Geonics Limited EM31-SH, Operating Manual

Page: 39 / 49

EM31-SH MANUAL Page
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6.6
Example E: Cooksville/Mississauga, Ontario (EM31)
Measurement Interval: 25 feet
This example illustrates a survey carries out with the EM31
to search for a buried river channel. The channel, which is
filled with glacial till, has been cut into the Dundas shale
which, as seen from the example, has a resistivity of the
order of 25 to 30 ohm-meters. The total time to plot out the
profiles shown in the figure was approximately 1½ hours, with
a measurement interval of 25 feet. A shortcoming of the
technique is seen on line 5, where a region was encountered
which was so conductive that it was not possible to take
readings.
The second sheet illustrates the application of the two layer
curves to interpret the survey results in terms of depth.
6.7
Example F: Discontinuous Permafrost (EM31)
Measurement Interval: Variable
These two examples were taken in Northern Canada and compared
the results obtained with the EM31 with a medium frequency
version of the Radiohm (Geonics EM32) technique operating at
250 kHz. The data interval is fairly coarse, nevertheless
there is good agreement between the two techniques, which is
particularly interesting in view of the fact that the current
distribution in the ground is totally different for the two
systems. Furthermore the EM31 operates at frequency of
approximately 9.8 kHz whereas the MF radiohm operates at 250
kHz.