Investigating the influence of a bubble curtain on the underwater sound wave field generated by offshore pile driving

Pile driving for offshore wind turbines typically generates high sound levels in the water column. Bubble curtains are frequently employed to protect marine fauna. This study aims to investigate the effect of a bubble curtain on the generated sound wave field. A recently developed seismo-acoustic model was extended by incorporating an established acoustic model of the bubble curtain. Subsequently, a detailed analysis of the sound wave field at an offshore wind farm construction site was conducted using both simulated and measured data. The results indicate a distance- and depth-dependent insertion loss, with reductions of approximately 2 to 4 dB observed at greater distances from the pile. For a more detailed analysis, a metric based on the concept of transmission loss was introduced. This demonstrates that the insertion loss caused by a bubble curtain can be formulated as a sum of two components: the loss due to the interaction between the bubbles and the sound wave field, and the altered bottom loss resulting from the scattering of the sound wave as it passes through the bubble curtain. Analysis of the simulation data highlights that sound scattering and the resulting altered bottom loss significantly contribute to the efficiency of the bubble curtain.