Ice Ridge Identification Methods and Analysis of Upward Looking Sonar Data from Fram Strait 2006-2010

摘要

Arctic sea ice pressure ridges are important features both within geophysics and engineering. We present ridge statistics from the Transpolar Drift （TD） where it exits the Arctic Ocean in the Fram Strait, derived from upward looking sonars (ULS) moored on the seabed. The statistics are of interest to those studying the upstream TD, and for oil field developments on the North East Greenland shelf. The nature of the derived ridge statistics depends on which method is applied, and the input parameters. Based on ULS data obtained during the deployment years 2006/07(one instrument), 2008/09 (three instruments) and 2009/10 (one instrument), we have produced and compared probability of exceedance curves using the Rayleigh and the Cutoff method. The effect of varying input parameters like the Threshold value and the Minimum draft were also investigated. The Rayleigh method always produced more ridges than the Cutoff method, when using the same input parameters. The Cutoff method produced deeper keels and would provide more conservative results in a load calculation. When varying the Threshold and Minimum draft parameters the ridges maximum draft at 0.1% exceedance level could vary as much as 4-6 m. At the westernmost sonar 350 ridges passed on average each day during the most extreme month(January 2007). In May and June (2007) about 7 ridges deeper than 15 m drifted over this location each day. The deepest ridge detected in the data set had a draft of 34.5 m. Applying a Threshold value of 2.5 m and a Minimum draft of 5 m, a total number of 232000 ridges were identified in 5 seasons of data.