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THE ASTORIAN • SATURDAY, DECEMBER 7, 2019
Robot records sounds
of underwater life
along Pacifi c Coast
can only sample at individual locations and
depths.
Gliders with hydrophones have not been
For 18 days, an underwater robot dived used for extensive noise monitoring before,
and surfaced and dived and surfaced — largely because the vehicles’ rudders often
some 402 times in all — listening to the interrupt recordings. Haxel and other sci-
ocean’s depths as it traveled hundreds of entists managed to fi lter rudder noise from
miles along the continental shelf off the their audio using computer algorithms.
Washington state and Oregon coastline.
“I have not seen anybody do an ambient
The torpedo-shaped robot, called a noise study with gliders like this before,”
glider, captured the percussive roar of a said Elizabeth Küsel, a senior scientist with
research ship’s air gun, which reverberated JASCO Applied Sciences, who has worked
like a muffl ed bass drum. It listened to what with gliders for about a decade and was not
sounded like the churn of a wobbly wash- involved in this research. “Their work is
ing machine, which indicated the presence very valuable.”
of a ship passing nearby. The 120-pound
Research scientists launched the glider
robot even caught the delightful, baritone on July 20, 2012, off Grays Harbor, Wash-
whining of humpback whales.
ington. It arrived two and a half weeks later
For years, scientists have been working near Brookings, some 285 miles away.
to untangle the mysteries of ocean sound.
The robot traveled, on average, less than
Noise travels much farther underwater than 1 mph. Its median dive depth was more
it does in air.
than 2,050 feet below the ocean’s surface.
“Sound is to marine animals what light
Scientists recorded throughout its jour-
is to people on land,” said Joe Haxel, an ney, capturing audio of at least 11 encoun-
assistant professor at Oregon State Uni- ters with Pacifi c white-sided dolphins,
versity in marine resources studies. It is three brushes with humpback whales and
the medium through which these creatures several other creatures scientists could not
hear, locate themselves and communicate.
identify.
Just how noisy is the
The robot also cap-
sea? Are humans — with
tured passing vessels and
freight ships and ocean
the powerful air gun of a
‘THIS IS A NEW
drilling and sonar testing
National Science Foun-
WAY TO MAKE
— making it louder?
dation ship conducting
“We know so little
research off the
MEASUREMENTS seismic
about the overall noise in
coast.
the ocean and how that
“It’s basically an
THAT INFORM
affects things — the crit-
explosion,” Haxel said
US ABOUT
ters that live there,” said
of the air gun’s blasts.
Chris Meinig, the direc-
“Every 20 or 30 sec-
WHAT’S GOING
tor of engineering for
onds you’re getting a
ON OUT THERE.’ large rumble in the water
the National Oceanic and
Atmospheric Adminis-
column.”
Joe Haxel | assistant professor
tration’s Pacifi c Marine
Oil and gas compa-
at Oregon State University in
Environmental Labora-
nies also use seismic air
marine resources studies
tory in Seattle.
guns to research possible
A new research paper,
deposits. Their use is con-
authored by both Haxel
troversial because these
and Meinig and published last month in the blasts can harm nearby animals.
peer-reviewed science journal PLOS ONE,
At times, the research air gun was loud
chronicles the glider’s travels and explains enough to register “above the sensitivity
how this technology allows scientists to lis- threshold we could measure,” Haxel said,
ten to the sea and explore its murky depths. though the scientists were using a particu-
“This is a new way to make measure- larly sensitive hydrophone.
ments that inform us about what’s going on
Still, on the whole, the scientists found
out there,” Haxel said.
that ocean noise off the coast had remained
Most ocean gliders operate without pro- similar to measurements from the 1990s
pellers or any propulsion system at all.
taken from fi xed moorings.
Instead, they carve through the water
Large vessels did not have as signifi -
because of their wings, which angle cant an impact on overall noise levels as
against the saltwater as the robot adjusts its Haxel had expected. The scientists com-
buoyancy.
pared tracking data from ships and found
“We use the wings to adjust the attitude little correlation between overall noise and
and the fl ight path,” Meinig said.
ship presence.
Mechanical rudders are often equipped
“That was an eye-opener for me. I used
to help keep the machine on course. Bat- to think ships are so loud,” Haxel said. But
teries inside the tubular machine can move along the continental shelf, which features
and adjust its ballast.
an uneven sea fl oor, an energetic, wavy
When gliders surface, they can commu- ocean surface and unique physical prop-
nicate with satellites, share data and get erties in the water column, sound emanat-
instructions from their handlers. Then, they ing from ships seemed to get “trapped” and
dip back down to a programmed depth, have “limited range,” he said.
before beginning to climb through the
These results can’t be extrapolated to
water again.
other locations.
Scientists use gliders to gather ocean
“Your sound velocity profi le is going to
temperatures, information about salinity look a lot different in Puget Sound,” Haxel
and myriad other measures.
said.
Seagliders were invented at the Univer-
Gliders have been used to map the sound
sity of Washington. These robots have been of erupting underwater volcanoes, help
searching the ocean for clues to science’s with National Oceanic and Atmospheric
mysteries for about 15 years, Meinig said. Administration hurricane forecasts and
But the technology continues to develop.
also to listen to deep-diving baleen whales.
Because gliders do not have propellers,
They’ve fl own through the Blob-like
the quiet machines rarely disrupt normally marine heat wave roiling the Pacifi c Ocean,
skittish animals, Haxel said.
in the Bering Sea near Alaska and beneath
“They’re kind of sneaky,” he said.
ice at both polar continents, Meinig said.
Hydrophones, which are essentially
“There’s probably more simple robots
underwater microphones, have allowed sci- in the ocean than anywhere else,” Meinig
entists to gather acoustic data from gliders said. And with gliders, “We’re doing ever
for many years.
increasing and challenging things.”
But studies of ambient ocean noise have
Each fl ight, these robots reach a bit fur-
typically relied on fi xed moorings, which ther into the unknown.
By EVAN BUSH
Seattle Times
Oregon State University
Oregon State University acoustic engineer Haru Matsumoto dives behind a glider being tested
in Kona, Hawaii. After testing, scientists sent the glider on an 18-day trip along the Washington
state and Oregon coast to listen to ocean noise and record what it heard.
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