Acoustic Thermometry of Ocean Climate

Acoustic Thermometry of Ocean Climate
Name	Acoustic Thermometry of Ocean Climate
Acronym	ATOC
First publication	1995
Developers	Woods Hole Oceanographic Institution, Scripps Institution of Oceanography
Country	United States
Related	Tomography (imaging), Ocean acoustic tomography

Acoustic Thermometry of Ocean Climate Acoustic Thermometry of Ocean Climate is a technique using long-range sound propagation to estimate basin-scale ocean temperature changes by measuring travel times of acoustic signals. Developed from research at institutions such as Woods Hole Oceanographic Institution and Scripps Institution of Oceanography, the approach links physical oceanography, signal processing, and climate change studies to provide complementary observations to satellite remote sensing and Argo profiling float networks.

Overview and Principles

The technique exploits the relationship between sound speed and temperature in seawater described by empirical formulations developed by researchers at Mackenzie and refined via work at Scripps Institution of Oceanography and Woods Hole Oceanographic Institution. Long-range acoustic transmissions traverse ocean acoustic channels influenced by large-scale features such as the Gulf Stream, Antarctic Circumpolar Current, and El Niño–Southern Oscillation, producing travel-time shifts measurable by receivers like those deployed by the U.S. Navy and research groups affiliated with Office of Naval Research. The method draws on theory from Lord Rayleigh-inspired wave propagation, normal modes, and acoustic tomography frameworks pioneered in collaborations among MIT, Harvard University, and international partners including Woods Hole Oceanographic Institution teams.

Historical Development and Major Experiments

Conceptual roots trace to early ocean acoustics research at Bell Labs and experimental oceanography projects supported by Office of Naval Research during the Cold War era, with field demonstrations in the 1970s and 1980s by groups at Scripps Institution of Oceanography and Woods Hole Oceanographic Institution. The formal ATOC program in the 1990s involved experiments crossing basins between sites near Killingly Point and Kamchatka Peninsula and deployments coordinated with NOAA and the National Science Foundation. Major experiments include basin-spanning transmissions between the Hawaiian Islands and Alaska, regional trials near the North Atlantic and the North Pacific, and collaborative campaigns with institutions such as WHOI and Lamont–Doherty Earth Observatory examining decadal temperature trends.

Methodology and Instrumentation

Transmitters emit coded low-frequency signals designed by engineers at Scripps Institution of Oceanography and Woods Hole Oceanographic Institution to maximize signal-to-noise ratio across paths influenced by features like the Kuroshio Current and Labrador Sea Water. Receivers from projects supported by Office of Naval Research and National Oceanic and Atmospheric Administration employ hydrophones and arrays developed in partnership with Massachusetts Institute of Technology and Naval Research Laboratory. Instrument suites integrate timing referenced to Global Positioning System sources and clocks traceable to standards at National Institute of Standards and Technology. Data acquisition draws on methods from signal processing groups at Stanford University and University of California, San Diego, while deployment logistics often involve research vessels such as those operated by Scripps Institution of Oceanography and Woods Hole Oceanographic Institution and platforms linked to Arctic Research Commission initiatives.

Data Analysis and Interpretation

Travel-time measurements are inverted using techniques developed in geophysics and adapted by teams at Lamont–Doherty Earth Observatory, Scripps Institution of Oceanography, and WHOI to infer path-average temperature changes and sound-speed anomalies. Statistical frameworks utilize methods from Bayesian statistics groups at Columbia University and Princeton University and incorporate ocean circulation models from Geophysical Fluid Dynamics Laboratory. Analysts compare acoustic-derived signals with independent observations from Argo floats, TOPEX/Poseidon, and GRACE gravity-derived mass changes to separate thermal from steric contributions. Signal processing advances from MIT Lincoln Laboratory and algorithmic developments in time-series analysis by researchers at University of Washington enable discrimination of multipath arrivals, ambient noise from source regions such as North Pacific Gyre, and anthropogenic noise traced to shipping lanes near Panama Canal traffic.

Applications and Findings

ATOC and related acoustic tomography efforts have provided evidence for basin-scale warming consistent with results from Argo and satellite altimetry programs, revealing regional patterns linked to El Niño–Southern Oscillation, Pacific Decadal Oscillation, and shifts in the Atlantic Meridional Overturning Circulation. Studies involving collaborators from NOAA, NSF, and DOE have used acoustic observations to quantify heat storage, constraints for climate model tuning in institutions like NOAA Geophysical Fluid Dynamics Laboratory and Met Office, and cross-validate ocean reanalysis products from groups at ECMWF and Jet Propulsion Laboratory. Results have informed assessments by intergovernmental panels including the Intergovernmental Panel on Climate Change.

Limitations, Controversies, and Environmental Impacts

ATOC has faced debates involving stakeholders such as marine biologists from Scripps Institution of Oceanography and environmental organizations including National Audubon Society over potential impacts on marine mammals like blue whale and humpback whale populations. Regulatory scrutiny involved agencies such as National Marine Fisheries Service and legal considerations referenced by National Environmental Policy Act processes. Technical limitations include sensitivity to ocean dynamics near fronts like the Gulf Stream and challenges separating thermosteric signals from circulation changes studied by Woods Hole Oceanographic Institution teams. Ongoing research by interdisciplinary consortia at Scripps Institution of Oceanography, WHOI, and international partners such as Plymouth Marine Laboratory aims to refine protocols to mitigate ecological concerns while improving climate-relevant measurements.

Category:Oceanography