Measurements of ice parameters in the Beaufort Sea using the Nortek AWAC acoustic Doppler current profiler

Measurements of sea ice presence, ice keel draft, and ice thickness are important for climate studies and engineering design and maintenance of coastal and offshore structures. Building on the success of upward looking sonar systems for ice measurements, Nortek recently introduced new firmware and measurement methods to make observations of sea ice with the Nortek AWAC acoustic Doppler current profiler. The AWAC employs a dedicated, narrow, upward looking vertical transducer to acoustically measure waves (summer) and ice (winter). One of the first commercial applications of this new measurement capability was a project in 2008 to measure ice parameters in support of the design of an offshore structure and its ice armoring system in the Beaufort Sea, Alaska. An analysis of instrumental and environmental error is described. The AWAC ice measurements are compared to a co-located ASL ice profiler and show a mean difference of less than 0.05 m. Ice formation began in mid-October when air temperatures were routinely below -10° C. The thickness increased almost linearly until it peaked in mid-May at about 1.8 m. This represents an increase in ice thickness of approximately 0.01 m/day. The near-surface current velocity from the Nortek AWAC was used to estimate the horizontal length scales and the direction of movement of mobile ice blocks.