Aleutian Islands Deep Water Corals Cruise, July 30, 2004
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Guest journal by Gary Greene Marine Geologist, Moss Landing Marine
Laboratories and the Monterey Bay Aquarium Research Institute
(Read how sound is used to explore the seafloor:
Part I and II)
Part I: Blind As A Bat:
Sounds of Science at Sea
In the darkened Deep Submergence "control van", scientist Gary Greene
uses his computer to select images of the seafloor for later study.
Behind him is one of the maps used to guide the expedition. Photo by Sonya Senkowsky.
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Sound controls our lives at sea, especially if you are a geophysicist. It
is what we use to tell us what lies in the water, how the sea floor is
configured and what lies beneath the floor of the ocean. Onboard ship, it
tells us when things go wrong or when things are going well. Sounds are all
around us, and in this noisy environment we sort out the routine of seaboard
life and scientific data collection.
Bells and whistles let us know if a fire has started or if the
vessel is about to sink (or, more likely, that the crew is conducting a
drill) so that we can reach for our survival suits and rush to the life
rafts. The sounds of the constant hum of blowers, motors, thrusters and the
thrashing of the large propellers tell us that things are normal, and
whether the ship is underway surveying or keeping station for sampling and
seafloor observations.
My day at sea on the Revelle generally starts with a gentle knock on
the door of my cabin, located deep in the ship up against the starboard
(right) side. It is 3:30 in the morning and time to relieve the watch in the
Deep Submergence control van several decks above my cabin. In the dark of
the cabin, I struggle to dress and collect all the things I will need to
stand my four-hour-long watch. In this dark environment, I collect the
sounds around me and assess the state of the vessel and its operation. Do
the motors sound right? Is water rushing past the hull or is it gently
lapping up against it? This assessment prepares me for what to expect when I
reach the control van.
Sometimes the knock does not come. I awake anyway. In the dark, I
can hear the sweep of sound and hard click against the hull from the multibeam
echosounder, which sounds like a birdcall. This instrument is used
to image the seafloor, using sound to give precise depth information based
on the reflected and random scatter of sound that returns to the receiver
after being bounced off the sediment or rock below. The duration between the
sweep of sound and the click, along with the intensity of the click, tells
me if we are in deep or shallow water. If the click taps the hull like a
hammer would, and the duration between the sweep of initial noise and the
click is short, I know that we are in shallow water. If the click is barely
detectable and arrives long after the initial sweep of sound, I know we are
in deep water.
So, this day that the knock does not come, I know that something has
changed, either because of an instrument malfunction or from a change in
plans. The echosounder noise tells me if we are in shallow water. The
lapping or swishing of water along the hull outside of my cabin tells me if
the vessel is swiftly moving through the water. And, the normal or
interrupted background ship noise tells me if everything onboard the ship is
operating normally. The ship's horn blasting away every 2 minutes to alert
other vessels of our presence tells me that it is foggy on the calm waters.
Armed with this sound assessment, I retreat from my dark cabin to the
lighted world of the ship's interior. I grab a cup of coffee in the mess and
slowly make my way to the control van, confirming my initial assessment of
conditions based on sound.
So, like bats, we marine geologists rely upon sound to navigate and image
the surroundings around us, the deep sea. Try it. The next time you get up
in the dark, don't turn on the lights. Listen. Listen to sounds in your
room. Listen to the sounds outside. Try to determine the activity in your
house and in your neighborhood (you probably do this subconsciously anyway).
Do you hear dishes rattling to indicate someone is up and in the kitchen? Do
you hear the drip and patter of water, which may indicate rain, or a broken
water pipe?
You have now collected and assessed these sounds, an assessment that helps
you plan your day, answering questions such as: Do you need to fix breakfast
or is it being fixed for you? And what you should wear today?
Sound allows us to plan for our daily life, both scientifically and at home.
So off I go for another day at sea using sound to plan and guide me through
this very exciting scientific adventure aboard the Revelle.
Part II >>>
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