Wind energy is increasingly being used as an alternative energy source. As wind turbines have moved from land into ocean waters, sound is being used to find the best location for offshore wind farms. The potential effects on the environment and marine life of the sound generated by the construction and operation of wind farms also need to be considered when siting wind turbines.
When selecting a location for an offshore wind farm, the water depth and seafloor characteristics need to be evaluated. The type of wind turbine determines the water depth that is acceptable for its placement. Stationary wind turbines are usually located in water depths of less than 20 meters, whereas floating wind turbines can be placed in depths over 200 meters. Water depth is most often measured with underwater acoustics, using equipment such as an echosounder.
Seafloor characteristics determine how difficult it would be to construct a wind farm at that location. In regions where there is little sediment over the bedrock extensive drilling is required to install wind turbines, whereas pile driving for turbine installations is easier in areas where the sediment layer is deeper. Underwater acoustics is used to map and characterize ocean sediments, using equipment such as multibeam echosounders and side scan sonars.
Construction and operation of offshore wind farms create unwanted sound or noise. How much this noise will contribute to the existing ambient noise in a region is an important area of research. Dr. Jim Miller at the University of Rhode Island has measured the existing sound field off Block Island, Rhode Island, the proposed location of an offshore wind farm. Using measurements of the noise from one turbine in an offshore wind farm off Sweden, he estimated the amount of noise the proposed wind farm would add to the ambient noise off Block Island (for more information, please see the Advanced Topic on Noise Budgets). To learn more about this research, please visit the podcast at: http://coseenow.net/podcast/tag/alternative-energy/.
There is also the concern of the potential effects of the construction and operation of wind farms on marine life. While construction operations are very loud and may temporarily affect marine animals, long-term increases in ambient noise due to the operation of a wind farms could cause masking that might affect feeding and reproduction. Measurements of the noise from the pile-driving construction of a wind farm off Scotland estimated that bottlenose dolphins would experience auditory injury within 100 m and behavioral reactions at distances of up to 50 km from the wind turbines . Harbor porpoises have been shown to decrease their echolocation activity during construction . Harbor porpoises were also masked by operational noise when sound levels were at 128 dB at 0.7, 1.0, and 2.0 kHz, but not at sound levels of 115 dB . It is believed that harbor porpoises would hear operational noise at distances of 20 to 70 m, whereas harbor seals would hear operational noise at less than 100 m up to several kilometers . More studies on the effects of wind farms are needed, particularly as new turbines are designed.
- Behavioral Changes
- Dr. Jim Miller
- How is sound used to measure water depth?
- Multibeam Echosounder
- Ocean Noise Variability and Noise Budgets
- Side Scan Sonar
- Bailey, H, Senior, B, Simmons, D, Rusin, J, Picken, G, Thompson, PM. 2010, "Assessing underwater noise levels during pile-driving at an offshore windfarm and its potential effects on marine mammals." Marine Pollution Bulletin 60: 888-897.
- Cartensen, J, Henriksen, OD, Teilmann J. 2006, "Impacts of offshore wind farm construction on harbour porpoises: Acoustic monitoring of echolocation activity using porpoise detectors (T-PODs)" Marine Ecology Progress Series 321: 295-308.
- Lucke, K, Lepper, PA, Hoeve, B, Everaarts, E, Elk, N, Siebert U. 2007, "Perception of low-frequency acoustic signals by a harbour porpoise (Phocoena phocoena) in the presence of simulated offshore wind turbine noise." Aquatic Mammals 33: 55-68.
- Tougaard, J, Henriksen, OD, Miller, LA. 2009, "Underwater noise from three types of offshore wind turbines: Estimation of impact zones for harbor porpoises and harbor seals." Journal of the Acoustical Society of America 125: 3766-3773.
- "Faculty page for Dr. James A. Schneider." (Link)
- Miller, JH, Potty, G, Vigness-Raposa, KJ, Casagrande, D, Miller, LA, Nystuen, JA, Scheifele, PM, and Clark, JG., "In Press. Environmental assessment of offshore wind power generation: Effect on a noise budget." Springer-Verlag. Proceedings of the 2nd International Conference on the Effects of Noise on Aquatic Life. (Link)