Satellite detection and mapping of sandbank crests: supporting location of offshore wind developments and conservation areas

Project Description:

This PhD aims to contribute to the field of seabed mapping, by developing novel methods combining satellite bathymetry and turbidity modelling, to deliver improved understanding of spatial and temporal benthic variability, establishing the potential for OWF development within a dynamic protected habitat.

The North Sea’s reliable source of wind power, relatively shallow waters and proximity of developed energy markets have attracted significant offshore renewable energy development. Now highly occupied, efficient management of offshore space is essential if further large-scale deployments are to be realised and ambitious 2030 and 2050 energy goals achieved. The planning process has not been straightforward, in part due to spatial conflicts with existing users and protected areas, but use of offshore space remains less contentious than onshore development and as such is often perceived as the most viable option for scaling up the deployment of energy infrastructure.

Significant infrastructure now exists within North Sea protected areas and further developments are proposed. If co-location options are to continue to support the urgent prioritisation of deployment, enhanced understanding of proximate protected habitats is required to inform environmental impact assessments and support ongoing monitoring.

Sandbank habitats are protected under the EU Habitats Directive and UK Conservation of Habitats and Species (Amendment) (EU Exit) Regulations 2019. Such soft substrates are sought-after for development, and since strong tidal currents could ensure sandbanks be replenished and recover relatively rapidly, they exhibit co-location potential as they are considered only moderately sensitive to seabed disturbance. Their mobile nature may ensure that habitat functions remain relatively resilient, but this is poorly understood to-date. Extensive, repetitive offshore bathymetric surveys required to yield information on sandbank dynamics are prohibitively expensive using vessel-mounted acoustics, while mobility and associated turbidity have presented challenges to monitoring using satellite derived bathymetry.

Multispectral satellite imagery can yield bathymetric data via wavelength-dependent rates of light attenuation in water.  Empirical models use ground truth data, e.g. from acoustic surveys, to establish the relationship between depth and the ratio of reflectance values of different band combinations. Methods are effective in clear tropical waters, prediction accuracy decreasing with increasing depth. But turbidity, mobility and spatial variability present additional challenges in dynamic temperate environments. This project builds on promising pilot work, conducted by JNCC and Newcastle University 2019-20, to evaluate the feasibility of using Sentinel-2 imagery to detect sandbank crests in Special Areas of Conservation (SACs) off the east coast of England. Proof of concept was achieved, but further work is required to develop a consistent process, potentially enabling monitoring dynamic processes over decadal timescales, and quantification of responses to anthropogenic impacts.

Acoustic multi-beam (MBES) data collected by Cefas in 2016 described the crests of the submerged sandbank designated features in three Special Areas of Conservation (SACs) offshore from North Norfolk (-10 to -18m). These data will be used validate bathymetric models from 2016 Sentinel-2 imagery for application to time-series of these data (2015-present). Understanding of natural sandbank dynamics modelled from satellite-derived bathymetry (SDB) can then be applied to existing and proposed offshore developments, for example, where transmission to Race Bank OWF passes through Inner Dowsing SAC, and where agreements for transmission to Norfolk Vanguard and Boreas sites may affect North Norfolk Sandbanks SAC, supporting improved assessment of anthropogenic impacts to dynamic habitats.