Using ROV video photogrammetry to reconstruct seafloor landforms of Arctic cold seep environments

Cold seeps are locations on the seafloor where reduced compounds from subsurface hydrocarbon reserves enrich sediment fluids or emanate freely as gas from the seabed. Associated with these spots, numerous underwater landscapes and various chemosynthetic communities were uncovered during the last decades of seafloor exploration. 

Arctic cold seeps offshore Svalbard were explored using Ægir6000, a work-class ROV (Remotely Operated Vehicle) equipped with three HD video cameras that filmed the ocean floor at different angles. The ROV, moving at a constant speed of 1 knot, followed predefined routes to guarantee optimal lateral overlap between adjacent transects. From the videos of the nadiral camera, a photogram every two seconds was automatically extracted. Then, the images were processed in Agisoft Metashape® following a well-established photogrammetry workflow. As final outputs, we obtained 3D mesh, orthomosaics and DTMs at ultra-high-resolution (mm) allowing us to obtain detailed morphometric maps.

These data allowed us to reconstruct accurate georeferenced 3D models representing a variety of small-scale (sub-cm) seabed features and provide essential information for a better understanding of the spatial pattern associated with submarine biogeochemical and physical processes at the seafloor. Moreover, the realized models present the locations where push corers were collected. This correspondence will allow us to integrate fine-scale habitat mapping and pore fluid datasets to quantify the areal methane fluxes.

This work was supported by the Research Council of Norway, for AKMA - Advancing Knowledge on Methane in the Arctic, project number 287869.

Keywords: Submarine geomorphology, ROV, Underwater 3D Photogrammetry, optical 3D models, Cold Seeps, Arctic Ocean