Monitoring of red coral (Corallium rubrum) populations in Parc National des Calanques (Marseille), five years after the initial inspection.
Observations beyond 50 m depth south of the island of Riou and in the Cassidaigne Canyon, from the ROV APACHE and the very high definition underwater photogrammetry system ORUS 3D
Within the scope of the monitoring of red coral (Corallium rubrum) populations in the Parc National des Calanques (off Marseille), the Marine and Innovation Departments of COMEX SA carried out underwater surveys beyond 50 meter depth, using an ROV (Remotely Operated Vehicle) equipped with video and still cameras together with a photogrammetric system, ORUS 3D, developed and operated by COMEX Innovation. Operations at sea were carried out on February 5 and 6, 2019 using JANUS II, COMEX catamaran DP support vessel.
The purpose of the mission was to come back five years after the initial inspection at locations where populations of red coral are growing, close to RIOU Island and in the CASSIDAIGNE submarine canyon featuring uneasy access to divers, in order to conduct quantitative and qualitative evaluations using an ROV. Operation of ORUS 3D results in millimetric accuracy measurements of coral colonies. Such datas are nearly impossible to collect using ordinary stills camera or /and laser pointers. This innovative technology provides scientists with new biometric data of deep red coral populations.
ORUS 3D photogrammetry system mounted on the Comex ROV Apache
ORUS 3D is an optical system that may be interfaced with all types of submarine vehicles. Based on the photogrammetry technology, the system features three very high trifocal resolution sensors synchronized with and operated from a surface control unit located onboard the support vessel. Led lighting flashes provide an optimal lighting of the scenery. A contact free and non-intrusive measurement tool, the system provides a 3D high resolution modeling of substructures and seascapes, reaching submillimetric details and millimetric accuracy.
ORUS 3D very high definition photogrammetry system
3D modeling of acquisitions
3D model of a rock at 70 m depth, sheltering red coral
Selected inspection areas feature the south, south-east side of RIOU Island and the north-east and north-west heads of the CASSIDAIGNE Canyon. The southern part off RIOU Island had been surveyed back in 2013 as initial inspection site. These sites feature rock blocks positioned between 50 msw and 70 msw. CASSIDAIGNE north western head is a renown site, already surveyed by COMEX during scientific campaigns : HERMES (2009) for the german MARUM laboratory ; MEDSEACAN (2009) and “Grottes et Canyons 3D”- Underwater 3D Caves and Canyons – (2014)for the French Agence des Aires Marines Protégées (AAMP) – now Agence Française pour la Biodiversité. The inspected sites range from 200 msw down to 250 msw. Ultimately, the CASSIDAIGNE north-eastern zone was a brand new site, never explored yet. It turned out to be very rich in red coral colonies.
Using COMEX sophisticated logistics in terms of positionning, sites that had been previously inspected were easily relocated. Moreover, with the help of bathymetric datas and the use of the Apache ROV Sonar, a new red coral spot has been discovered at 240 msw in the CASSIDAIGNE north-eastern zone. Last but not least, 3D modeling datas are now being processed. They will soon prove to be a superb tool that will optimize our knowledge of the deep red coral populations.
