Todd Mudge

Real-Time Pack Ice Monitoring Systems - Identification of Hazardous Sea Ice Using Upward Looking Sonars for Tactical Support of Offshore Oil and Gas Projects

There is an increasing requirement for real-time detection of sea ice hazards. These hazards include the identification of thick ice keels, large hummocky ice, fast moving ice, rapidly changing ice direction and multi-year ice. Such information is needed in real-time to support tactical applications for safe routing of ships in heavy sea ice concentrations. More recently, a need has emerged for tactical support of offshore oil and gas activities in ice infested waters of the Arctic Ocean and in marginal ice areas such as the Barents Sea, the Sea of Okhotsk, the Caspian Sea, Baffin Bay, the Labrador Sea and East Greenland waters. Reliable upward looking sonar (ULS) instruments, including the ASL Ice Profiler for ice keel measurements and the Acoustic Doppler Current Profiler for Ice Velocity measurements have been widely used in these areas for many years. These instruments, which record data internally, are operated from subsurface moorings that are deployed and recovered by ship during times of minimal sea ice coverage. Providing real-time measurements from the upward looking sonar measurements operating under heavy ice cover pose new technological challenges. The use of surface buoys to relay data from subsurface instruments to shore facilities or satellites is not possible due to the ice cover itself. A more feasible approach is to transmit the data from each instrument using underwater cables on the sea floor and which link the instruments on the subsurface moorings to a bottom mounted or floating structure. For a floating structure, the use of high performance acoustic modems may be required. Previous experience with real-time ULS ice measurement systems dates back to operational projects undertaken from 2002 to the present. More challenging requirements for real-time ULS ice measurement systems are being addressed in much deeper and more remote areas of the Arctic Ocean such as the Barents and Beaufort Seas. Conditions in these areas can vary from short episodes of hazardous ice to more prolonged and severe ice conditions. ULS ice systems may be deployed on a yearround basis or used episodically strategically just before hazardous ice episodes begin. The requirements for timely and accurate ice information demand high reliability in support of ship navigation, offshore oil and gas drilling and development applications. The real-time ULS ice measurement system must be capable of operating for multiple years without servicing in conjunction with other metocean sensors packages (e.g. ice radar, satellite, winds). Multiple ULS measurement arrays will be needed over operational areas spanning distances of many kilometers. For these Arctic Ocean applications, cabled ocean observatory technology and advanced underwater acoustic modems become key enabling technologies. Recent developments of automated detection techniques for deep keels, large hummocky (rubbled) ice, high ice speeds and rapid changes in ice direction derived from data collected from autonomous ULS systems will be described. Robust realtime versions of these algorithms, along with development of automated identification techniques of old-ice using acoustic backscatter data from the Ice Profiling Sonar, will be essential in providing the required tactical ice information.

Estimation and Validation of Floe Size Distribution from Upward Looking Sonars

Moored upward looking sonars (ULS) have been used extensively for over twenty years to measure sea ice dra thicknesses and ice keel widths. They have rarely been used to analyze ice floe sizes. In 2015, Statoil Canada, Arc cNet, the Research & Development Corpora on of Newfoundland and Labrador (RDC) and Husky Energy partnered in an offshore research expedi on, a component of which was Ice Profiler Sonar (IPS) and Acous c Doppler Current Profiler (ADCP) measurements in waters off Newfoundland. This provides an excellent opportunity to develop methods to es mate floe size distribu ons in the marginal ice zone. IPS data is typically analyzed for ice dra and for the presence and absence of sea ice. ADCP bo om tracking data during periods of high ice concentra ons provides direct measurement of ice dri . Deriving these ULS-based parameters in the low concentra ons and o en energe c wave environment of the marginal ice zone is difficult. A six-day period of rela vely low wave energies was analyzed for ULS derived ice floe sizes. Over 1000 floes were detected with most of the detected widths being less than 30 m and a peak in the distribu on at less than 10 m. Ice concentra ons and ice dri s as derived from the ULS were similar to those reported by Canadian Ice Service daily ice charts. Analysis of both theore cal and natural ice floe shapes suggests that the average of the ULS determined ice floe widths is typically about 70 to 80% of the equivalent diameter and about 55% of the typical maximum horizontal extent. Thus, much of the ULS detected floes were likely smaller than the resolu on of satellite imagery. As the ULS moorings measure ice dra every one or two seconds and ice speeds every one minute, es mates of average floe mass, momentum and energy of ice features observed during the six-day analysis episode were possible. Contact Informa on Todd Mudge ASL Environmental Sciences Inc. 1-6703 Rajpur Place Victoria, B.C. V8M 1Z5 Canada m: +1-778-977-3385 | t: +1-250-656-0177 x 116 | f: +1-250-656-2162 e: | w: tmudge@aslenv.com www.aslenv.com Estimation and Validation of Floe Size Distribution from Upward Looking Sonars Todd Mudge; Keath Borg; Kaan Ersahin; Ed Ross; Dawn Sadowy; Jessy Barrette; Nikola Milutinovic. ASL Environmental Sciences Inc., Victoria, BC, Canada.