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Gliding in the Gulf


Gliding in the Gulf
An autonomous underwater device named Nemo will provide ocean scientists with detailed deep-sea data

About the Photo: Mary Jane Perry, a professor of marine sciences and oceanography at the University of Maine's Darling Marine Center, is a pioneer in the use of autonomous underwater gliders for remote research. In June, she deployed the first such glider in the Gulf of Maine with the help of UMaine colleagues Neal Pettigrew and David Townsend. In this photo, Rob Bell and the crew from the R/V Cape Hatteras retrieve Nemo after its first mission.

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With its bright yellow wings, a battery of sensors and seemingly endless endurance, the latest technological tool being employed by marine researcher Mary Jane Perry is offering scientists a glimpse of the unknown as it slowly cruises the coast of Maine.

In June, the University of Maine's first glider of this kind was deployed into the chilly waters of the Gulf of Maine. Affectionately dubbed Nemo, the 6-foot, fluorescent yellow device promises to change the way we look at ocean ecosystems.

Autonomous gliders like Nemo represent a whole new way of carrying out ocean research. Looking like a cross between a torpedo and a manta ray, gliders are built for long-distance, low-energy travel. On its first voyage along the Maine Coastal Current, Nemo cruised along at just under 1 mile per hour, its multiple environmental sensors whirring away 24 hours per day, seven days a week. The glider's data-gathering marathon continued for two weeks less than half of its monthlong excursion capability.

"One of the main advantages of gliders is their persistent presence in the ocean," said Perry, a professor of marine sciences and oceanography at UMaine's Darling Marine Center and a pioneer in the use of autonomous underwater gliders for remote research, speaking in a presentation to colleagues in July. "They give us the ability to gather data and observe features over time that might never be observed using satellites or other platforms.  If you have to wait for a ship, you might entirely miss an important event."

Nemo's ability to operate for an entire month at a time is due in part to its unique method of movement. Using an internal piston that alternately draws in and expels seawater from a chamber in the rear of its tubular housing, Nemo changes its buoyancy by shifting the ratio of internal seawater to oil, which is stored in a bladder in the nose of the device. The buoyancy changes are translated into forward motion with the help of its wings.

Nemo's rhythmic rise and fall propels it, albeit slowly, through the water column. At set intervals, it rises to the surface, transmitting data back to the lab on such features as phytoplankton concentration and salinity. It maintains a predetermined course by checking its position via GPS or accepts new instructions from researchers working from a ship's cabin or mainland lab.

The 100-pound glider's sensors must be small and durable enough to operate effectively inside the device. Perry has been instrumental in facilitating the creation of glider-friendly sensors since she began working with the devices nearly 10 years ago at the University of Washington.

"Part of my contribution to get the program going came through cooperating with industry to create smaller sensors. Together, we were able to reduce optical sensors from the size of a football to the size of a hockey puck, which is a significant improvement when you consider the size and weight limitations on a glider," says Perry.

Nemo comes equipped with multiple optical sensors that capture both backscatter and fluorescence. Other sensors deliver a stream of data on water temperature, salinity and oxygen content. With the ability to glide along at depths of up to 200 meters, Nemo can gather and transmit a broad range of data that fixed sensors and satellites simply can't provide.

Perry's goal is to have two or more gliders operating in Maine waters, allowing researchers to maintain a constant stream of data by replacing the autonomous devices on a monthly basis. With funding from the Office of Naval Research and the UMaine Office of the Vice President for Research, Perry worked closely with School of Marine Sciences researchers Neal Pettigrew, David Townsend and Carol Janzen to acquire Nemo and initiate what they hope will become a long-term program of research utilizing multiple gliders.

Perry is using the data gathered during Nemo's first foray into the Gulf of Maine to examine the relationship between salinity, dissolved organic matter and phytoplankton in the water column. She hopes to use the data to better understand how the distribution of plankton is affected by climate variability. However, the current project only hints at the level of scientific insight that Nemo and gliders like it could one day provide.

Perry envisions future data-gathering missions that will serve the needs of multiple researchers, contributing reliable information that can be used in conjunction with satellite imagery, fixed sensor arrays like the Gulf of Maine Ocean Observing System (GoMOOS) and other data platforms to create a more accurate picture of the forces at work beneath the waves.

 "Each platform has its advantages and its biases. A combination of platforms is needed to give a true picture in a turbulent fluid like the ocean," says Perry. "For instance, a glider can see the subduction of plankton where a satellite can only see the surface. It can help to fill in the blanks by putting together a more four-dimensional picture in terms of space and time."

As interest in the data-gathering potential of gliders gains momentum, Perry hopes to develop a backbone of support for ongoing glider missions. She also plans to foster the educational potential of the device by using glider research missions as teaching and training opportunities for students.

"This is definitely the way oceanography is going," says Perry. "It's an incredible way to look at the ocean. Every time you look, you learn something new."

By David Munson
November-December, 2006

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