As part of the ESRa research project, the handling and effectiveness of five different noise mitigation systems for the construction of pile-driven offshore wind farms were evaluated in a round robin test conducted at the Brodten pile in Lübeck Bay (Baltic Sea). The systems were:
1. Tube with inner bubble curtain by the company IHC (IHC NMS)
2. Fire Hose System by the company Menck (Menck FHS)
3. Little Bubble Curtain (LBC) by the company Weyres
4. Noise-mitigation shells with two bubble curtains (modular design) by the company Weyres (Weyres BeKa Jacket)
5. System 5: Hydro Sound Damper by the TU Braunschweig (TUBS) and Dr.Elmer (TUBS/Elmer HSD)
All systems were used under identical environmental boundary conditions with the aim of comparing potential noise mitigation levels by way of a uniform measuring concept. ITAP GmbH has developed a specific measurement and evaluation concept for underwater noise measurements in compliance with StUK3 requirements; it also conducted and evaluated the measurements.
All noise mitigation systems tested yielded significant reduction effects. Within the 750-metre radius around the noise source that is relevant for the limit value and in the 100 – 300 Hertz frequency range where the greatest amount of energy is introduced into the water, the damping is between 0 and 10 decibel (dB) SEL. In the frequency range of up to 5,000 Hertz, which is the most sensitive audible range for marine mammals, the mitigation effect is a maximum of 25 dB.
With the test systems, the broad-band reduction of the sound exposure level(SEL) is 4.2 to 6.1 dB. Corrected by the ground effect at the test location, the test systems achieved reductions in the broad-band SEL of approx 7 – 9 dB.