Mapping in the Arctic Ocean in Support of a Potential Extended Continental Shelf

Under Article 76 of The United Nations Convention on the Law of the Sea (UNCLOS; U.N. 1997), coastal states may, under certain circumstances, gain sovereign rights over the resources of the seafloor and subsurface of “submerged extensions of their continental margin” beyond the recognized 200 nautical mile (nmi) limit of their Exclusive Economic Zone (EEZ). The establishment of an “extended continental shelf” (ECS) under Article 76 involves the demonstration that the area of the ECS is a “natural prolongation” of a coastal state’s territorial landmass and then the application of a series of formulae and limit lines that are based on determination of the “foot of the slope,” (defined in Article 76 as the maximum change in gradient at it’s base), the underlying sediment thickness, and the locations of the 2500 m isobath and the 350 nmi line from the territorial sea base line. Although the United States has not yet acceded to the UNCLOS, increasing recognition that implementation of Article 76 could confer sovereign rights over large and potentially resource-rich areas of the seabed beyond its current 200 nautical mile (nmi) limit has renewed interest in the potential for accession to the treaty and spurred U.S. efforts to map area of potential “extended continental shelf”

From the Arctic to the Tropics: The U.S. UNCLOS Bathymetric Mapping Program

Since CHC2006, the University of New Hampshire’s Center for Coastal & Ocean Mapping/Joint Hydrographic Center has mapped with multibeam, the bathymetry of an additional ~220,000 km2 of seafloor in areas as diverse as the Arctic, the Northern Marianas of the western Pacific and the Gulf of Mexico. The mapping supports any potential U.S. submission for of extended continental shelves under Article 76 of the United Nations Convention of the Law of the Sea. Consequently, the mapping has concentrated on capturing the complete extent of the 2500-m isobath and the zone where the Article 76-defined foot of the slope exists. In practice, the complete area between ~1500 and ~4500 m water depths is mapped in each region (with the exception of the Arctic Ocean). The data have been collected in conditions that range from harsh Arctic sea ice to the calms of the Philippine Sea tropics. Although, some of the conditions have limited the quality of some of the data, the data quality is generally quite good and geological surprises have been uncovered on each of the cruises

High Resolution Mapping in support of UNCLOS Article 76: Seeing the seafloor with new eyes

Since 2003, the Center for Coastal & Ocean Mapping/Joint Hydrographic Center at the University of New Hampshire (UNH) has been conducting multibeam mapping of many U.S. continental margins in areas where there is a potential for an extended continental shelf as defined under Article 76 of the United Nations Convention on the Law of the Sea. UNH was directed by Congress, through funding by the National Oceanic & Atmospheric Administration, to map the bathymetry in areas in the Arctic Ocean, Bering Sea, Gulf of Alaska, Northwest Atlantic, northern Gulf of Mexico, the Northern Mariana Islands, Kingman Reef and Palmyra Atoll (Fig. 1). The purpose of these surveys is to accurately locate the 2500-m isobath and to collect the bathymetry data required to eventually determine the location of the maximum change in gradient on Figure 1. Locations and year of bathymetry mapping (yellow areas) for U.S. UNCLOS concerns. the continental rises. A total area of about 862,000 km2 has been completed; approximately 250,000 km2 remains to be mapped. The area between the ~1000 and ~4800-m isobaths has been mapped on each of the completed margins. The mapping has been conducted with multibeam echosounders (MBES) that typically collect soundings with a spacing of ~50 m or less in the focused water depths. After each area is mapped, the data are gridded at 100-m spatial resolution although higher resolution is possible in the shallower regions. The depth precision achieved on all of the cruises has been \u3c1% of the water depth and typically has been \u3c0.5% of the water depth, based on cross-line comparisons. Navigation on all of the cruises has been acquired with inertial-aided DGPS using commercial differential corrections that provide 2 position accuracies much better than ±5 m. All of the MBES systems used produce acoustic backscatter as well as bathymetry but the backscatter quality varies among systems and conditions. Table 1 is a summary of the mapping completed and of areas yet to be mapped for bathymetry. The data are all processed at sea by UNH personnel during their collection and the data, grids and views of the processed data are posted on the worldwide web soon after completion of each area. The data, grids and images can be viewed and downloaded at http://ccom.unh.edu/law_of_the_sea.html

Seafloor mapping in the Arctic: support for a potential U.S. extended continental shelf

For the United States, the greatest opportunity for an extended continental shelf under UNCLOS is in the ice-covered regions of the Arctic north of Alaska. Since 2003, CCOM/JHC has been using the icebreaker Healy equipped with a multibeam echosounder, chirp subbottom profiler, and dredges, to map and sample the region of Chukchi Borderland and Alpha-Mendeleev Ridge complex. These data have led to the discovery of several new features, have radically changed our view of the bathymetry and geologic history of the area, and may have important ramifications for the determination of the limits of a U.S. extended continental shelf under Article 76

