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Feature Article

iRobot Seaglider With Ogive Fairings Supports Antarctic Research
Increased Payload Capacity from Ogive Fairings Enables AUV to Track Krill Biomass Distribution in Weddell Sea

Feature Author
Chris Yahnker, P.E.
Chief Engineer of Maritime Systems
Feature Author
Elizabeth Creed
Principal Applications Engineer of Maritime Systems
iRobot Corp.
Durham, North Carolina

Feature Author
Karen J. Heywood
School of Environmental Sciences
University of East Anglia
Norwich, England

Seaglider, with an ADCP and echosounder installed on board, being prepped for deployment in the Weddell Sea. (Image courtesy of the University of East Anglia)
In January 2012, a team of researchers from institutions in the United Kingdom and the United States set sail to the Weddell Sea to study one of the few places in the world where water becomes dense enough to sink to the bottom of the ocean. Due to interactions with ice shelves, formation of sea ice and cold temperatures, water from the Weddell Sea plays a large role in ocean bottom waters. As the water from the Weddell Sea sinks, it pushes older water toward the surface creating a global 'overturning' circulation. Within this current, many nutrients are brought to the surface, where they become a key factor in support of the global ecosystem. Harsh environmental conditions and remote locations make studying this ecosystem extremely challenging and thus the perfect place to utilize ocean gliders to conduct long-term surveys.

GENTOO (Gliders: Excellent New Tools for Observing the Ocean), a pilot study to contribute towards the best design for the planned Southern Ocean Observing System (SOOS), utilized ocean gliders to autonomously sample the northwestern Weddell Sea for five weeks. For the first time, researchers were able to make extended physical, chemical and biological observations in this region and study the role they play in ocean circulation, climate and ecology.

iRobot Corp. (Bedford, Massachusetts) participated in this research initiative by providing a Seaglider with new, larger ogive fairings carrying prototypes of a Nortek AS (Rud, Norway) glider acoustic Doppler current profiler (ADCP) and an Imagenex (Port Coquitlam, Canada) 853 echosounder for studying krill. iRobot also provided support personnel both on site and stateside to assist in operating and piloting the Seaglider.

Development of Seaglider and Ogive Fairings
Seaglider is constructed of an aluminum pressure hull surrounded by smooth, hydrodynamically shaped fairings that allow seawater to pass between the inner surface of the fairings and outer surface of the pressure hull. Aft of the pressure hull, within the aft fairing, is a flooded volume that houses the glider's buoyancy compensation bladder and various sensor payloads for collecting data.

In 2010, iRobot launched a major redesign of the external fairings to accommodate the greater payloads being requested by researchers. For example, the Nortek current profiler and the Imagenex echosounder carried by Seaglider on the GENTOO cruise would have been impossible without the new, larger ogive fairings due to the size and weight of these devices.

The original Seaglider, developed by the University of Washington with funding from the U.S. Office of Naval Research and the National Science Foundation, had a payload mass of 2 kilograms in water and approximately 3,200 cubic centimeters of payload volume. The newly designed ogive fairings doubled the Seaglider's payload mass to approximately 4 kilograms and increased the payload volume by 650 percent to more than 21,000 cubic centimeters.

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Chris Yahnker, P.E., is the chief engineer for iRobot Corp. Maritime Systems. He has more than 15 years of experience in designing complex electro-mechanical systems. He led the development of the ogive fairings for Seaglider and heads the integration of the Nortek ADCP and Imagenex echosounder.

Elizabeth Creed is a principal applications engineer at iRobot Corp. Maritime Systems. She has bachelor's degrees in biology and electrical engineering and a master's degree in marine science. She has been working with underwater gliders for the past 10 years.

Karen Heywood is a professor of physical oceanography at the University of East Anglia, leading a research group focusing on understanding ocean processes using hydrographic cruises, remote sensing, numerical modeling, tracers, moorings, drifters and Seagliders, particularly in polar oceans. She teaches at an undergraduate and master's level and has supervised some 20 Ph.D. students.

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