the survey line. The conductivity measurements
are shown in Figure 5. The regression curve shown
passing through the data indicates that the con-
ductivity normal and parallel to the line has a
slight bias. This bias indicates that the ice was
slightly thicker parallel to the line. The EMI con-
ductivity readings vs. ice thickness are shown in
Figure 6. As expected, these results show an ex-
ponential decrease in conductivity with increas-
ing ice thickness. The slope of the curve passing
through the data becomes rather small beyond
about 5 m, suggesting that the instrument's reli-
able sounding limit has been reached.
The EMI thickness determinations made paral-
lel vs. perpendicular to the survey line are shown
in Figure 7. As expected from the conductivity
measurements, the ice thickness results indicate
the ice parallel to the line was about 23 cm thicker
than perpendicular to the line. However, no drill
hole measurements were made to confirm this
apparent thickness variation. Possibly that the
small conductivity and therefore ice thickness
variation were caused by ice structure effects.
Kovacs and Morey (1978) showed that currents
under the Beaufort Sea pack ice induce selective
ice platelet growth in which the c-axis of the sea
Figure 4. Aerial view of ~1.0-km-long survey line. The
ice crystals become aligned with the current. This
finding was verified in an extensive field study
line extends from multiyear sea ice, in the foreground, to
by Weeks and Gow (1979). The significance of
first-year sea ice in the background. The dark spot to the
this alignment is that it renders the ice anisotro-
right of the survey line is the shadow of the helicopter
pic and thus affects the electromagnetic (Kovacs
from which the photo was taken.
Figure 5. EMI conductivity reading vs. instrument boom orientation (parallel
vs. perpendicular) to the survey line.
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