Acoustic sensing using the UK offshore renewable energy archipelago

Acoustic sensing using the UK offshore renewable energy archipelago

The UK has an extensive network of offshore renewable energy (ORE) infrastructure for wind and tidal power generation, and this is growing rapidly to meet the ambition of a net zero future by 2050.

By Philippe Blondel and Anna Young, University of Bath, UK

Above: Figure 1. Crown Estate map of all offshore activity (England, Wales & NI), © The Crown Estate. Published via THE CROWN ESTATE OPEN DATA LICENCE (GIS) – VERSION 1.1. Contains data provided by The Crown Estate that is protected by copyright and database rights

The UK has an extensive network of offshore renewable energy (ORE) infrastructure for wind and tidal power generation, and this is growing rapidly to meet the ambition of a net zero future by 2050. Offshore wind power capacity was 11 GW in 2021 (approximately 10% of the UK’s consumption). Tidal power capacity is currently <10 MW but will be expanding tenfold to almost 100 MW in the next five years with four new or expanding sites in Scotland and Wales. Floating offshore wind has also had its first success in the recent Government Contract for Difference (CfD) auction (32 MW to be installed). The latest map from the Crown Estate (Figure 1, updated April 2024) clearly shows these ambitious activities, along with their connections to shore.

Underwater acoustic monitoring and surveillance network
These rapid expansions in ORE generation give significant opportunities and challenges for infrastructure design and use. In this project we have explored the potential of multi-purposing the UK’s ORE infrastructure to support an extensive underwater acoustic monitoring and surveillance network. The UK Acoustics Network (UKAN+: https://acoustics.ac.uk/) funded us for four months, with a research project entitled Feasibility of a Marine Acoustic Sensing Network using the UK Archipelago of Offshore Renewable Energy (ORE) Infrastructure awarded to Anna Young. Potential applications include monitoring of infrastructure integrity, defence and security of UK waters, biodiversity and population monitoring, underwater navigation and communication, and oceanographic and climate science.

The scope of this project federated several domains around the central theme of underwater acoustics. Anna Young, the principal investigator, is based in mechanical engineering and working on marine turbulence (e.g. with her Barnacle sensor) and tidal turbine design; she leads the University of Bath Research Beacon on Zero-Carbon Offshore Power (https://www.bath.ac.uk/campaigns/bath-beacon-zero-carbon-offshore-power/). Team members included Guillermo Jimenez Arranz (PDRA), Philippe Blondel (based in physics and working on acoustic sensing, e.g. with the FLOWBEC sonars for offshore renewables) and Cormac Reale (based in architecture and civil engineering and working on offshore geotechnics). As the UKAN+ funding enabled us to expand into new initiatives, we are now also working with Alan Hunter (mechanical engineering, sonar expert) and reaching out to ORE partners across Europe.

Dogger Bank analysis
The Crown Estate map shows the range and diversity of offshore structures. We synthesised the information relevant to acoustic sensing for all offshore renewable energy assets around the UK shore, active, in development and planned. This helped us identify an exemplar site for analysis: Dogger Bank, selected because it is an offshore wind farm in a Marine Protected Area, and because of recent press coverage of Russian vessels visiting North Sea wind farms and taking a close interest in following the routes of subsea power cables. We then used benchmarked and validated acoustic propagation models (from the Acoustic Toolbox User interface and Post processor (AcTUP V2.2L, https://cmst.curtin.edu.au/products/underwater/) to quantify sounds from typical sources (e.g. small ships, submarine vehicles, mammals) and how they are perceived by man-made sensors. This modelling was done over a wide range of frequencies (including the ‘shipping bands’ recommended by the European Marine Strategy Framework Directive and its UK implementation) and for ranges up to 100 km from the exemplar site. The different sound levels, in different frequency ranges, were then translated into sound detection ranges for acoustic sources of interest.

Figure 2 shows one of the many examples, as detection ranges vary with the frequencies of interest (and how they will propagate), with the surrounding bathymetries, and also with the sound speed profiles in different directions around the acoustic sensor (varying with seasons but also with tides, in some cases) and with the signal-to-noise ratios (varying from ‘average’ to ‘optimistic’ cases).

Above: Figure 2: One example of predicted detection ranges for acoustic sources around one ORE structure

UKAN+ funding
Thanks to UKAN+ funding, we were able to strengthen a research team to address the feasibility of building and deploying a marine acoustic sensing network, using the UK archipelago of offshore renewable energy infrastructure. We constrained quantitatively what was achievable in complex and variable environments, and we are now reaching out to different partners across Europe to translate these findings into field measurements and practical applications, helping protect and de-risk ORE assets around Europe.