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
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
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