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Fluxgate Gradiometer
Fluxgate gradiometers have been developed specially
for the detection of buried archaeological remains. The instrument
measures the local vertical gradient field by using two fluxgate sensors
0.5m or 1m apart. They have been in use since the mid 1970s and are now
used routinely in archaeological evaluation. The instrument is extremely
sensitive being able to detect changes as small as 0.5nT.
The gradiometer can be used for both "scanning" and
detailed recorded survey. The former method involves traversing the site
along regularly spaced linear transects (usually about 10m apart) and
observing the fluctuations in magnetic signal. It enables a rapid
initial assessment of large sites and identification of areas of
potential interest which can then be investigated in more detail.
Collection of detailed data is speedy and with the introduction of dual
sensor instruments, up to 3ha can be investigated in one day with
readings being taken at 1m by 0.25m intervals. The results of the survey
are known while still in the field.
The interpretation of fluxgate gradiometer data can be used to position
excavations in the "best" place, or even to re-design proposed
developments, thereby reducing excavation costs.
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Relatively new
to the archaeological market is the use of a cart system which can hold
a multi-array of sensors, with attached GPS, therefore limited grid is
needed, speeding up the process of data collection. A large area,
free from physical obstructions, is most suitable
for this technique to work at its full potential.
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The advantages of speed and field
display make this technique useful in disciplines other than
archaeology. The range (sensitivity) of the instrument can be adjusted
to make it more suitable for the detection of large ferrous objects and
it can also be used to locate certain natural features.
Sites suitable for Fluxgate
Gradiometry
Any rural or semi-urban site free of excessive surface ferrous material
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Archaeological Targets Detected
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Other Targets Detected
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