Abstract
Underwater noise was measured at 25 German offshore wind farms (OWFs) under standardized conditions. The measurements included different turbine types up to 8 megawatt rated power and different foundation types. Water depths ranged from 18 m to 40 m. The two main measurement positions were 100 m from a pre-selected offshore wind turbine (OWT) and in the center of the OWF. Underwater sound was recorded for up to 6 weeks to cover different wind and turbine conditions. The aim was to identify the most relevant influencing parameters of noise radiated by operating OWTs.
The cross-project analysis, based on broadband levels as well as third octave spectra and data, was divided into three wind classes that covered the range from OWT idleness to rated power. Noise from OWTs with gear boxes was slightly higher compared to those with direct drives. No significant differences were found for different foundation types. A trend analysis shows that an increase of radiated noise with increasing turbine size (characterized by its rated power) statistically does not exist. Noise from wind farm-associated vessel traffic was estimated for an exemplary OWF with 87 turbines and was found to be approx. 11 dB lower than the noise radiated by the OWTs.