Measurements of sea ice properties using a moored
upward-looking acoustic Doppler current profiler (ADCP)
J. Hyatt#, M. Visbeck$,
R. Beardsley#, W.B. Owens#
#Woods Hole Oceanographic Institution, Department of Physical Oceanography, Woods Hole, MA 02543 jhyatt@whoi.edu
$Leibniz-Institut fuer Meerewissenschaften
(IFM-GEOMAR)
ABSTRACT
A technique for the analysis of data from a moored upward-looking acoustic Doppler current profiler (ADCP) to determine ice coverage, draft and velocity is presented and applied to data collected 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 with the ADCP using windowed variances of ADCP vertical velocity and error velocity, and surface horizontal speed. We found signal correlation and backscatter intensity to be poor indicators of the presence of ice at this site. Ice draft is estimated using a combination of ADCP backscatter data, atmospheric and oceanic pressures, and information about the thermal stratification. This estimate requires corrections to the ADCP-derived range of instrument tilt and sound speed profile. Uncertainties of ±0.20 m during midwinter and ±0.40 m when the base of the 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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