Wind energy is increasingly being used as an alternative energy source. Winds tend to be stronger and more uniform at sea than on land. In addition, there are large, potentially productive areas available offshore. Underwater sound is generated during the construction, operation, and decommissioning of offshore wind turbines. Construction of wind turbines involves a variety of activities including pile-driving. Pile-driving produces high sound pressure levels in both the surrounding air and underwater environment. When a pile is struck, it is like ringing a bell or like a hammer blow - the pressure (sound) wave travels to the bottom of the pile and bounces back up and down again. The sound radiates loudly in the water, sediment, and air. How much sounds associated with pile-driving contribute to the existing ambient noise in a region is an important area of research.
The construction of the first U.S. offshore wind farm, off the coast of Block Island, RI, is providing an opportunity to learn about the potential effects of pile driving on the environment and how best to assess these effects. The Bureau of Ocean Energy Management (BOEM) has funded a study to investigate pile-driving noise in North Atlantic waters. Dr. James Miller, a professor of ocean engineering at the University of Rhode Island, is on a team of scientists and students conducting acoustic monitoring of the pile-driving phase of the wind farm’s construction. Pile-driving has been investigated extensively in the Gulf of Mexico, where offshore oil and gas platforms are abundant. However, the marine life, water conditions, and sediments are very different there, so its effects may be very different in the North Atlantic.
Seafloor characteristics influence the amount of pile-driving activity needed to construct a wind farm at a specific location. In addition to affecting the duration of pile-driving, Dr. Miller and the team are particularly interested in the sediments off Block Island because the sediment affects the propagation of sound in the water. Sediments that are sandy, such as those found in some regions off the coast of Block Island, would allow for longer-range propagation of sound energy.
Understanding the propagation of acoustic energy will provide insights into the potential effects of the construction of wind farms on marine life. While construction operations are very loud and produce sounds with large pressures, as the sounds propagate away, they change to lower intensity, longer duration signals. Dr. Miller and the team are investigating where sounds associated with pile-driving transition from high intensity, short duration signals to low intensity, long duration signals.
Hydrophone have been placed in the water at various distances from the construction site to collect data about the noise levels generated by the pile driver. In addition, on some days when the pile-driving is occurring, the researchers are towing a 200-foot array of hydrophones on a route away from the construction site. Measurements of airborne noise and the visual impacts of the construction are also being taken.
Science of Sound: Ocean Noise Variability and Noise Budgets
Science of Sound: What happens when sound pressures are large?
Animals and Sound: Potential Effects, Masking
Audio Gallery: Wind Turbines
Audio Gallery: Pile-driving
Technology Gallery: Hydrophone Array
Scientist Gallery: Dr. Jim Miller
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