The Detection of Multi-Year Ice Using Upward Looking Sonar Data

Upward looking sonar (ULS) instruments on year-long sub-surface moorings are widely used in support of oil and gas exploration programs. The analysis results are used to provide key inputs to the engineering of offshore platform design and ship-based ice management. Detection of the older and harder multi-year sea ice is particularly important for engineering and ice management applications. Here, we analyze multi-year ULS measurements of sea ice in the Beaufort Sea and off Northeast Greenland. The detectability and characterization of multi-year ice is derived from two independent analysis methods. The first method uses the backscattered acoustic pulse shape received by the sonar instrument while the second method involves the degree of the smoothness of the underside of the ice keels away from the leading and trailing edges. Both methods demonstrate skill in detecting multi-year sea ice as distinct from first year sea ice. The two methods are shown to be complementary in that some multiyear ice floes cannot always be clearly categorized by one method alone.