New approaches to high-resolution mapping of marine vertical structures

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

Design of optical instrumentation for 3D and temporal deep-sea observation

In this paper, we present two innovative optical systems dedicated to deep sea observation. The instrumentation and associated methodology are developed in the context of European project EXOCET/D (FP6-GOCE-CT-2003-505342, http://w3.ifremer.fr/exocetd) [SAR04]. The general objective of the project focuses on the design, the implementation and the test of specific instruments to explore, study and quantify biodiversity in the deep sea. The relationship between habitats and environmental dynamics is also an important issue of the project. The presented development takes benefit of work carried out at Ifremer for several years in the field of underwater imaging and measurement [CAD04].One specific target is to set up a complete methodology to make a 3D reconstruction of small scale scenes using stereovision techniques. To meet this scientific requirement, a new system, called IRIS (Invariant 3D Reconstruction by Instrumented Stereovision), has been specified and is under development. It includes the design of a stereovision head and the associated methods for data processing.For an operational use in an underwater environment, the stereovision head will be operated by Ifremers deep scientific Remotely Operated Vehicle victor 6000. The ROV is landed on the seafloor to keep a fixed and stable attitude, a small region of interest (around 1m3) is investigated by the stereovision rig mounted at the tip of victor 6000s instrumented robotic arm MAESTRO