 |
The
1998 North Pacific Acoustic Laboratory
cruise (NPAL '98) aboard Scripp's
R/V Melville involved deployment
of instrument arrays essential
to the Acoustic Thermometry of
Ocean Climate (ATOC) experiment.
 |
| Map
of a feasibility study of acoustic
thermometry in the North Pacific
Ocean. Lines represent acoustic
paths from sound sources on the
U.S. West Coast and in Hawaii
to U.S. Navy and other receivers.
Paths cover distances of up to
3,100 miles (5,000 km) in the
North Pacific, with a 6,200 mile
(10,000 km) path to New Zealand.
ATOC represents the first attempt
to directly provide average measures
of temperature throughout much
of the Pacific Ocean basin. |
Acoustic thermometry is a method
that was devised for tracking long-term
changes in ocean temperature by using
low-frequency sounds transmitted across
ocean basins at a particular depth.
The technique, which works because
the speed of sound is proportional
to water temperature, was invented
by Walter Monk at Scripps Institute
of Oceanography and Carl Wunsch at
Massachusetts Institute of Technology,
with support from the Office of Science.
It turns out that acoustic thermometry
is a sensitive technique not only
for measuring the average temperature
of vast expanses of ocean but also
for tracking long-term changes in
ocean climate associated with global
warming. The idea works by sending
sound signals from underwater speakers
and tracking how long it takes them
to reach receivers moored to the ocean
floor thousands of miles away. Because
sound travels faster in warmer water;
slower in cooler water, recording
increasingly faster travel times of
the sound waves would indicate the
ocean is warming. The concept was
proven about 10 years ago, when the
Office of Science and several other
agencies demonstrated that acoustic
thermometry could generate high-fidelity
global and basin scale ocean thermal
data.
Scientific Impact:
Acoustic thermometry is more sensitive
than local measurements for tracking
long-term trends in ocean temperature
because it can detect changes in deep
ocean areas that exhibit little, if
any, seasonal or interannual variation.
This technique reduces the time required
to detect a trend in climate warming
from several decades to as little
as a decade.
Social Impact: Acoustic
thermometry helps to improve the science
base for societal decisions and policymaking
with regard to human activities that
contribute to global warming. It may
also reveal information about other
oceanographic phenomena, such as El
Nino events, that have profound effects
on climate.
Reference: Munk,
W. and C. Wunsch, "Ocean Acoustic
Tomography: a scheme for large scale
monitoring. Deep Ocean Research
26: 123-161 (1979).
Munch, W. and C. Wunsch, "Observing
the ocean in the 1990's: a scheme
for large-scale monitoring," Phil.
Trans. Roy. Soc., A307, 439-464
(1982).
URL:
http://atocdb.ucsd.edu/
Technical Contact:
Dr. Ari Patrinos, Associate Director
for Biological and Environmental Research,
301-903-3251
Press Contact: Jeff
Sherwood, DOE Office of Public Affairs,
202-586-5806
SC-Funding Office:
Office of Biological and Environmental
Research |
