Estimating sea ice coverage, draft, and velocity in Marguerite Bay (Antarctica) using a subsurface moored upward-looking acoustic
Doppler current profiler (ADCP)
Jason Hyatt1,2, Martin Visbeck3,
Robert C. Beardsley1, and W. Brechner
Owens1
1Department of Physical Oceanography, Woods Hole
Oceanographic Institution, Woods Hole, MA 02543
2Science and Mathematics Department, Massachusetts Maritime
Academy, Buzzards Bay, MA 02532 email: jhyatt@maritime.edu
3Leibniz-Institut fuer Meereswissenschaften
(IFM-GEOMAR), Duesternbrooker Weg
20, 24105 Kiel, Germany
ABSTRACT
A technique for the analysis of
data from a subsurface moored upward-looking acoustic Doppler current profiler
(ADCP) to determine ice coverage, draft and velocity is presented and applied
to data collected in Marguerite Bay on the western Antarctic
Peninsula shelf. This
method provides sea ice information when no dedicated upward-looking sonar
(ULS) data is available. Ice detection
is accomplished using windowed variances of ADCP vertical velocity, vertical
error velocity, and surface horizontal speed.
ADCP signal correlation and backscatter intensity were poor indicators
of the presence of ice at this site. Ice
draft is estimated using a combination of ADCP backscatter data, atmospheric
and oceanic pressure data, and information about the thermal stratification. This estimate requires corrections to the
ADCP-derived range for instrument tilt and sound speed profile. Uncertainties of 0.20 m during midwinter and
0.40 m when the base of the surface mixed layer is above the ADCP for ice draft
are estimated based on (a) a Monte Carlo simulation, (b) uncertainty in the
sound speed correction, and (c) performance of the zero-draft estimate during
times of known open water. Ice velocity
is taken as the ADCP horizontal velocity in the depth bin specified by the
range estimate.
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