The Importance of Empirical Particle Motion Measurements for Monitoring Underwater Noise from Wave Energy Converters

Abstract

The energy transition to achieve NetZero objectives by 2050 2050 needs a sharp increase of Marine Renewable Energies (MREs). This growth must ensure environmental sustainability while aligning with biodiversity conservation goals, as outlined in the EU Biodiversity Strategy. However, significant knowledge gaps persist regarding the impacts of MREs on marine ecosystems, leading to uncertainties in assessing cumulative effects on marine organisms. Comprehensive monitoring and data collection are crucial to enable the sustainable development of MREs. Underwater noise is a recognized stressor associated with MRE devices, including Wave Energy Converters (WECs). It is also classified as an environmental quality indicator under Descriptor 11 of the Marine Strategy Framework Directive (EU), mandating its monitoring during anthropogenic activities as a potential pollutant for marine ecosystems. Standards for MRE devices noise assessment are now available (IEC TS 62600-40). Traditionally, underwater noise monitoring has focused on scalar pressure measurements. However, particle motion—a vectorial measure representing the acceleration or velocity of water particles caused by sound waves—is equally significant, especially in shallow water environments where WECs and their mooring systems may influence soundscapes more through vibration than pressure. Many marine organisms perceive sounds predominantly as particle motion rather than pressure due to their physiological characteristics (i.e. fish and invertebrates). This highlights the need to broaden current noise monitoring frameworks, which primarily focus on pressure, to incorporate particle motion measurements. 

This paper emphasizes the importance of particle motion as a critical component of underwater noise monitoring for WEC applications. We present initial findings from empirical measurements of both particle motion and pressure conducted at a pilot site in the Mediterranean Sea using an underwater acoustic vector sensor (M20-105 system, GTI Geospectrum Technologies Inc.). Acoustic data were collected near the ISWEC (Inertial Sea Wave Energy Converter) off the coast of Pantelleria, Italy, offering novel insights into the underwater noise characteristics generated by WECs and the role of particle motion in their assessment.