Seafloor monitoring west of Helgoland (German Bight, North Sea) using the acoustic ground discrimination system RoxAnn

Christian.Hass [ at ]


Marine habitats of shelf seas are in constant dynam- ic change and therefore need regular assessment particularly in areas of special interest. In this study, the single-beam acoustic ground discrimination system RoxAnn served to as- sess seafloor hardness and roughness, and combine these pa- rameters into one variable expressed as RGB (red green blue) color code followed by k-means fuzzy cluster analysis (FCA). The data were collected at a monitoring site west of the island of Helgoland (German Bight, SE North Sea) in the course of four surveys between September 2011 and November 2014. The study area has complex characteristics varying from out- cropping bedrock to sandy and muddy sectors with mostly gradual transitions. RoxAnn data enabled to discriminate all seafloor types that were suggested by ground-truth informa- tion (seafloor samples, video). The area appears to be quite stable overall; sediment import (including fluid mud) was de- tected only from the NW. Although hard substrates (boulders, bedrock) are clearly identified, the signal can be modified by inclination and biocover. Manually, six RoxAnn zones were identified; for the FCA, only three classes are suggested. The latter classification based on ‘hard’ boundaries would sufficefor stakeholder issues, but the former classification based on ‘soft’ boundaries is preferred to meet state-of-the-art scientific objectives.

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DOI 10.1007/s00367-016-0483-1

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Hass, H. C. , Mielck, F. , Fiorentino, D. , Papenmeier, S. , Holler, P. and Bartholomä, A. (2016): Seafloor monitoring west of Helgoland (German Bight, North Sea) using the acoustic ground discrimination system RoxAnn , Geo-Marine Letters . doi: 10.1007/s00367-016-0483-1

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