Breaking wind waves as a source of ambient noise

Area of Science:

• Ocean acoustics
• Fluid dynamics
• Wave mechanics

Background:

• Breaking wind waves generate significant underwater ambient noise.
• Air bubbles entrained by breaking waves play a crucial role in sound generation and propagation.
• Existing models may not fully capture the spectral characteristics of bubble-induced noise.

Purpose of the Study:

• To develop a theoretical model for predicting ambient noise levels caused by collective air bubble oscillations under breaking wind waves.
• To quantify the acoustic power radiated by a bubble cloud using an energy flux budget from breaking waves.
• To investigate the frequency shift in noise spectra attributed to collective bubble oscillations.

Main Methods:

• Formulation of a theoretical model based on energy flux budget.
• Quantification of acoustic power radiated by bubble clouds.
• Assumption of spectral shift to lower frequencies due to collective bubble oscillations.
• Validation of model estimates against wind speed and breaking wave height.

Main Results:

• The model provides good estimates for the magnitude of ambient noise spectra.
• The model accurately predicts the slope of the noise spectra.
• The model effectively determines the frequency range of the noise spectra.
• Model performance is linked to wind speed and breaking wave characteristics.

Conclusions:

• The developed theoretical model offers a robust method for predicting ambient noise levels in the ocean.
• Collective oscillations of air bubbles significantly influence underwater sound spectra.
• Wind speed and breaking wave parameters are key determinants of bubble-induced noise characteristics.