Ocean Acoustic Tomography

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Ocean Acoustic Tomography
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What is it?

• The problem of ocean acoustic tomography is to
  infer from precise measurements of travel time,
  or of other properties of acoustic propagation,
  the state of the ocean traversed by the sound
  field.
• -Walter Munk, Ocean Acoustic Tomography

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A Brief HistorySubmarine Warfare
Bathythermograph

• During WWII, Athelstan Spilhaus improves SONAR
  accuracy by inventing the bathythermograph a
  device which measures ocean temperature
  stratification
• In 1979, Walter Munk and Spilhaus independently
  propose the inverse problem that of determining
  the temperature distribution by acoustic
  tomographic methods

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ApplicationOcean Circulation Modeling
99 of the oceans kinetic energy is associated
with features that are only 100 km in diameter
(mesoscale)
mesoscale
100 km
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Experimental Setup
C Sound Speed u Velocity Field
Research Vessel A
tmesoscale 100 days
Research Vessel B
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Method
SOFARChannel
ray
Depth (km)
source
Temperature profiles can be inferred by comparing
the arrival times of each distinct mode
300 km
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The SOFAR Channel

• Discovered by Maurice Ewing and Leonid
  Brekhovskikh 60 years ago
• Discovered by humpback whales 45 million years ago

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Data
An ocean acoustic tomographic image of velocity
fields about the Hawaiian Ridge taken between
FLIP and various other vessels/instruments
Resolution of 4 mK over 200 km at 1 km depth
A 3-point tomographic array situated east of Bear
Island in the Barents Sea recording sound speed
at 10 minute intervals for approximately 10 hours
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InstrumentsFloating Instrument Platform (FLIP)
FLIP was designed and built in 1962 for the
Office of Naval Research and is currently
operated by the Marine Physical Laboratory of the
Scripps Institution of Oceanography in La Jolla,
California
Vertical operation makes FLIP more stable than
traditional research vessels
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References

• W. Munk, P. Worcester, C. Wunsch, Ocean Acoustic
  Tomography. Cambridge University Press, 1995
• maps.google.com
• www.wikipedia.org
• www.oal.whoi.edu