.
Foree & Vann, Inc. used GPR to locate a disused
underground
storage tank at this communications facility. The stakes seen in the
foreground were used for spatial control points.
