Abstract
The underwater sound emitted during the operation of the Atlantis AR1500 turbine, a 1.5 MW three bladed horizontal axis tidal-stream turbine, was measured in the Pentland Firth, Scotland. Most sound was concentrated in the lower frequencies, ranging from 50 to 1000 Hz. Within 20 m of the turbine, third-octave band sound pressure levels were elevated by up to 40 dB relative to ambient conditions. In comparison, ambient noise at these frequencies fluctuated by about 5-10 dB between different tidal states. At the maximum recording distance of 2300 m from the turbine, median sound pressure levels when the turbine was operational were still over 5 dB higher than ambient noise levels alone. A higher frequency, tonal signal was observed at 20 000 Hz. This signal component appears at a constant level whenever the turbine is operational and did not change with turbine rotation rate. It is most likely produced by the turbine's generator. This study highlights the importance of empirical measurements of turbine underwater sound. It illustrates the utility and challenges of using drifting hydrophone systems to spatially map operational turbine signal levels with reduced flow noise artefacts when recording in high flow environments.
Highlights
Climate change and loss of biodiversity are the most pressing challenges for modern, global societies (Steffen et al, 2018)
The turbine signal was tonal with an oscillating fundamental frequency at about 100 Hz, and several harmonics clearly visible up to 2000 Hz
In close range to the turbine (
Summary
Climate change and loss of biodiversity are the most pressing challenges for modern, global societies (Steffen et al, 2018). The global mean surface temperature is projected to arrive at 1.5 C above pre-industrial levels during 2030–2052, and the recent IPCC Special Report clearly stated that limiting warming to 1.5 C is required to maintain substantial amounts of global ecosystems and significantly reduce the risks of climate change to human health and global economies (Hoegh-Guldberg et al, 2019). Due to this urgent need to stabilise global climate change, there is an increasing demand for clean energy, and, correspondingly, the marine renewable energy sector has grown rapidly in recent years (Gattuso et al, 2018). In the case of tidal-stream energy, environmental concerns have primarily focused on the potential risk of injury to animals related to collision with moving parts of underwater turbines (Band et al, 2016; Waggitt and Scott, 2014; a)This paper is part of a special issue on The Effects of Noise on Aquatic Life
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