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Ground Penetrating Radar (GPR)
operates like other, more familiar radar systems such as police or weather
radar. A radio frequency signal is transmitted into the earth and reflected
back from interfaces in the path of the signal at which changes in the
electrical properties (dielectric constant) of the subsurface materials occur.
GPR provides a continuous
profile of the subsurface.
GPR allows for the
collection of large amounts of data in a short period of time, making it a
cost-effective method for many projects. GPR is commonly used in
conjunction with other geophysical techniques such as
magnetic,
electromagnetic
induction, and
seismic refraction.
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General Applications |
Specific Applications |
- construction / engineering projects
- environmental audits and site assessments
- evaluation of active / inactive industrial sites
- public / private remedial investigations and feasibility studies
- geological studies
- archaeological studies
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- determine the location, dimensions, and burial depth of drums,
underground storage tanks, and utilities
- locate contaminant plumes
- delineate waste pits, trenches, landfill edges
- determine the location of old foundations
- locate voids in bridge decks, airport runways, dams, and
roadways
- determine water table and bedrock depths
- detect sinkholes in karst terrain
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As the GPR antenna is
moved across the surface, it transmits electromagnetic signals into the
sub-surface and receives reflections which are then amplified, processed,
and displayed in real-time on a graphic recorder and a color video
monitor. The GPR data are also recorded on tape for later playback and
processing.
Experience and equipment are critical in order to derive the full
benefit from the ground penetrating radar technique. At
Hager-Richter, we
have the experience and resources to provide you with reliable guidance
and accurate data.
Experience is crucial in the analysis and interpretation of GPR data, and
especially in evaluating the feasibility of GPR investigations where
site-specific limitations are present.
Our state-of-the-art equipment complements our experience, often overcomes
site limitations, and enhances the quality of our work. We own a full
complement of antennas for different resolutions and exploration depths.
Our color video field monitor allows us to compensate for amplitude
differences and quickly adjust our field procedures to obtain the best
data possible. Our survey wheel automatically triggers the placement of
markers at equal intervals, thereby increasing the accuracy of survey
distances. The processing software we use allows us to modify the way data
are displayed and to filter out extraneous noise, providing us with a
clearer view of subsurface conditions.
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GPR Case Study |
| Problem:
A county airport
authority in a Mid-Atlantic state wished to inventory all
underground storage tanks (USTs), some dating back to World War II,
on airport lands. The objective was to determine whether any tanks
were leaking and possibly contaminating vulnerable aquifers. The
number of tanks was unknown, and the 1,400-acre size of the site
compounded the problem. Solution:
Our client
conducted a historical search that narrowed the areas for
geophysical investigation to about 250 acres, on which over 100
buildings were present. We then completed the surveys in a period of
three months using two geophysical techniques. The first phase of
geophysical investigation was a reconnaissance magnetic survey,
consisting of data collection at over 10,000 stations. In the second
phase, a GPR survey was focused in areas of magnetic anomalies and
near the buildings. Over 140,000 linear feet of GPR profiling
located 57 USTs and documented their dimensions and depth of burial. |
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