Ed Ross

Improvements in Upward Looking Sonar-Based Sea-Ice Measurements: A Case Study for 2007 Ice Features in Northumberland Strait, Canada

Scientific and engineering studies of polar and marginal ice zones require detailed information on sea ice thickness and topography. Accurate information on sea ice thickness and topography data is required for basic ice-covered ocean studies and, increasingly, for addressing important navigation-, offshore structure design/safety- and climate change-issues. Since the early 1990s, upward-looking sonar (ULS) instrumentation have been developed and applied to provide under-ice topography data with high horizontal and vertical spatial resolution. Such internal recording ULS instruments, or ice profilers, are typically operated from the seafloor on taut line mooring systems. The ASL Model IPS4 Ice Profiler, which has been widely used in studies of the Arctic Ocean, as well as in numerous seasonal ice zones and in the Southern Ocean, is being upgraded to allow much expanded data storage capacity (from 69 Mbytes to 1-8 Gigabytes) and 16 bit A/D resolution for ice ranges and other parameters. With typical ping rates of 0.5 or 1 Hz, the enhanced capability of the Ice Profiler provides very high resolution measurements of ice keel drafts and the under-ice topography of sea-ice keel features. The Ice Profiler is often used in conjunction with an Acoustic Doppler Current Profiler which provides direct measurements of ice velocity. The combination of high resolution ice draft time series with ice velocities allows for computation of quasi-spatial ice drafts as a function of horizontal distance. The results from the first deployment of an upgraded Ice Profiler, operated just off the Confederation Bridge in Northumberland Strait, from November 2006 to April 2007, are presented and compared with the results of previous sea ice studies at the same location. The much larger onboard data capacity allows for realization of multiple targets for each ping and, on a subsampled basis, offers data on acoustic backscatter returns over the complete water column. This additional information is being analyzed to examine the nature and cause of occasional false target returns. In past measurement campaigns, there have been episodic occurrences of deep targets detected which are not consistent with sea ice features that can be reasonably expected to occur in Northumberland Strait. These features are often associated with occurrences of the largest (spring) tidal currents, leading to the hypothesis that these anomalous targets may be associated with velocity shears in the water column resulting from strong tidal flows past the bridge support structures. Based on these analyses, improvements to the target detection algorithm are being developed and tested.

Upward looking sonar-based measurements of sea ice and waves

With the recent reduction in summertime ice cover in the Arctic Ocean, year-long moored measurement programs require detailed information on sea ice thickness and topography data throughout most of the year, as well as ocean wave measurements during summer periods of major sea-ice retreat. This information is required for basic ice covered ocean studies and, increasingly, for addressing important navigation-, offshore structure design/safety- and climate change-issues. Since the early 1990s, upward looking sonar (ULS) instrumentation have been developed and applied to providing under-ice topography data with high horizontal and vertical spatial resolution. The internal recording ULS instruments, or ice profilers, are typically operated from the seafloor on taut line mooring systems. In the winter of 2007-2008, a new generation of ULS instrumentation was field tested, initially in Northumberland Strait near the Confederation Bridge separating the Canadian provinces of New Brunswick and Prince Edward Island. With typical ping rates of 1 Hz, the enhanced capability of the Ice Profiler provides very high resolution measurements of ice keel drafts and the under-ice topography of sea-ice keel features. The upgrades intrinsic to the ULS instrument feature much expanded data storage capacity (from 69 Mbytes to 1-8 Gigabytes) and 16 bit A/D resolution for ice ranges and other parameters. The offered combination of much increased dynamic range (via the 16 bit A/D converter) combined with the greatly expanded data storage capacity enables the instrument to operate at much lower gain levels. This facility allows extraction of information on the strength of the backscattering associated with sea-ice in contrast to the larger amplitude acoustic returns from open water, as well as detection of multiple targets from each regular 1 Hz ping. The instruments firmware also provides an ocean wave sampling mode in which a 2 Hz ping rate is used, typically over 20 minutes once each hour, from which non-directional wave spectra and wave parameters can be derived in post processing of the raw data. The new firmware allows the user to program the instrument to operate in up to 12 different sampling schemes over the course of the full deployment. For a typical Arctic Ocean deployment, this enables the instrument to be programmed to measure ocean waves in late summer and early autumn, then both waves and sea ice in autumn, sea ice in the winter and spring, sea ice and waves in the late spring and early summer. These features were utilized in the Northumberland Strait deployment, operated from Nov. 2007 to April 2008, to optimally detect the floating ice cover targets of interest, avoiding alternative false or null targets. Results are also presented on the measurement of ocean waves with wave heights of up to 3 m, and the early winter measurement of scattered ice keels in the presence of ocean waves.

