Observing the Oceans Acoustically
- 1Department of Ocean and Resources Engineering, University of Hawaii at Manoa, United States
- 2School of Marine Science and Ocean Engineering, University of New Hampshire, United States
- 3Takuvik Joint International Laboratory, Laval University, Canada
- 4Nansen Environmental and Remote Sensing Center, Norway
- 5Scripps Institution of Oceanography, University of California, San Diego, United States
- 6Other, Austria
Acoustics play a central role in mankind’s interactions with the ocean and the life within. Passive listening to ocean “soundscapes” informs us about the physical and bio-acoustic environment from earthquakes to communication between fish. Active acoustic probing of the environment informs us about ocean topography, currents and temperature, and abundance and type of marine life vital to fisheries and biodiversity related interests. The two together in a multi-purpose network can lead to discovery and improve understanding of ocean ecosystem health and biodiversity, climate variability and change, and marine hazards and maritime safety.
Passive acoustic monitoring (PAM) of sound generated and utilized by marine life as well as other natural (wind, rain, ice, seismics) and anthropogenic (shipping, surveys) sources, has dramatically increased worldwide to enhance understanding of ecological processes. Characterizing ocean soundscapes (the levels and frequency of sound over time and space, and the sources contributing to the sound field), temporal trends in ocean sound at different frequencies, distribution and abundance of marine species that vocalize, and distribution and amount of human activities that generate sound in the sea, all require passive acoustic systems. Acoustic receivers are now routinely acquiring data on a global scale, e.g., Comprehensive Nuclear-Test-Ban Treaty Organization International Monitoring System hydroacoustic arrays, various regional integrated ocean observing systems, and some profiling floats.
Judiciously-placed low-frequency acoustic sources transmitting to globally distributed PAM and other systems provide: 1) high temporal resolution measurements of large-scale ocean temperature/heat content variability, taking advantage of the inherent integrating nature of acoustic travel-time data using tomography; and 2) acoustic positioning (“underwater GPS”) and communication services enabling basin-scale undersea navigation and management of floats, gliders, and AUVs. This will be especially valuable in polar regions with ice cover. Routine deployment of sources during repeat global-scale hydrographic ship surveys would provide high spatial coverage snapshots of ocean temperatures. To fully exploit the PAM systems, precise timing and positioning need to be broadly implemented. Ocean sound is now a mature Global Ocean Observing System (GOOS) “essential ocean variable”, which is one crucial step toward providing a fully integrated global multi-purpose ocean acoustic observing system.
Keywords: Acoustical oceanography, ocean sound, Passive acoustic monitoring, acoustic thermometry, Ocean acoustic tomography, Acoustic positioning, multi-purpose acoustic networks, marine bio-acoustics, soundscape, Essential Ocean Variable
Received: 01 Nov 2018;
Accepted: 05 Jul 2019.
Edited by:Tong Lee, NASA Jet Propulsion Laboratory (JPL), United States
Reviewed by:Dimitris Menemenlis, NASA Jet Propulsion Laboratory (JPL), United States
Carl Wunsch, Massachusetts Institute of Technology, United States
Copyright: © 2019 Howe, Miksis-Olds, Rehm, Sagen, Worcester and Haralabus. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Bruce M. Howe, University of Hawaii at Manoa, Department of Ocean and Resources Engineering, Honolulu, United States, email@example.com