Underwater Noise Measurements in the North Sea in and near the Princess Amalia Wind Farm in Operation

The Princess Amalia Offshore Wind Farm is one of the first two operational offshore wind farms near the Dutch shore. One of the conditions imposed by the legislator was to monitor the underwater noise during operation of the wind farm. Ambient sound pressure levels were determined at a location at 100 m from a turbine and a location outside the farm (at 3.8 km), during 12 days. In order to check if the turbine contributes to the ambient noise levels, the sound pressure levels at both locations are compared for three wind speed ranges. For all wind speeds, the time-average broadband sound pressure levels on both locations showed no significant differences. Some tones (<1 kHz) from the gearbox transmission of the turbine could be detected in the narrowband spectrum of the sound pressure measured at the location close to the turbine, but these do not dominate the broadband SPL. These tones were not detected at the location outside the wind farm. It is unlikely that these tones are perceived by harbour porpoises at 100 m distance from a turbine. In these measurements the operational wind farm does not significantly contribute to the ambient noise due to shipping and surface waves.