Promising Theoretical Results for Ocean Remote Sensing Without Emitting Sound
July 31, 2006
Sustained measurements of oceanic currents
and atmospheric winds are important for weather forecasting, controlling transport of pollutants, and
monitoring climate change. Use of acoustic means of monitoring ocean and atmospheric dynamics has
been hampered by high costs of tomographic networks and concerns about possible biological effects of
powerful sound sources. In a paper entitled, "Recovering the acoustic Green's function from ambient
noise cross-correlation in an inhomogeneous moving medium," to be published in the August 4, 2006
issue of Physical Review Letters, Oleg Godin of the NOAA Earth System Research Laboratory, presents
theoretical results that infer the possibility of remote sensing of inhomogeneous flows without emitting
sound.
Background:
In the coupled ocean-atmosphere system, most of the heat is stored in the ocean. Ocean is less volatile than
atmosphere. Long time series of heat content and heat fluxes in the ocean would be invaluable for detecting
and quantifying climate change. Ocean acoustic tomography and thermometry have been broadly discussed
as methods to obtain such time series. However, these methods involve high intensity acoustic sources and
have not been widely implemented because of concerns regarding the impact of the sources on marine mammals.
Significance:
Godin's passive acoustic method utilizes naturally occurring ocean noise as a signal, which could drastically
reduce costs, increase spatial resolution, and eliminate probing signals that can be bothersome to marine
mammals (or to people in the case of atmospheric sounding). This technique represents a valuable "first step,"
especially if it can be applied on scales of tens and hundreds of kilometers necessary to monitor heat and mass
transport through "choke points" in the ocean, such as straits. This research supports NOAA's mission goal of
understanding climate variability and change to enhance society's ability to plan and respond.
Contact: Oleg Godin | More Information: Abstract of Paper |