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Low-frequency ocean surface noise sources

1985; Acoustical Society of America; Volume: 78; Issue: S1 Linguagem: Inglês

10.1121/1.2022686

1520-9024

William M. Carey, Marshall Bradley,

Oceanographic and Atmospheric Processes

The interaction of the wind with the ocean surface has long been recognized as the major source of ocean ambient noise. High-frequency noise data 1200 to 2 kHz) has consistently been found to have strong wind-dependent characteristics associated with spray, splashes, bubbles, and rain. Recently, wave-wave interaction has been shown to be a source of infrasonic (0.2 to 2 Hz) noise and ocean bottom microseisms. Generally, the low-frequency noise (2 to 20 Hz) is associated with noise from distant ships. However, narrow-hand (as opposed to 1/3-octave) measurements show in addition to the noise from ships a wind-dependent characteristic. Furthermore, mid-ocean basin vertical directionality measurements show noise intensity near the horizontal with a broad frequency characteristic in diverse geographic locations. These results suggest a wind-generated noise due to a mechanism such as wave-wave interaction, wind turbulence, or the interaction of surface waves with turbulence is coupled into the mid-basin sound channel by either a shallowing sound channel such as found at high latitudes or a down-slope conversion process due to the basin boundaries and sea mounts. Theoretical expressions are derived from first principles following the approaches of Yen and Pertone [Naval Underwater Systems Center TR5833 (1979)] and Huon Li [Naval Ocean R&D Activity, TN89 (1981)] yielding the frequency-dependent radiation characteristics for wave-wave interaction, wind turbulence, and wave-turbulence interaction. These results show that wave-turbulence interaction is a possible source of wind-driven noise in the 10- to 200-Hz regions. Other possible mechanisms such as nonlinear capillary wave interactions are discussed and compared to this wave-turbulence mechanism.