engleski

Marine biological research with the help of micro remote operating vehicle (ROV)

Diving is essential for the research of benthic organisms and communities living on the hard substrata in the sea. However, due to human physiology in situ research under the sea is limited in time and space as well as technically very complex. Small, therefore affordable, unmanned remotely operated vehicles (ROV) could play important role in undersea biological research. They should be movable and flexible in order to be suitable for replacing man in prolonged diving and at greater depths. Nevertheless, careful planning of ROV configuration and considerable effort in its adjustment are essential for good results. Scope: In order to test the possibilities and reaches we performed two preliminary common missions – biologists-divers and VideoRay® ; ; ROV: in June 2006 in the Natural Park Telašćica, Dugi otok, and in May 2007 in Ždrelac Strait, between Ugljan and Pašman Islands, both in the Middle Adriatic. The tasks were: 1 - to test ROV performance in a narrow submarine cave ; 2 - to check a possibility of mapping the endangered sea-grass Posidonia oceanica meadow with an ROV ; 3 - to make a video survey along a positioned diving transect. Experimental results and discussion: Task 1. With the physical help of SCUBA divers ROV was escorted to the cave entrance at 24 m and lowered into the cave chamber at 31 m depths (inaccessible to divers) in order to inspect chamber walls for the presence of little carnivorous sponge Asbestopluma hypogea, which lives at the cave entrance. On the ROV video recording it was possible to clearly see the surface of the rock inside the chamber but the sponges were not noted. The narrowness of the passage and roughness of the surface resulted in hitching and hooking of ROV cable - divers presence showed to be very important during ROV retrieval. Also, diver lowered ROV through narrow shaft - ROV propulsion was deliberately turned off not to endanger fragile sponges. Task 2. The ROV was lowered to the sea bottom in the area of Telašćica Natural Park with the known Posidonia meadow. Due to fairly good visibility it was possible to record lower border of the meadow at little deeper than 20 m and the general direction in which it extends. However, it was not possible to precisely map the extent of the meadow without underwater positioning system. Also, we encountered a problem with the ROV cable positive buoyancy: it was not possible to properly control the ROV when length of cable in the water exceeded 20 m. Task 3. In the shallow area of Ždrelac Strait (approx. 3 m of depth) the ROV was driven along the 200 m long diving transect (5 mm thick white rope with distance flags), positioned at the bottom by divers, in order to record organisms and habitats. Although visibility was not good it was possible to recognize habitats. However, ROV camera resolution was not good enough for species determination along the diving transect. At that time another ROV cable were used and we encountered the problem of its negative buoyancy: the cable got hitched on the bottom obstacles like big fan shells (Pinna nobilis). Divers’ presence was very helpful in such occasions. Conclusions: On the basis of presented preliminary work it is obvious that micro ROVs can be very helpful in the marine biological research, especially of benthos on the hard substrata, where short divers bottom time is a limiting factor. However, high-resolution standard of digital camera, appropriate amount of light (flash lamps), possibility of focusing in wide range of focal points are prerequisite for recognition of organisms. Also, for the recording of spatial distribution of species/communities and e.g. retrieval of data loggers it is necessary that ROV is equipped with underwater positioning system for precise positioning. For data loggers (for temperature, light, pressure, etc. recording) positioning and retrieval as well as for biological sampling configuration and control of manipulators are demanding. Even when all the technical prerequisites are fulfilled it is still necessary to put considerable time and effort into the adjustment in the field. During that time a synergistic action of diver(s) and ROV are necessary.

In situ submarine research ; new technologies ; synergistic action man-ROV

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