Measurement of Sea-ice draft using upward-looking ADCP on an autonomous underwater vehicle

Abstract During March 2003, Autosub, an autonomous underwater vehicle (AUV) operated by the UK National Oceanography Centre, Southampton, was deployed under Sea ice north of Thurston Island, Amundsen Sea, Antarctica (at ∽71˚ S, 100˚ W). The vehicle was fitted with an upward-looking 300 kHz acoustic Doppler current profiler (ADCP) to provide current velocity above the AUV. The ADCP also recorded ranges to the ocean–ice interface. Such data can be used to derive Sea-ice draft by using a number of novel processing Steps Such as correcting for the coordinate Systems of the ADCP unit and the vehicle as well as corrections for changes in Sound Speed. This paper outlines the processing Stages required to obtain a probability density function (PDF) of Sea-ice draft and presents PDFs for the region north of Thurston Island. The distribution of ice draft was found to be unimodal, with modes between 2.2 and 2.4 m. Given the uncertainty in Sound Speed, the limit of accuracy was estimated as ∽6 cm.

[1]  D. Rothrock,et al.  Thinning of the Arctic sea‐ice cover , 1999 .

[2]  A. Worby,et al.  Observing Antarctic sea ice : a practical guide for conducting sea ice observations from vessels operating in the Antarctic pack ice , 1999 .

[3]  Robert J. Urick,et al.  Principles of underwater sound , 1975 .

[4]  I. Allison,et al.  Seasonal development of the sea-ice thickness distribution in East Antarctica: measurements from upward-looking sonar , 2001, Annals of Glaciology.

[5]  Claude C. Leroy.  Erratum: “Depth-pressure relationships in the oceans and seas” [J. Acoust. Soc. Am. 103(3), 1346–1352 (1998)] , 2007 .

[6]  Frederick Armstrong,et al.  Antarctic Krill Under Sea Ice: Elevated Abundance in a Narrow Band Just South of Ice Edge , 2002, Science.

[7]  Sea surface conditions remotely sensed by upward-looking ADCPs , 1995 .

[8]  Gwyn Griffiths,et al.  Versatile autonomous submersibles - the realising and testing of a practical vehicle , 1998 .

[9]  Neil Peacock,et al.  High interannual variability of sea ice thickness in the Arctic region , 2003, Nature.

[10]  R. Gordon.  Principles of Operation A Practical Primer , 1996 .

[11]  V. Strass,et al.  Measuring sea ice draft and coverage with moored upward looking sonars , 1998 .

[12]  Stephen F. Ackley,et al.  The ice thickness distribution across the Atlantic sector of the Antarctic Ocean in midwinter , 1987 .

[13]  L. Talley,et al.  Ice-Draft Profiling from Bottom-Mounted ADCP Data , 2005 .

[14]  Christian Haas,et al.  Evaluation of ship-based electromagnetic-inductive thickness measurements of summer sea-ice in the Bellingshausen and Amundsen Seas, Antarctica , 1998 .

[15]  C. Leroy.  Development of Simple Equations for Accurate and More Realistic Calculation of the Speed of Sound in Seawater , 1969 .

[16]  Claude C. Leroy,et al.  Depth-pressure relationships in the oceans and seas , 1998 .