Acoustic Monitoring and Validation of Noise Mitigation for Offshore Pile Driving

Abstract

Offshore wind energy is a key resource in the renewable energy sector, with a growing number of monopile foundations being installed for wind turbines. The installation of these piles generates high levels of underwater noise, which can pose risks to marine species. High-level experiment data sets are essential to quantify the pressure, particle motion in both seawater and seabed and vibration of the monopile, allowing for the monitoring of sound levels and the assessment of environmental impact. This is done by comparing measured noise to regulatory thresholds and auditory injury criteria for marine mammals, fish, sea turtles, and benthic communities. Noise mitigation systems, such as air-bubble curtains, play a significant role in reducing underwater noise. Ensuring their effectiveness requires monitoring key parameters, including the pressure distribution along bubble curtain hoses, which governs air flow through the nozzles and ultimately determines acoustic performance. In this study, medium-scale tests were conducted to measure pressure distribution along hoses at varying air flow rates and compare the results with numerical predictions. Additionally, acoustic measurements were performed during an offshore installation campaign in German waters, with hydrophones deployed at multiple locations and distances from the pile. The collected data serves as a benchmark for validating noise prediction models for offshore pile driving across various scenarios, including those with and without noise mitigation measures. These measurements enable the validation of modelling approaches and the evaluation of the effectiveness of applied noise mitigation techniques. Future work will focus on laboratory-scale tests to monitor particle motion in the water column and seabed vibrations. This will help assess the environmental impact on species that are particularly sensitive to these physical changes.