Electromagnetic Induction Sounding
of Sea Ice Thickness
AUSTIN KOVACS, DEBORAH DIEMAND,
AND JOHN J. BAYER, JR.
ice thickness, based upon the above findings, as
INTRODUCTION
well as a second field trial of the Flow Research
In a 1990 field study, a hand-held electromag-
processor module.
netic induction sounding instrument with a spe-
cial plug-in data processing module for the re-
mote measurement of sea ice thickness was
evaluated (Kovacs and Morey 1992). The proces-
sor module, used to convert the measured sec-
The primary sensor is the 9-kg man-portable
ondary electromagnetic field in-phase and quadra-
Geonics Ltd., EM-31-D electromagnetic induction
ture phase response to an ice thickness, was found
sounding system (Fig. 1). This device is designed
to be defective. The electromagnetic instrument
to measure the magnitude of the in-phase and
(EMI) would not work after a short period at
quadrature components of the secondary electro-
temperatures below 10C. Indications were that
magnetic field induced in the ground by the
the source of the problem was battery-related.
instrument's 9.8-kHz transmitted (primary) elec-
The EMI was then used without the processor
tromagnetic field (Geonics Ltd. 1984). Since sea
module. In this operation, the instrument was
ice is relatively transparent at this frequency, the
used to measure an apparent conductivity as a
response measured by the instrument is a strong
function of instrument standoff distance above
function of its height above and the conductivity
the seawater. The results showed that a good cor-
of the seawater. Therefore, an accurate measure-
relation existed between the EMI-determined con-
ment of the secondary electromagnetic field re-
ductivity reading and the sea ice thickness. This
sponse and a full solution analysis of the data
led to the conclusion that a simple graph or lookup
table could be used to estimate sea ice thickness
from the conductivity reading. In short, the tech-
nically elaborate processor module built by Flow
Research, Inc. (Echert 1986 and Echert et al. 1989)
was overly sophisticated for the measurement of
undeformed sea ice thickness. This conclusion was
based on the knowledge that the seawater under
winter Arctic pack ice has a relatively uniform
conductivity of about 2.5 S/m and an overriding
influence on the conductivity determined by the
EMI. In addition, because undeformed sea ice is
relatively resistive, it does not have a significant
influence on the EMI's conductivity measurement
(Kovacs and Morey 1992).
Figure 1. EMI instrument shown resting on
This report gives an assessment of a new
lead ice as used in this study.
Geonics processor module for determining sea
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