Mapping seabed habitats in the Firth of Lorn off the west coast of Scotland: evaluation and comparison of habitat maps produced using the acoustic ground-discrimination system, RoxAnn, and sidescan sonar

Abstract

2005. Mapping seabed habitats in the Firth of Lorn off the west coast of Scotland: evaluation and comparison of habitat maps produced using the acoustic grounddiscrimination system, RoxAnn, and sidescan sonar. e ICES Journal of Marine Science, 62: 790e802.In September 2003 a national workshop took place in the United Kingdom with the aim of assessing the accuracy of the acoustic ground-discrimination system (AGDS), RoxAnnÔ, as a tool for mapping seabed habitats in Special Areas of Conservation (SACs). A heterogeneous area of seabed, approximately 1 km 2 in size, was selected for the study. The area was first surveyed using a sidescan-sonar system and a mosaic of the output was produced covering 100% of the survey area. Interpretation of the mosaic identified three acoustically distinct seabed types, the spatial distributions of which were mapped. Four RoxAnn data sets were then collected over the same area of seabed applying different survey parameters (e.g. different survey grids, track spacing, survey vessels, survey speeds, and RoxAnn systems). Extensive ground-truthing was carried out involving 26 drop-down video stations, and from these data six benthic classes (seabed habitats) were identified. Following interpolation of the RoxAnn track-point data to produce full spatial-coverage data, these sixseabed habitat categories were used to conduct supervised classification of the RoxAnn data to produce full-coverage habitat maps of the area for each of the four RoxAnn data sets. Comparisons were then made between the four RoxAnn maps and the sidescan-sonar interpreted map. The accuracy of each map was assessed and the application of this mapping approach for mapping seabed habitats in SACs is discussed.

Predicting spatial kelp abundance in shallow coastal waters using the acoustic ground discrimination system RoxAnn

“…This is a known problem and was already described by e.g. Chivers et al (1990), Collins and Voulgaris (1993), Hamilton et al (1999), andBrown et al (2005).…”

“…Since habitats were very patchy, only distinctly classifiable video sequences were used. The corresponding RoxAnn values that were measured simultaneously during the video survey were averaged over 10 s as recommended by Brown et al (2005) resulting in one E1/E2 value pair for each 10-second sequence. Cross-reference of video data with the acoustic data was achieved via the positioning signal and the time stamp.…”

“…Hamilton et al, 1999;Cholwek et al, 2000;Kenny et al, 2003;Humborstad et al, 2004;Brown et al, 2005;Anderson et al, 2008;Freitas et al, 2011). Since the acoustic scattering process is a complex function of object size, shape, orientation, and material properties as well as acoustic frequency and wavelength (Stanton and Chu, 2000), transfer of approaches from one area or habitat to another is challenging.…”

“…In shallow water, acoustic ground discrimination systems (AGDS) equipped with SBES can provide a high level of seabed discrimination (Brown et al, 2005) and when compared to MBES they are also affordable and easier to operate. However, they should be understood as complementary rather than competing devices (Foster-Smith et al, 2000).…”

Seabed Mapping and Marine Spatial Planning: A Case Study from a Swedish Marine Protected Area

“…A more serious issue is that assemblages may be identified from the in situ data which have no corresponding acoustic class (Freitas et al, 2003). In fact, this is, according to Brown et al (2005), to be expected. The problem is that the spatial detail of the map is limited by the scale at which the acoustic regions are defined, and although boundaries can be modified to a limited extent on the basis of the biotic patterns (which is possible only at a scale defined by the distance between reference sites, i.e.…”