Characterization of Hazardous Ice using Spaceborne SAR and Ice Profiling Sonar: Preliminary Results

Ice can pose hazard for operations (e.g., transportation, shipping, offshore oil and gas exploration) and for infrastructure (e.g., ports, pipelines, offshore structures). There is an increasing need for fine scale characterization of hazardous ice conditions. This information is of interest to many stakeholders including government departments and agencies, and the oil and gas industry. Spaceborne Synthetic Aperture Radar (SAR) sensors have demonstrated the viability and cost-effectiveness of near-real-time monitoring of the regional ice conditions. Satellite derived ice information products typically rely on the interpretation of ice analysts or in some cases semi-automated techniques, and cover relatively large areas at coarse resolution. Development of improved data products using high spatial resolution polarimetric RADARSAT-2 datasets (e.g., Fine Quad) is desired for detailed characterization of potentially hazardous ice conditions. Although validation of ice data products is challenging due to limited ground truth data, there are numerous sites throughout the Arctic with many years of continuous measurements of ice conditions obtained using bottom mounted Upward Looking Sonar (ULS) instruments. Using ULS data we have recently developed analytical methods to characterize highly deformed sea ice features including large individual keels, segments of hummocky ice, multi-year ice, and episodes of internal ice stress, which can also serve as validation data for SAR-based analysis. This paper presents an overview of our ongoing work and very preliminary results on hazardous ice characterization using SAR and ULS data. ULS data view from below and SAR data view from above are complementary information sources, and utilizing both is expected to result in better characterization of the ice conditions. During this work, paired SAR and ULS datasets will be generated to allow calibration and validation of algorithms, and methodologies will be developed to utilize these complementary data sources. This project is expected to (1) develop improved methods for fine scale analysis of RADARSAT-2 data; (2) develop enhanced information products generated in the hindcast mode when ULS and RADARSAT-2 are both available; (3) demonstrate potential for RCM (compact polarimetry). Calibrated and validated information products of hazardous ice will be extremely valuable for users who require such information for engineering design, to make management and policy decisions, and to safely perform operations.

Testing of Ice Profiler Sonar (IPS) targets using a logarithmic detector

Upward-looking sonar (ULS) instruments have become the primary source of data for high resolution and long duration measurements of sea ice drafts to support engineering requirements for oil and gas exploration projects, along with long-term scientific studies of the underside of the sea-ice canopy in the Arctic and other ice-infested areas. ASLs Ice Profiler Sonar (IPS) has been widely used to provide continuous accurate measurements for ice draft at a horizontal resolution of 1 m, which enables the measurement of ice thickness values over periods from 1-2 seconds up to several years, as well as detailed characterization of many hundreds to thousands of keel shapes and other ice features. In 2014, an important redesign of the IPS instrument was initiated to provide improved performance of the original instrument developed in the 1990s and last upgraded by ASL Environmental Sciences Inc. in 2007-2008.

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.

Iceberg severity off the east coast of North America in relation to upstream sea ice variability: An update

Earlier examination of strong correlations between mid-winter spatial extents in Davis Strait and large annual variations in the estimated numbers of icebergs passing south of 48°N motivated detailed studies of the origins of variability in iceberg numbers was conducted over twenty years ago [1]. This work established the critical role played by the processes that control the cyclonic movement of the icebergs from their primary West Greenland calving ground to the northern perimeter of Baffin Bay and, subsequently past the coastal shelves of North America. It was demonstrated that the effectiveness of these processes and year to year variations in their timing tended to overwhelm interannual variations in Greenland iceberg calving rates. A major connection between such fluxes and upstream ice extent was established through the effectiveness of extensive pack ice in lowering deterioration and melt rates of freely drifting icebergs during the last, late winter through early summer, segments of their drift trajectories. This role is exercised through the effectiveness of sea ice in lowering the local water temperature and reducing sea state parameters which essentially determine iceberg lifetime in these segments. Comparisons between historical International Ice Patrol (IIP) records of annual south of 48N iceberg numbers and a shorter record (post-1960s) of sea ice extents indicated strong correlations between the former and the January spatial extent of ice in Baffin Bay and Davis Strait north of 67N. Measures of this extent, designated as the Davis Strait ice index (DSII) were subsequently used on their own or with modifications as a basis for early season assessments and apportionments of resources by the IIP and others with interests in East Coast navigation. The iceberg severity off Newfoundland is revisited in the light of several major efforts to document and reorganize East Coast iceberg data-taking and analyses as well as the availability of, roughly, 20 more years of higher quality sea ice and iceberg data. The updated and extended analysis includes assessing impacts of suspected over-counting in early iceberg surveys and access to improved Canadian Ice Service (CIS) digital ice chart data, available from 1971 to the present, which allows better resolution of the sea ice data in marine areas upstream of 48N both in terms of areas of interest and in time. Examination of the 1971-2014 sea ice concentrations in Davis Strait for mid-January reveal that the post 2000 ice extents are consistent with the iceberg numbers being lower than those observed and inferred from the 1980-1999 sea ice concentrations. This extended analysis also discriminates between sea ice types, in particular first year ice vs. the thinner new to young ice categories for regions with three-tenths or more in ice concentration in the DSSII area of interest.