Marine bird foraging around headlands in tidal streams

HydrodynamicsAbstrac

3D modelling of upwelling around a headland

Hydrodynamic

A review of unmanned aerial vehicles usage, as an environmental survey tool, within tidal stream environments

Funding Information: This work was funded by the Bryden Centre project, supported by the European Union’s INTERREG VA Programme and managed by the Special EU Programmes Body (SEUPB). The views and opinions expressed in this paper do not necessarily reflect those of the European Commission or the Special EU Programmes Body (SEUPB). Aspects of this research were also funded by a Royal Society Research Grant (RSG\R1\180430), the NERC VertIBase project (NE/N01765X/1), the UK Department for Business, Energy, and Industrial Strategy’s offshore energy Strategic Environmental Assessment programme and EPSRC Supergen ORE Hub (EP/S000747/1).Peer reviewe

Using Unmanned Aerial Vehicle (UAV) Imagery to Characterise Pursuit-Diving Seabird Association With Tidal Stream Hydrodynamic Habitat Features

Acknowledgments We gratefully acknowledge the support of colleagues at Marine Scotland Science, the crew and scientists of the MRV Scotia 2018 cruise (particularly Chief Scientist Adrian Tait) and ERI interns: Gael Gelis and Martin Forestier. We gratefully acknowledge the constructive comments from reviewers. Finally, we also want to thank Ella Benninghaus for providing the auk illustrations used within the paper. Funding This work was funded by the Bryden Centre project, supported by the European Union’s INTERREG VA Programme, and managed by the Special EU Programmes Body (SEUPB). The views and opinions expressed in this paper do not necessarily reflect those of the European Commission or the Special EU Programmes Body (SEUPB). Aspects of this research were also funded by a Royal Society Research Grant [RSG\R1\180430], the NERC VertIBase project [NE/N01765X/1], the UK Department for Business, Energy, and Industrial Strategy’s offshore energy Strategic Environmental Assessment programme and EPSRC Supergen ORE Hub [EP/S000747/1].Peer reviewedPublisher PD

Surface Characterisation of Kolk-Boils within Tidal Stream Environments Using UAV Imagery

Funding: This work was funded by the Bryden Centre project, supported by the European Union’s IN- TERREG VA Programme, and managed by the Special EU Programmes Body (SEUPB). The views and opinions expressed in this paper do not necessarily reflect those of the European Commission or SE- UPB. Aspects of this research were also funded by a Royal Society Research Grant [RSG\R1\180430], the NERC VertIBase project [NE/N01765X/1] and the UK Department for Business, Energy and Industrial Strategy’s offshore energy Strategic Environmental Assessment programme. Data Availability Statement The data underlying this article will be shared on reasonable request to the corresponding author. Acknowledgments We gratefully acknowledge the support of Julien Martin, colleagues at Marine Scotland Science and the crew and scientists of the MRV Scotia 2016 and 2018 cruises (particularly Chief Scientists Eric Armstrong and Adrian Tait). We also acknowledge the work contributed by ERI interns: Gael Gelis and Martin Forestier.Peer reviewedPublisher PD

Colour Sonar: Multi-Frequency Sidescan Sonar Images of the Seabed in the Inner Sound of the Pentland Firth, Scotland

The backscatter response of a seabed to an incident sonar signal is dependent on the carrier wave frequency: i.e., the seabed is acoustically colourful. Colour is implemented in a prototype three-frequency sidescan sonar system deployed in the Pentland Firth, north Scotland. Sonar amplitude data as a function of frequency are processed to render them an unconfounded effect of the seabed normalized to the response at a reference inclination angle, for colour to be a meaningful property of the seabed. Methods for mapping data at sonar frequencies to optical primary colours for human visualisation are explored. We recommend methods that in our opinion generate colour characteristics harmonious with human vision in which: shadow is white; saturation black; colour shade darkness is proportional to backscatter strength; and shades of red, green and blue are seen in proportion to the backscatter amplitudes of the low-, mid- and high-frequency sonar data. Frequency equalisation is applied to achieve a balance in colour responses in images. The seabed in the survey area is acoustically colourful. Using the “negative BGR” colour mapping method: a weakly backscattering sand dune in the north of the survey area appears as shades of light blue and purple; a strongly backscattering halo of cobbles around the dune appears as shades of hazel brown; a strongly backscattering gravel ridge across the south of the survey area appears as shades of royal blue; and exposed rock as textures ranging in colour from light brown to light blue/green. There is evidence for colour anisotropy (a dependence of colour on the direction of ensonification). Similarities between anthropic colour sonar and the natural sonar of Microchiropteran bats are noted. Bats’ sonar satisfies the information criteria for acoustic colour, and it is hypothesized that it informs a colourfully-perceived world view

Numerical Simulations of the Effects of a Tidal Turbine Array on Near-Bed Velocity and Local Bed Shear Stress

We apply a three-dimensional hydrodynamic model to consider the potential effects of energy extraction by an array of tidal turbines on the ambient near-bed velocity field and local bed shear stress in a coastal channel with strong tidal currents. Local bed shear stress plays a key role in local sediment dynamics. The model solves the Reynold-averaged Navier-Stokes (RANS) equations on an unstructured mesh using mixed finite element and finite volume techniques. Tidal turbines are represented through an additional form drag in the momentum balance equation, with the thrust imparted and power generated by the turbines being velocity dependent with appropriate cut-in and cut-out velocities. Arrays of 1, 4 and 57 tidal turbines, each of 1.5 MW capacity, were simulated. Effects due to a single turbine and an array of four turbines were negligible. The main effect of the array of 57 turbines was to cause a shift in position of the jet through the tidal channel, as the flow was diverted around the tidal array. The net effect of this shift was to increase near-bed velocities and bed shear stress along the northern perimeter of the array by up to 0.8 m·s−1 and 5 Pa respectively. Within the array and directly downstream, near-bed velocities and bed shear stress were reduced by similar amounts. Changes of this magnitude have the potential to modify the known sand and shell banks in the region. Continued monitoring of the sediment distributions in the region will provide a valuable dataset on the impacts of tidal energy extraction on local sediment dynamics. Finally, the mean power generated per turbine is shown to decrease as the turbine array increased in size

On the Information Advantage of Sidescan Sonar Three-Frequency Colour over Greyscale Imagery

A prototype three-frequency (114, 256, and 410 kHz) colour sidescan sonar system, built by Kongsberg Underwater Mapping Ltd. (Great Yarmouth, UK), was previously described, and preliminary results presented, in Tamsett, McIlvenny, and Watts. The prototype system has subsequently been modified, and in 2017, new data were acquired in a resurvey of the Inner Sound of the Pentland Firth, North Scotland. An image texture characterisation and image classification exercise demonstrates considerably greater discrimination between different seabed classes in a three-frequency colour sonar image of the seabed, than in a multi-frequency colour image reduced to greyscale display, or in a single-frequency greyscale image, with readily twice the number of classes of seabed discriminated between, in the colour image. The information advantage of colour acoustic imagery over greyscale acoustic imagery is analogous to the information advantage of colour television images over black-and-white television images. A three-frequency colour sonar image contains a theoretical maximum of a factor of 3 times the information in a corresponding greyscale image, for independent seabed responses at the three frequencies. Estimates of the average information per pixel (information entropy) in the colour image, and in corresponding greyscale images, reveal an actual information advantage of colour sonar imagery over greyscale, to be in practice approximately a factor of 2.5, empirically confirming the greater information based utility of three-frequency colour sonar over greyscale sonar. Reference: Tamsett, D.; McIlvenny, J.; Watts, A. J. Mar. Sci. Eng. 2016, 4(26)