Temporal and spatial accumulation of underwater noise from wind turbine generators and supply vessels within an offshore wind farm during operation

Offshore wind farms (OWFs) are vital to sustainable energy but generate noise from both noise-intensive construction and decade-long operation. This study investigates continuous operational noise from wind-turbine-generators (WTGs) and OWF-related service vessels. Based on long-term underwater noise measurements and automatic identification system data, 24-h average noise maps were calculated to represent the temporal and spatial cumulative effects of multiple WTGs in combination with service-related vessel traffic, using a time-weighted, range- and frequency dependent propagation model for the selected OWF area. These maps are essential for applications such as project specific environmental-impact-assessments (EIAs) and strategic spatial planning. In situ measurements showed that WTG-generated broadband-noise was 10-20 dB lower than service vessel noise at same distance. The broadband source levels used in the simulation were approximately 151 dB re 1 μPa2 for a single WTG operating at rated power and 171 dB re 1 μPa2 for service vessel. Model results indicate that combined operational noise from WTGs can produce unweighted broadband sound pressure levels up to 112 dB re 1 μPa2 at distances of around 2 km. Service vessels may further extend the acoustic impact range depending on its duration of operation and location, which highlights that vessel noise shall be taken into account in EIAs.