Abstract
Vertical walls in marine environments can harbour high biodiversity and provide natural protection from bottom-trawling activities. However, traditional mapping techniques are usually restricted to down-looking approaches which cannot adequately replicate their 3D structure. We combined sideways-looking multibeam echosounder (MBES) data from an AUV, forward-looking MBES data from ROVs and ROV-acquired videos to examine walls from Rockall Bank and Whittard Canyon, Northeast Atlantic. High-resolution 3D point clouds were extracted from each sonar dataset and structure from motion photogrammetry (SfM) was applied to recreate 3D representations of video transects along the walls. With these reconstructions, it was possible to interact with extensive sections of video footage and precisely position individuals. Terrain variables were derived on scales comparable to those experienced by megabenthic individuals. These were used to show differences in environmental conditions between observed and background locations as well as explain spatial patterns in ecological characteristics. In addition, since the SfM 3D reconstructions retained colours, they were employed to separate and quantify live coral colonies versus dead framework. The combination of these new technologies allows us, for the first time, to map the physical 3D structure of previously inaccessible habitats and demonstrates the complexity and importance of vertical structures.
Highlights
Habitat structural complexity may have a profound effect on ecological interactions[1]
AUVs can provide higher resolutions than ship-mounted systems in many deep-water environmental settings
Using Structure from Motion’ (SfM), we were successful in recreating large portions of the acquired video footage as georeferenced 3D renditions, where individual organisms/colonies could be positioned in 3D space (Figs 4 and 5)
Summary
Habitat structural complexity may have a profound effect on ecological interactions[1]. Related photogrammetry techniques such as ‘Structure from Motion’ (SfM), an approach that allows 3D models to be reconstructed from overlapping images of a single moving camera, are being employed to build high-resolution digital elevation terrains of such reefs[17,18,19] and representations of single coral colonies at such fine resolutions that individual polyps can be reconstructed[20]. From these techniques, high-resolution coloured point clouds are produced, georeferenced, scaled, and used for morphometric measurements as well as to derive fine-scale terrain metrics. AUVs can provide higher resolutions than ship-mounted systems in many deep-water environmental settings
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