Model for underwater noise due to bubble clouds and comparison with observations from Monterey accelerated research system observatory

Abstract

Empirical models for underwater noise spectrum from bubbles suggest a general increase by 5 dB for every doubling of wind speed. However, at wind speeds greater than 10 m/s and frequencies higher than 10 kHz, observations report a decrease in noise with increase in wind. This is due to the formation of bubble clouds, which radiate sound, but also attenuate the intensities because of the air contained within them. The bubble clouds occur in certain shapes called α, β, and γ plumes, which evolve during the various stages of wave-breaking. There are yet no quantitative underwater noise models that combine the nature of these clouds, with their acoustics. This paper builds the model in two steps. First, inputs such as wind speed and wave height are used to approximate the clouds as spheres, with respective number of bubbles of each radius and mean spacing between the clouds. Second, this approximate model is then used to predict the radiated sound. To test the model, predictions are setup for comparison with measured noise during high winds around Monterey, California. To input relevant environment parameters to the model, the work uses measurements of wind-velocities, and wave-heights, measured on-site. For acoustic recordings, the work uses hydrophone from the Monterey Accelerated Research System (MARS) cabled observatory.