The tests using cofferdams were carried out by Hojbjerg, Denmark-based marine consultants Advanced Offshore Solutions at the end of 2011 at the request of the German Federal Maritime and Hydrographic Agency (BSH). The aim is to test the effectiveness of the system, which can work at water depths of up to 45 metres, before deployment later this year.
"The concept is based on the physical principle that if you decouple the pile from the water, the noise will be transferred into the air, which of course is compressible" said Kurt Thomsen, CEO of Advanced Offshore.
"When the cofferdam is open to the atmosphere, the air will disappear upwards and therefore transport most of the noise away from the water column.
"Our patent is therefore an industrialised version of the cofferdam which works in a fast and flexible way in different water depths securing noise mitigation and therefore providing passive noise reduction for pile driving offshore."
Last week at the Coastal Futures event in London, professor Han Lindeboom of Dutch research institute IMARES warned against building offshore wind farms in marine protection areas because of the effect of noise, specifically hammering monopiles, on sea life.
He said there was clear evidence that mammals such as harbour porpoises had moved away from wind farm sites during construction. "Floating turbines are definitely better for wildlife in terms of construction disruption," he said.
The Advanced Offshore cofferdam system has now been declared ready for use by the BSH and will be implemented for the first time in two offshore projects in the German North Sea in July this year.