Manuscript Title: Installing Offshore Wind Turbine Foundations Quieter: A Performance Overview of the First Full-Scale Demonstration of the AdBm Underwater Noise Abatement System

Offshore wind is a quickly-emerging market resulting from the worldwide transition towards renewable energies. Whilst this transition has countless environmental benefits, the negative aspects pertaining to underwater noise generated during wind park construction are coming under increased public scrutiny. A number of countries have responded to this environmental and social concern by establishing underwater noise regulations. Construction using current piling techniques often requires the use of underwater noise mitigation systems to meet these legislative requirements. These systems can be applied at the piling source, near pile or far from pile. Under the Underwater Noise Abatement System (UNAS) program, partially sponsored by the Dutch government’s ‘Rijksdienst voor Ondernemend Nederland’ (RVO), a new noise mitigation system has been tested. The UNAS consortium consists of three partners: Van Oord Offshore Wind Projects, AdBm Technologies, and TNO (Netherlands Organization for Applied Scientific Research). The noise mitigation system, here after referred to as NMS, consists of a slatted system containing Helmholtz resonators which is deployed around a monopile in a similar method to venetian blinds. Scaled tests of the NMS at Butendiek and Luchterduinen Offshore Wind Parks showed potential for full-scale deployment. The full-scale test of the NMS was executed in the fall of 2018. A configuration where the vertical spacing of the slats was 0.67 m yielded a 7 to 8 dB SEL re 1 μPa2s reduction compared to the unmitigated scenario, while combining the NMS with a big bubble curtain (BBC) resulted in a 14 to 15 dB SEL reduction compared to the unmitigated situation. This reduction range, as well as a smooth offshore operational performance, puts the NMS in line with other near pile mitigation systems. Deployment of the NMS appears a feasible option to ensure underwater noise compliance in various nation’s legislation.