Acoustic and Electromagnetic noise induced by wind mills - implication for underwater surveillance systems. Pilot study

Authors:

  • Fristedt Tim
  • Moren Per
  • Söderberg Per

Publish date: 2001-01-01

Report number: FOI-R--0233--SE

Pages: 17

Written in: English

Abstract

Underwater vehicles in combination with Sweden´s long coastline and its large number of archipelagoes represent today a threat to the country with regard to surveillance. The prospects of detecting and identifying such types of vehicles are based mainly on underwater acoustic and electromagnetic sensor systems. Modern underwater vehicles are getting more and more silent and their electromagnetic signatures lower and lower, which leads to the fact that it will also be easier for them to hide. There is also a risk that the underwater acoustic and electromagnetic noise level could mask signatures from underwater targets. Until today, only a few measurements performed in the water close to off-shore wind power stations are described. The results from these earlier studies have shown that underwater disturbances can occur. The aim of this preliminary study is to find out how strong the hydroacoustic and electromagnetic disturbances generated by a wind power station could be. Also how such disturbances affect the performance of the passive naval surveillance systems used by the Swedish Armed Forces. We performed a test on August 22-23, 2000, at the wind power park at Bockstigen, Gotland, in order to study the hydroacoustic and electromagnetic fields created by a typical sea-based wind power plant. The result show that the windmill at Bockstigen generates significant hydroacoustic noise, as well as electromagnetic radiation in the water. The measurements are restricted to operating conditions with low wind force and also limited to uncontrolled background levels. This pilot study ends up with some recommendations for further work to clarify if the disturbance can effect the performance of naval surveillance systems. The building of off shore wind power in the Baltic Sea will continue during the coming years. Development of new and more efficient technique in combination with the use of numerical wave propagation models for noise prediction in the water may contribute to facilitate the future planning.

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