From communication to foraging, a broad range of marine animal activities depend on sound. The introduction of a new anthropogenic noise source could, under some circumstances, have consequences for individuals or populations. Therefore, understanding the radiated noise produced by a novel source is critical to establishing its potential for environmental impact. The international consensus standard (IEC TS 62600-40:2019) establishes the methodology for radiated noise measurements around marine energy converters. Following these guidelines, we used drifting passive acoustic platforms, the Drifting Acoustic Instrumentation SYstems (DAISYs), to collect data around a cross-flow tidal turbine installed at the University of New Hampshire’s Tidal Deployment Platform in Portsmouth, NH. Our goals were (1) to measure radiated noise from the operating tidal turbine, (2) to evaluate the potential for source localization with multiple DAISYs to objectively identify sound sources, and (3) to develop feedback to inform future revisions to the consensus standard.
Over two days in July 2021, we performed 39 drifts in the vicinity of a New Energy turbine deployed adjacent to the Memorial Bridge. The platform deployment method meant that only the rotor was below water, while the generator and power electronics were airside. During these drifts, the water currents varied from 0.2-2.2 m/s, and the turbine power output varied from 0-4.67 kW. Spectrograms and periodograms of the drifts were generated for frequencies up to 200 kHz and compared across drifter locations and turbine power states. Ambient noise levels at the site were high due to relatively high vessel traffic density and vehicular traffic noise propagating from the bridge piers. Consequently, we could identify no distinctive turbine noise signature in any measurements (i.e., ambient noise levels appear to have generally exceeded radiated noise from the turbine). To assess source localization by groups of DAISYs, hammer strikes to the turbine shaft were used to create a “cooperative”, impulsive noise source at a known location. These signals were identifiable in the time series data and could be localized, although low signal-to-noise ratios resulted in poor accuracy for the time delay of arrival localization techniques. In contrast, when DAISYs and cooperative strikes were used to test localization at a similar site with significantly less ambient noise in April 2022, the sounds could be localized with accuracy. This shows that the localization can yield valuable results if the signal-to-noise ratio is high enough. Overall, this work confirms observations of the turbine at the Tidal Deployment Platform by a team of researchers from Pacific Northwest National Laboratory using similar drifting measurements that concluded the radiated noise from this turbine has a negligible contribution to the environment compared to boats and vehicles. To identify and localize acoustic signals from cross-flow tidal turbines, future work will require environmental conditions with lower ambient noise and/or turbines with more intense radiated noise.