Abstract:

An acoustic array was deployed in the near-surface layer in Saanich Inlet, BC, to image breaking waves using only the naturally occurring acoustical radiation in the band (160 and 2000 Hz) from the breaking region. The 15-element array was configured as a horizontal cross with an 8-m aperture, bottom-moored, and positioned nominally 3 m beneath the surface. A novel broadband scheme combined information at six independent frequencies above about 400 Hz to yield unambiguous resolved images. A parametric image analysis shows that the images align closely with the wind and can be observed moving downwind with a speed roughly equal to the dominant phase speed of the wind waves. Absolute power levels are found to be consistent with previously published results. The data also provide inferences regarding the sound generation mechanism at ``collective oscillation'' frequencies below about 400 Hz. [Work supported by ONR.]