Ocean Acoustics: A National Naval Responsibility

The Ocean Acoustics (OA) program supports basic research that addresses fundamental understandings of the physics relating to underwater sound. Passive and active acoustics are of interest, along with theoretical and/or experimental approaches and model development. Core areas of interest include the generation, propagation and scattering of narrow and broadband acoustic (and elastic) waves in the temporally- and spatially-varying ocean environment. Also of interest is research that exploits the information content of acoustic signals to elucidate information about the ocean environment—including the air-sea interface and seafloor. Included under the OA program is research on ocean ambient sound in terms of its spatial, temporal and frequency attributes, and including characteristics of source mechanisms contributing to the overall sound field. New directions for the program will include basic research into generalize auditory scene analysis for the undersea environment. Interdisciplinary basic research involving acoustics is encouraged through coordination with the appropriate directed programs (e.g., Physical Oceanography, Arctic and Global Prediction, and Littoral Geosciences and Optics). Research that addresses an applied problem or warfare area should be discussed directly with the appropriate directed programs (Signal Processing, Ocean Engineering and Maritime Systems). The OA program managers will provide guidance and may jointly support interdisciplinary or applied projects where basic research in ocean acoustics is central to the effort.

Planning Letter/Preproposal and Proposal Process

Planning letters (also referred to as preproposals, white papers or letters of intent) are encouraged in advance of formal proposals for greater efficiency. A planning letter should be a short description (not to exceed two typed pages including figures). The planning letter should contain the following information: telephone number and email address of the originator, the goals and technical approach, relevant references, and an estimate of the funding requested. While our calls for planning letters for the upcoming fiscal year have specific deadlines, unsolicited proposals and planning letters are accepted at any time throughout the year.

Special Ocean Acoustics Awards

ONR awards graduate traineeships, postdoctoral fellowships and entry-level faculty awards in ocean acoustics. Requests should use the preproposal format with any additional guidance found in the Special Research Awards overview page.

Research Concentration Areas

The Ocean Acoustics program contains three thrust areas:

• Shallow-Water Acoustics: This thrust addresses the basic research interests described above in areas of the ocean where the acoustic field is highly influenced by interactions with the seabed.
• Deep-Water Acoustics: This thrust addresses issues associated with low-frequency acoustic propagation, scattering and communication over distances from tens to thousands of kilometers in the deep ocean where the sound channel may or may not be bottom limited.
• Arctic Acoustics: The primary goal here is to understand the effects of changing Arctic conditions on acoustic propagation and ambient noise, particularly in under-ice environments. The thinning ice in the Arctic may result in reduced transmission loss compared to that observed during earlier investigations.

In addition to the investments under these thrusts, we continue to maintain more modest investments in research related to acoustic communications, particularly focusing on understanding and exploiting channel capacity.

Research Challenges and Opportunities

• Shallow-water scattering mechanisms related to reverberation and clutter; seabed acoustic measurements supporting geoacoustic inversion; acoustic propagation through internal waves and coastal ocean processes and the development of unified ocean/seabed/acoustic models, including scattering from rough surfaces, biologics and bubbles; and penetration/propagation within the porous seafloor.
• The effects of environmental variability induced by ocean internal waves, internal tides and mesoscale processes—as well as by bathymetric features including seamounts and ridges—on the stability, statistics, spatial distribution and predictability of broadband acoustic signals remain areas of high interest. Also of interest is the coherence and depth dependence of deep-water ambient noise.