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

Tamsett, Duncan; McIlvenny, Jason; Watts, Andrew

doi:10.3390/jmse4010026

Cited by 19 publications

(27 citation statements)

References 22 publications

(30 reference statements)

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“…Hence, it is not possible to derive band ratios or exploit spectral signatures. The potential for improved seafloor classification with 3-band acoustic backscatter data has recently been demonstrated (Hughes-Clarke, 2015;Tamsett et al, 2016) and it is hoped that multi-spectral MBES will become the standard in seafloor mapping.…”

Section: Discussionmentioning

confidence: 99%

Application of Geobia to map the seafloor

Diesing

2016

GEOBIA 2016: Solutions and Synergies

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ABSTRACT:Geographic Object-Based Image Analysis (GEOBIA) has been successfully employed to map terrestrial environments. However, 71% of Earth's surface is covered by seawater and standard optical methods suitable for mapping the land surface have limited application in such environments. Application of GEOBIA to marine environments has nevertheless been attempted and can generally be subdivided into three domains: 1. The intertidal zone and shallow subtidal zone have been mapped with optical data and application of GEOBIA in such environments can be seen as a seaward extension of terrestrial approaches. 2. Photographs of the seafloor give very detailed but spatially limited information. GEOBIA methods have been applied to classify benthic species and habitats and estimate seafloor complexity among others. 3. Due to the rapid attenuation of light in water, the method of choice to map the seafloor employs sound. Modern multi-beam echosounders map the seafloor in high detail. Such sensors measure the topography (water depth) and the strength of the returning signal (backscatter), which can be used to characterise the seafloor substrates and habitats. This contribution will focus on the application of GEOBIA to marine acoustic datasets. A generic workflow for object-based acoustic seafloor mapping will be showcased and the current state of the application of GEOBIA to marine acoustic data will be discussed.

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Section: Discussionmentioning

confidence: 99%

Application of Geobia to map the seafloor

Diesing

2016

GEOBIA 2016: Solutions and Synergies

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“…Water depths in the Inner Sound reach about 36 m in the central channel. Shields et al [4] described the Pentland Firth as comprising predominantly of exposed bedrock, but localised sediment and shell deposits around Stroma have been mapped in recent years [3,11,12]. An oval-shaped sediment bank lies immediately to the south of Stroma, and a wedge-shaped bank of shell fragments lies just adjacent to the main flow through the channel (Figure 1).…”

Section: Study Sitementioning

confidence: 99%

“…Fairley et al [9] combined a variety of data to construct a map of sediment type through the Pentland Firth and surrounding area, but detail in the Inner Sound was limited. Information on local sediment distributions in the Inner Sound is gradually being accumulated through multibeam [3] and sidescan sonar surveys [11,12]. Sediment banks are known to lie to the south of the island of Stroma (Figure 1) but the local sediment dynamics, and the potential impacts of tidal energy extraction on the deposits, are only beginning to be understood.…”

Section: Introductionmentioning

confidence: 99%

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

Gillibrand

Walters²,

McIlvenny

2016

Energies

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Abstract: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.

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“…All of these effects need to be compensated for in order for the raw acoustic amplitude recorded by a sonar system to be reduced to an effect of the seafloor alone unaffected by anything else. This is particularly important in multi-spectral sidescan sonar imaging, in which seabed acoustic response as a function of frequency is represented by color, in order for acoustic color to be an effect of the seabed unaffected by other factors (Tamsett et al [7,8]). In the current paper, only the effect of geometrical spreading is considered further.…”

Section: Introductionmentioning

confidence: 99%

Geometrical Spreading Correction in Sidescan Sonar Seabed Imaging

Tamsett

2017

JMSE

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Sound backscattered to a sonar from a seabed decreases in intensity with increasing range (R) due to geometrical spreading. As a far-range approximation, a geometrical spreading correction of +30 log R decibels may be applied. A correction based on an accurate estimation of the area of the seabed ensonified by the sonar pulse incorporates additional terms that are a function of: range, sonic ray inclination angle, along-and across-trace components of seabed slope and sonar vehicle pitch. At near-normal incidence, the area of the seabed ensonified by the pulse lies within a circle truncated by the narrowness of the sonar beam. Beyond a critical range, the ensonified area separates into two areas disposed on opposite sides of an annulus, one being the principal and the other its conjugate. With increasing range, backscatter intensity from the conjugate area rapidly decreases. At steep inclination angles, the principal area of seabed ensonified is effectively increased by an estimable factor due to scattering from the conjugate area. Backscatter from the conjugate area leads the angle of incidence measured by swath interferometry requiring a correction for an estimate of the angle to the center of the pulse in the principal area.

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

Cited by 19 publications

References 22 publications

Application of Geobia to map the seafloor

Application of Geobia to map the seafloor

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

Geometrical Spreading Correction in Sidescan Sonar Seabed Imaging

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