At the European Marine Energy Centre’s Fall of Warness test site in Orkney, Scotland, researchers completed 45 drifting acoustic surveys around Orbital Marine Power’s O2 tidal turbine.
Marine animals rely on underwater sound to navigate, communicate, and find food, often hearing operational submerged machinery long before seeing it.
Field teams deployed drifting hydrophones around the turbine with vessel engines and sonar powered down to avoid artificial noise. While drifting with the tide reduces sensor-flow noise rather than eliminating background sound entirely, researchers perform baseline control drifts to measure ambient ocean noise during analysis.
How floating hydrophone arrays are applied to survey methodology
Stationary seabed hydrophones in high-velocity tidal channels pick up heavy self-noise as turbulent water rushes directly over the sensors. To solve this, the survey team used a drifting methodology based on the international standard IEC TS 62600-40:2019.
The equipment setup used SoundTrap audio recorders encased in drogues suspended roughly 16 feet below the surface.
Each hydrophone attached to a surface buoy linked to a floating marker equipped with a high-visibility flag, light, and GPS tracker for precise positioning.
The University of Washington’s DAISY drifting system design guided this equipment configuration.
During active survey runs, crew members shut off the research vessel’s engines and depth sonars entirely. With vessel propulsion turned off, hydrophones drifted naturally with the tidal current.
Field teams used drifting hydrophones with vessel engines and sonar shut off to eliminate boat interference and reduce flow-induced turbulence. Control drifts were also conducted to account for ambient ocean noise.
Baseline control runs and Fall of Warness operations
Fieldwork started with control measurements recorded at Westray South, located northeast of the Fall of Warness site in Orkney.
Executed during spring tides, these control runs recorded ambient background noise in a similar tidal channel without operating turbines.
While drifting in the flood tide, hydrophones reached distances of more the 3,280 feet. This set a baseline for the ambient sounds of the ocean. When the control testing was over, survey crews spent two days drawing acoustic measurements around the Orbital O2 turbine while it was operating.
Researchers ran drifts along the device’s port side on day one and focused on downstream acoustic spread on day two.
Field teams completed 45 total drifts, with most individual runs lasting about three minutes. On the final four drifts, technicians deployed two drifting hydrophones at once.
Using paired sensors allowed researchers to test acoustic source localization techniques across the turbulent test site footprint.
Acoustic data processing and environmental findings
Why did scientists drift past the turbine 45 times with underwater microphones?
Marine animals rely on acoustic cues to navigate, forage, and communicate in turbulent coastal channels, making operational turbine noise a central factor in environmental assessments.
Fixed monitors on the seabed struggle in high-flow areas because rushing water creates heavy friction noise across the microphone sensors. Drifting hydrophones move at the same speed as the tidal current, removing flow noise and isolating the turbine’s true acoustic output.
After field collection, researchers digitized observation notes, matched GPS positioning logs, and cut raw audio into clear, location-indexed files.
Acoustic monitoring with drifting hydrophones provides an accurate sound profile of operational tidal devices without flow interference.
These empirical datasets enable regulatory agencies and project developers to evaluate sound impacts on surrounding marine wildlife populations.
Factual data for evaluation
In July and August 2025, the European Marine Energy Centre (EMEC) completed 45 drifting acoustic surveys around Orbital Marine Power’s O2 tidal turbine. Processing and analysis of the acoustic recordings remain underway to assess the device’s subsea sound emissions.
The acoustic survey was designed to gather baseline underwater sound data around the O2 turbine, establishing a foundation that can support future evaluations of potential marine life behavioral responses, avoidance ranges, and sound masking.
EMEC team members are currently processing the recordings and synchronizing GPS data for ongoing acoustic analysis.
The European Marine Energy Center Ltd. completed 45 drifting acoustic surveys around the O2 tidal turbine in mid-2025, with data processing and analysis currently ongoing to measure the device’s underwater sound profile.
This empirical framework strengthens environmental risk reviews, supports informed decision-making, and builds the regulatory confidence needed for commercial energy deployment.
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