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RV Mt. Mitchell Advances Science Through Ocean Mapping
Kongsberg Multibeam Echosounders Used for Cable Routes, Nautical Charts and Alaskan King Crab Habitat Research

AUTHOR:

By Megan Gale
Director of Marketing and Business
Development
Global Seas LLC
Seattle, Washington

Oceans cover 71 percent of the Earth’s surface and contain 97 percent of the planet’s water, yet more than 95 percent of the underwater world remains unexplored.

One tool that will help map these unexplored reaches is the multibeam echosounder. NOAA, the National Science Foundation (NSF) and other organizations have taken advantage of significant advances in multibeam echosounders to address longstanding scientific questions about numerous facets of the ocean.

The RV Mt. Mitchell, a 231-foot purpose-built hydrographic research vessel, is one of the only privately owned vessels on the West Coast of the United States permanently equipped with the Kongsberg Maritime AS (Kongsberg, Norway) EM 120 and the EM 710 multibeam echosounders.

These echosounders allow the vessel to serve as a platform for scientists and surveyors conducting ocean research, and they give the vessel a significant role in many key ocean surveys that provide data to physical and biological marine scientists and climatologists. Researchers and survey contractors also use the Mt. Mitchell platform to operate side scan sonars and sub-bottom profilers, to perform cone penetration tests, and to core and collect samples.

The combination of the equipment and the multibeam echosounders offers hydrographers and the scientific community the ability to map areas of the ocean that would otherwise remain unexplored, facilitating the installation of subsea equipment, helping to make ocean navigation safer and improving understanding of the environment.

RV Mt. Mitchell on charter off Diamond Head, Hawaii, in April 2006.
Vessel Specifications
Mt. Mitchell was built in 1967 as a NOAA vessel. It was purchased in 2001 by Mt. Mitchell LLC and is managed by Global Seas LLC.

After the company purchased it, the vessel was renovated, refurbished and retrofitted with new electronics, machinery, and research and safety equipment.

The lower frequency of the 12-kilohertz EM 120 multibeam echosounder gives the vessel state-of-the-art capabilities to perform seabed mapping to full ocean depth with high resolution, coverage and accuracy. The higher frequency of the EM 710 provides better resolution and accuracy for survey depths between three meters below the transducers to approximately 2,000 meters.


Surveying for Cable Routes
Mt. Mitchell was recently chartered to conduct a survey for the University of Washington’s Regional Scale Nodes (RSN) program, the cabled ocean observatory component within the NSF’s Ocean Observatories Initiative.

During this survey, the research team used the echosounders to create seafloor maps of multiple areas of interest off the Oregon and Washington coastlines. Data collected from the survey will be analyzed to help determine the route of the RSN’s 800-kilometer fiber optic cables, which will carry electrical power and telecommunications bandwidth to scientific instruments in the ocean. Following the cable installation in spring 2011, the primary nodes will be deployed and connected to the cable the following year.

With structure completion and full operation targeted for 2014, this cabled underwater research facility will provide a constant stream of data spatially associated with the Juan de Fuca tectonic plate from the ocean, seafloor and subseafloor. The RSN system will also provide real-time data from the ocean floor and water column that can be used to analyze how ocean changes affect essential fish habitats, commercial fishing, acidity, oxygen levels, climate and the environment.

Mt. Mitchell also played a vital role in surveys for multiple telecommunication endeavors. In December 2008 and January 2009, the vessel surveyed the intended route for the 6,300-mile undersea fiber optic Unity Cable System from south of Adak, Alaska, to Japan using the EM 120 and EM 710. The Unity Cable System was designed to meet the increasing demand for connectivity between the United States and Japan and to connect various intra-Asian cable systems.

Previously, in April 2008, Mt. Mitchell completed a survey for the intended route of the Alaska Oregon Network (AKORN) fiber optic cable. This survey spanned from Florence, Oregon, to Homer, Alaska. The AKORN cable was designed to provide high-bandwidth connectivity between the contiguous United States and Alaska.

The intended route of the RSN cable system off the Oregon and Washington coastlines. (Image courtesy of the RSN Program and the Center for Environmental Visualization at the University of Washington)
Navigation Support
The echosounders also aid in mapping surveys that support navigation.

In May 2009, Mt. Mitchell was chartered for NOAA to survey the deepwater portion of Unimak Pass using the EM 710. The highly traveled pass, located between the Bering Sea and the North Pacific Ocean in the Aleutian Islands of Alaska, is one of the great circle routes for large shipping containers and is used by nearly 3,000 ships annually.

Despite frequent use, Unimak Pass had not been surveyed since the early 1900s, and increased traffic is anticipated with the opening of the Northwest Passage route through the Arctic, making it imperative that nautical charts be updated to improve safe navigation.

Although the deepwater portion of the survey was fairly routine, researchers were able to identify the location where the continental shelf rapidly drops off. Data showed that within approximately two miles, the depth of the ocean plunges from 80 meters to 900 meters. Historical nautical charts represent the vicinity of this drop, but the new data revealed that the vertical drop was far steeper than charts indicated. Refined geomorphological data will inform oceanographic modeling and navigation in this important interface of Pacific and Bering Sea waters.


Habitat Research
In June 2009, a consortium of interested parties, including NOAA, used the Mt. Mitchell and its EM 120 and EM 710 to provide bathymetry of Pribilof Canyon in the central Bering Sea for refinement of essential fish habitat information as well as nautical charting purposes, covering depths from approximately 200 to 2,200 meters.

Between June 2 and June 15, Mt. Mitchell collected 2,660 linear nautical miles of mainscheme lines and 215 linear nautical miles of crosslines, for a total of 874 square nautical miles of coverage. Data retrieved from the echosounders revealed an additional arm of the canyon that was previously uncharted.

During the mission, scientists on board examined areas previously surveyed by submarine. Integrating fine-scale geomorphological and substrate information augmented their ongoing biogeographical studies in the canyon.

This research will benefit mariners, the science community and the commercial fishing industry by providing updated information about the bottom of the canyon and reducing the likelihood of gear loss in that area.

Following the Pribilof Canyon research, Mt. Mitchell surveyed selected regions on the shallower Beringian shelf. Researchers spent two full days surveying 52 square nautical miles off the northeastern shores of St. George and St. Paul islands within areas identified by the National Marine Fisheries Service as essential habitat for the king crab.

Habitat surveys had not been conducted in this region since 1986, leaving scientists to question the physical integrity and ecological status of shellhash juvenile rearing habitat after more than 20 years of changing weather patterns and other conditions.

The EM 710 was used during this pilot survey to collect bathymetric and backscatter data to generate new seafloor maps and identify king crab shellhash habitat.

While the survey did not include grab samples or coring, researchers were able to retrospectively ground truth the information and are confident that the data they gathered successfully delineated king crab habitat substrate types. Additional research and data will be collected in the future to further differentiate king crab habitat features within the Pribilof Island area.


Conclusions
The Mt. Mitchell has mapped only a small portion of the ocean, but each discovery makes a significant impact on scientific knowledge, fisheries, safe transit for goods and tourism, communication, Earth systems and the environment. Development of new underwater technology provides a critical research tool for missions by oceanographers and organizations striving to advance the progress of ocean exploration.


References
For a full list of references, please contact Megan Gale at megan.gale@globalseas.com.



Megan Gale is the director of marketing and business development for Global Seas LLC. She recently joined the company and manages inquiries and relations for the RV Mt. Mitchell and all other research vessels owned and operated by Global Seas.


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