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Environment

One League Under the Sea

   
 
Picture
Launching of Sirene from the afterdeck of the carrier vessel during the ESSIR mission.
In order to analyse and understand the invisible world of the sea bed, oceanographic research uses laboratories which record data at very great depths. Sirene, an autonomous craft, remotely controlled from the surface, is now capable of positioning benthic stations down to depths of as much as 4 500 metres with remarkable precision. A technological achievement in the field of acoustic remote control.

 

Sirene is a craft of four tonnes capable of descending to a depth of 4 500 metres below the surface of the oceans and positioning oceanographic research laboratories operating in a deep-sea environment (known as benthic stations) with remarkable precision. Sirene has no pilot on board and no cable to the surface; it is remote-controlled. "Sirene has no trailing cables, communication is by means of sound waves - hence its name, Sirene, since it responds to an acoustic song," points out Vincent Rigaud, Director of the Deep-Sea Robotics Laboratory of the French Institute of Research into the Exploitation of the Sea (IFREMER). But its name is also an acronym (in French) of its capabilities: European, precision-positioning, remote-controlled, submarine robot.

Autonomous diving
capability Before the creation of this pilot-craft, which can be compared to a submarine space shuttle, stations designed to observe the ocean depths were guided along the sea bed by means of cables, thereby requiring high-tonnage support ships. "A laboratory released in this way can end up anywhere - given the frequent unevenness of this type of terrain," Vincent Rigaud goes on to explain. "Consequently, it is then necessary to send out a submersible - crewed or remotely operated and equipped with handling gear - in order to position the platform at the required spot. The operation is laborious, costly in time and the deployment of vessels, and lacking in precision. Nowadays Sirene is carried by a single oceanographic vessel, some 60 metres in length. Once in the sea, with the laboratory secured to it, it descends to the sea bed with the help of an integrated advanced navigation system enabling it to pinpoint its position with impressive accuracy - to within a few metres."

Once it has reached the desired spot, much like a fork-lift truck, Sirene sets down the observation station. Its movements can be monitored continuously by teleacoustics and remote control. Having completed its task, the craft resurfaces "under its own steam".

Picture
A concept not solely of interest to the scientists, but potentially useful to the offshore sector as well .

Teleacoustic capability
Sirene is a light prototype, small in size (4.2 metres long), capable of shifting a load of 10m3 weighing some 3.5 tonnes, and is equipped with two computers enabling its descent to be managed, in real time, with extreme precision. This robot of the ocean deeps is the result of a European research incentive in the framework of the Desibel project (New methods for deep sea intervention on future benthic laboratories, analysis, development, engineering and tests) under the MAST II Programme. The acoustic transmissions, navigation and control system were the work of the French scientific and technological organisation IFREMER, the coordinator of the project. The mechanical and electrical integration were achieved with the help of COMEX Technologies (Marseilles, France), which has been entrusted with the mechanical design and has played a coordinating role in integrating all the component elements. The on-board computers to manage the command and control system were supplied by the Lisbon Instituto Superior Técnico (IST) and the aluminium structure by the Technical University of Berlin, which also conducted the hydrodynamic tests, on a mock-up, in its testing tank.

To the nearest metre
The prototype already has some 20 descents to its credit, one of them to a depth of 2500 metres. Its existing propulsion systems - the performance of which could easily be improved - enable it to descend to 4500 metres, and its acoustic teletransmission system, which is particularly powerful, allows it to be guided from a distance of 9 km. Sirene has been designed to put down a wide variety of stations, such as SAMO, which belongs to IFREMER. Under the MAST II DESIBEL project it put down, by way of demonstration, a load simulating a benthic station to a depth of 2500 metres.

"These stations designed to take physico-chemical measurements are bristling with instruments. In certain cases, cameras can send images to oceanographic vessels waiting at the surface, directly above the station, by various acoustic teletransmission systems," explains the IFREMER official in charge. "The main attraction of these benthic laboratories lies in the fact that they stay put at a precise point for long periods, thereby enabling the scientists to study the phenomena over time."

Sirene is not intended to be used solely by researchers. As Vincent Rigaud points out, "The concept can be employed in other areas, for instance in relation to offshore prospecting and exploration. Oilmen, too, when they operate equipment on the sea bed, traditionally work with cable equipment - Remotely Operated Vehicles (ROVs) - which can descend to 1000 metres. However, new discoveries in West Africa indicate that there are sites to be investigated down to a depth of 2500 metres. Under these conditions, operational constraints associated with cable mean that surface vessels supporting the ROVs would need to be larger in size. Unattached craft operated by acoustic remote control, such as Sirene, could be used as an economically viable alternative."

 

 

Project Title:  
SIRENE.
This project forms part of DESIBEL (New methods for deep sea intervention on future benthic laboratories, analysis, development, engineering and testing)

Programmes:
MAST II

Contract Reference:
MAS20082

CORDIS databaseFor more information on this project,
go to the Cordis database Record

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