UC San Diego

Storms and wind events at the surface of the ocean are known to generate noise through turbulence, water droplets, breaking surface waves, and the entrainment of air bubbles. With larger wind events, waves break at the surface introducing air bubbles into the upper ocean layer. These air bubbles oscillate and generate noise in accordance with their resonant frequency, but they also act as attenuators to incoming acoustic signals by absorbing, reflecting, and scattering sound waves. Presented in this paper is a model for the attenuation of acoustic signals in the frequency range of 2-100kHz due to air bubbles from wind speeds in the range of 5-75m/s. Using a model for the number of bubbles introduced into the water column for varying wind speeds, total attenuation was determined as a function of acoustic frequency and wind speed. It was found that total attenuation increases with both increasing frequency and increasing wind speeds, with a 100kHz signal being attenuated by 355dB for a wind speed of 75m/s. For the same wind speed, a 2kHz signal gets attenuated by roughly 44dB. A 2kHz signal at 5m/s winds however experiences no attenuation due to the bubble cloud, but a 100kHz signal experiences 40dB of attenuation at 5m/s winds. For future work regarding this model, sound generation of the bubbles in the ocean surface layer should be added to get the net total ambient noise for each frequency at certain wind speeds.