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The measurement of the earth’s horizontal magnetic gradient is
particularly useful for detecting near surface magnetic sources.
Exceptionally good gradiometer data can gathered by flying slowly at
very low altitudes. This is an ideal tool for kimberlite exploration.
Terraquest was one of the first survey contractors to operate a
commercial horizontal gradient system as early as 1989.
On a survey of an Alberta kimberlite, utilizing the
Cessna 206 platform equipped with the Horizontal Gradiometer (HG)
system, the colour plot below, shows:
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Horizontal Gradient Vectors that pinpoint the
correct location of the kimberlite between the flight lines.
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The single sensor mag is used to measure the
Total Magnetic Intensity (TMI) shown as the colour image erroneously
shows the kimberlite centered on the flight path
The Horizontal Gradient Systems
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Three cesium vapour sensors, mounted on extensions from each wing tip
and tail
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0.005 nT sensitivity recording at 10 to 20 times per second
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< +/- 0.02 nT fourth difference noise envelope
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AGIS and SDAS fully integrated data acquisition systems
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Real time corrected GPS
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Digital video flight path confirmation at 1/10 second with fiducial
and GPS location registration over print.
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Radar and Barometric altimeters data recorded
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Same day printed profiles of user selected scales and lay out
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Next day infield colour contour plots
Benefits
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Primary advantage in improving, gridding and contouring of data for
enhanced resolution
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Measured Horizontal Gradient data is useful in identifying:
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The precise location of small anomalies between flight lines
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The precise location of contacts, dykes and
faults
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“Magnetic axis” within many of the magnetic units.
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The indication of the dip of some magnetic units
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The discrimination between cultural and small geological sources such
as Kimberlite.
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