Publication Abstract

Developing a strategy for seabed mapping at different spatial scales and resolutions: case study of seabed characterisation in an area of the eastern English Channel

Developing a strategy for seabed mapping at different spatial scales and resolutions: case study of seabed characterisation in an area of the eastern English Channel

R.A. Coggan, S. Philpott, D.S. Limpenny and W.J. Meadows

As part of a larger study of the role of seabed mapping techniques in environmental monitoring and management, acoustic surveys were made at a study site in the eastern English Channel with the aim of developing a strategy for mapping at different spatial scales. The site comprised a broad scale area (40 x 15 km) between Dungeness and Hastings, within which was nested a smaller study box (4 x 12 km), containing an area licensed for aggregate extraction. During a previous investigation, a basic (low resolution) interpretation was made of 100% sidescan coverage of the smaller study box, recognising four acoustically distinct areas, which were ground-truthed and classified as four distinct biotopes. The present study made a more detailed (high resolution) interpretation of the same sidescan mosaic, recognising nine different seabed facies and mapping the area into ~20 regions. Each of the original acoustically distinct areas contained multiple seabed facies, accounting for the high variability between replicate ground-truth samples noted during the initial study. Consequently, the site was re-visited to ground-truth the seabed facies map. Results of that ground-truthing are presented, and comparisons made between the low- and high- resolution characterisations of the seabed. Within the broad scale study area, a foundation pattern of sidescan lines spaced at 2 km intervals has gradually been augmented with additional ‘in-fill’ lines to achieve progressively greater density of sidescan coverage. The relationship between density of acoustic coverage and confidence in interpreting broad scale patterns and features is explored. Strategies for mapping at different spatial scales are discussed.

Reference:

R.A. Coggan, S. Philpott, D.S. Limpenny, W.J. Meadows and S.E. Boyd. 2004. Developing a strategy for seabed mapping at different spatial scales and resolutions: case study of seabed characterisation in an area of the eastern English Channel. ICES ASC, Vigo, Spain, 2004.  ICES CM2004/T:04.

R.A. Coggan*, S. Philpott, D.S. Limpenny* and W.J. Meadows*

ICES Copenhagen. ICES CM 2004/T:04