Abstract
This chapter examines underwater noise measurements recorded within and outside operating offshore wind farms consisting of 6.3 MW and 8.3 MW turbines, respectively. Each wind farm had multiple hydrophones recording simultaneously with the nearest being located 70–100 m from a turbine, while the furthest was positioned 5 km outside the wind farm. Data were collected over 5 weeks to facilitate a statistical examination of how the magnitude of underwater noise changes with turbine activity (power production data) and natural fluctuations (e.g., tides and wind). The results imply that there is no significant relation between the broadband underwater noise levels and turbine activity for any of the examined wind farms in the monitored distances (up to 70 m). Influence from natural fluctuations was on the other hand evident from the measured noise levels. Moreover, a comparison between recorded noise levels and simulated noise levels from an already-established empirical model shows that the model’s extrapolated noise levels greatly exceed that of the recordings. This suggests that there are challenges associated with extrapolating aggregated results from smaller turbines to the realm of new, larger turbines. Thus, a new approach or more data are required to predict underwater noise from future operational wind turbines.