The use of sidescan sonar to compliment environmental data in conjunction with Cornish Wave Hub site

A transect line of approx. 19km in a south to north direction was established at a distance of approx. 1.5 – 1.8km east from the boundary of the Cornish WaveHub site and approx. 9km north of the shoreline. The transect crossed two coastal shelf‟s the first situated at the southern extent of the survey area at approx. 26m water depth, the second midway through the survey extent descending to 45m water depth and over the shelf onto the northern extent of the survey reaching 59m water depth. Using a GeoAcoustics 159d sidescan sonar fish operating at 400 kHz two survey lines where run at 75m line spacing over this transect line. Previous environmental measurements investigating the current turbidity properties of the area had been made the week prior to this survey along the same transect. The main aim of this study was to provide high resolution imagery and an in-depth analysis of the underlying seabed features to support the future analysis of the environmental measurements which had been made. This was achieved through analysis and processing of the raw sidescan waterfall imagery using CODA software and then further processing of the data into a mosaic which was then geographically displayed and presented as a series of charts with the use of ArcGIS software. A manual seabed classification scheme was developed and the imagery was classified into areas of similar intensities and textures of backscatter to provide a habitat map of the area using visual interpretation and ArcGIS software. An additional approx. 2.6 km single survey line was established to the west of the 19km transect for the purpose of identifying some previously deployed survey apparatus which had been moored on the seabed. Linear rock formations orientated in a SSW - NNE direction and corridors for sediment transport from shallow to deep were observed to be characteristic of the shallower southern extents of the survey area. As depth decreased larger rocky outcrops, sparse boulders and the presence of sediment ripples indicating a hydrodynamically controlled environment was apparent. The survey requires regular ground truthing to validate findings. It is recommended that future studies should investigate a wider corridor and the validity and accuracy of the survey would benefit from the use of an Automatic Classification Scheme