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Magnetic surveying is ideal for both reconnaissance and focused surveys. It is
expedient and cost effective, covers more ground in less time, and requires a
minimum of field support. The portability of the instruments makes magnetic
surveying well suited to sites with topographic variations.
Magnetic surveys measure the earth's magnetic field very accurately. Buried
ferrous materials, and in some cases, changes in bedrock lithology, produce
disturbances in the local magnetic field that can be readily detected by
magnetic surveys.
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General Applications |
Specific Applications |
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locate buried ferrous metal objects, including
drums, underground storage tanks, ordnance, and utilities
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locate fractures and faults in bedrock to aid in
the placement of high-yield water wells
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locate buried mafic dikes
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Station measurements are collected and digitally recorded in the field. While
the survey data are collected, a nearby base station automatically records data
to track the diurnal variation in the earth's magnetic field.
As with any survey technique, magnetic surveys have certain limitations.
Overhead and underground utilities, fences, and buildings may interfere with
the collection of accurate data. Our experience allows us to advise you on the
suitability of the magnetic survey technique for specific projects.
The accuracy and thoroughness of our magnetic surveys are enhanced by
our state-of-the-art field equipment. We use microprocessor-controlled
cesium vapor and/or proton precession magnetometers that measure both
total magnetic field strength and the vertical magnetic gradient. The
gradient data help us discriminate near surface objects from objects that
are more deeply buried. We use one magnetometer as a dedicated base
station to ensure the accuracy of the field data collected with the survey
magnetometer. We use the base station data to correct for diurnal
variation of the earth's magnetic field and to detect magnetic storms.
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Magnetics Case Study |
Problem:
A Superfund site in southern New Hampshire was suspected to contain
buried drums containing hazardous wastes.
Solution:
We first conducted a
magnetic survey on a 10' x 10' grid to determine the location of
buried ferrous metal. Our client used the magnetic anomaly maps that
we produced to guide the excavation of the objects, and found over
200 steel drums stacked in trenches. Following the excavation, we
conducted another magnetic survey to document that all of the drums
had been found and removed. |
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