The Impact of Offshore Wind Turbines on Underwater Ambient Noise Levels

The underwater sound levels generated by offshore wind turbine farms is a concern because of the possible environmental impact on marine mammals. This paper will consider how sound generated by a wind turbine is transmitted into a shallow water channel. It is shown that the underwater sound levels can be calculated for a typical offshore wind turbine by using the theory of Chapman and Ward (1990) combined with aeroacoustic models of trailing edge noise on the wind turbine blades. A procedure is given for estimating the underwater sound levels from a wind turbine whose airborne noise levels are known. The results indicate that the sound levels are strongly modulated at the blade passing frequency, which leads to infrasound that is more easily detected than a continuous sound source of the same level.