| GEO-GRAF |
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| What Is GPR? -
Geophysical Equipment Descriptions - Electromagnetics |
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| EM
technology is utilized by Geo-Graf to locate and
delineate metallic subsurface targets such as USTs,
drums, utilities, reinforced pads, conductive fill and
other metallic anomalies. |
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| EM
technology works on the following principle. A
transmitter emits a wave and a receiver is tuned to
detect any changes in the wave. If the wave comes in
contact with a metallic object, a current is subsequently
produced on that object by the emitting wave (related to
the theory of loosely coupled transformers). This current
will then slightly distort some of the characteristic
properties of the emitting wave. The receiver will detect
and process the distortion, giving the operator a
relative signal strength indication. Thus, given this
signal strength indication, a trained and skilled
operator is able to delineate the dimensions of the
subsurface target. The EM device used by Geo-Graf
has separable transmitter and receiver. When searching
for buried metallic mass, the transmitter and receiver
are connected via a 4' handle. Unlike RF technologies,
the receiver is not set for detecting the transmitting
signal, it is set in a null position that will only
detect distortions of the emitting signal. Thus, the
slightest distortion in the emitting wave will be
detected. As a result, the relative size and location of
a subsurface metallic target can be detected based on the
“strength” of the distortion. |
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| Detection
of subsurface targets will be hindered only when the soil
or the surface contains conductive material. This only
occurs in instances where metallic fill material was used
or dumped, or over surface reinforced concrete pads. The
only technology capable of detecting targets beneath
reinforced pads is GPR. |
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