Promising Theoretical Results for Ocean Remote Sensing Without Emitting Sound


July 31, 2006

dolphinsSustained 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