The limits of spatial resolution achievable using a 30kHz multibeam sonar: model predictions and field results

A Simrad EM300 multibeam sonar was used to attempt to resolve small (-5m high) targets in 450m of water. The targets had previously been surveyed using a deeply towed 59 kHz sidescan sonar. Using multisector active yaw, pitch and roll compensation, together with dynamically altering angular sectors, the sonar is capable of maintaining sounding densities of as tight as 10m spacing in these water depths. This is significantly smaller than the largest dimension of the projected beam footprints (1 6-64m). The observed data suggest that the targets are intermittently resolved. The field results compare well to the output of a numerical model which reproduces the imaging geometry. Possible variations in the imaging geometry are implemented in the model, comparing equiangular and equidistant beam spacings, differing angular sectors and all the different combinations of transmit and receive beam widths that are available for this model of sonar. While amplitude detection is significantly aliased by targets smaller than the across track beam footprint, under conditions where the signal to noise ratio is favorable, phase detection can be used to reduce the minimum size of target observed to about the scale of the across track beam width. Thus having the beam spacing at the scale is justifiable. The phase distortion due to smaller targets, however, is generally averaged out

Interactive 3-D Visualization: A tool for seafloor navigation, exploration, and engineering

Recent years have seen remarkable advances in sonar technology, positioning capabilities, and computer processing power that have revolutionized the way we image the seafloor. The massive amounts of data produced by these systems present many challenges but also offer tremendous opportunities in terms of visualization and analysis. We have developed a suite of interactive 3-D visualization and exploration tools specifically designed to facilitate the interpretation and analysis of very large (10\u27s to 100\u27s of megabytes), complex, multi-component spatial data sets. If properly georeferenced and treated, these complex data sets can be presented in a natural and intuitive manner that allows the integration of multiple components each at their inherent level of resolution and without compromising the quantitative nature of the data. Artificial sun-illumination, shading, and 3-D rendering can be used with digital bathymetric data (DTM\u27s) to form natural looking and easily interpretable, yet quantitative, landscapes. Color can be used to represent depth or other parameters (like backscatter or sediment properties) which can be draped over the DTM, or high resolution imagery can be texture mapped on bathymetric data. When combined with interactive analytical tools, this environment has facilitated the use of multibeam sonar and other data sets in a range of geologic, environmental, fisheries, and engineering applications

Theoretical and Experimental Investigation of High-Latitude Outflow for Ions and Neutrals

The outflow of ions at high latitudes is one mechanism thought to populate the magnetosphere with ionospheric ions [H+, He+, O+]. Computer modeling can give an insight into the mechanisms and rates at which these ions can populate the magnetosphere, but for atomic oxygen the temperature is about 40% lower than measurement. This can be accounted for by the inclusion of a hot O population at a higher temperature, of about 4000K

Mapping a Continental Shelf and Slope in the 1990s: A Tale of Three Multibeams

Increasing societal pressures on the U.S. continental shelves adjacent to dense population centers have brought to light the lack of accurate base maps in these areas. Existing bathymetric maps and random sidescan sonar surveys are either not accurate enough or do not provide the coverage necessary to make policy decisions. Until the mid 1990s, it was not financially prudent nor technically efficient to map the shallow shelves. However, the availability of high-resolution multibeam mapping systems now allow efficient and accurate mapping of the continental margins. In 1996 the U.S. Geological Survey began a large-scale seafloor mapping campaign on the continental shelf and slope adjacent to Los Angeles, CA. The first survey used a Kongsberg Simrad EM1000 (95 kHz). The survey continued in 1998 by mapping the slope and proximal basins from Newport to Long Beach, CA, using a Kongsberg Simrad EM300 (30 kHz). The area was completed in May 1999 by mapping the entire shelf adjacent to Long Beach, CA using an EM3000D (a dual-headed 300-kHz system). The mapping used both INS from the vehicle motion sensor and DGPS to provide position accuracies of ~1 m. All the data were processed in the field in near realtime using software developed at the Univ. of New Brunswick. Because of the different systems used and the range of water depths, the spatial resolution of the processed data varies from \u3c0.5 m on the inner shelf to 8 m on the basin floors. Perspective overviews of backscatter draped over bathymetry reveals a host of geological features unknown to exist in this area. These features include shallow, linear gullys, barchan dunes, small-scale bedforms in shallow troughs, major canyon system complexes, large- and smallscale mass movements, faults, and large areas of outcrop. The effects on sediment transport of man-made features, such as sewer outfall pipes and dredge-disposal fields, are clearly delineated on the new maps. The maps provide the fundamental base maps for studies as varied as those involving benthic habitats, marine disposal sites, sediment transport, and tectonic ma