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Undersea moorings recovered after 13 years of submersion thanks to Argos

Dec 6, 2016

In February 2016, Jean-Louis Lamy (from LAMY Marine Consulting) was tasked with recovering four subsurface moorings off Crozet Island, that had been deployed more than 13 years ago. The moorings, located at 400 meters below the sea surface,  were equipped with Argos beacons to facilitate recovery when surfacing.

For the 1st mooring, the team headed to the area with a sounder to locate it and “unhook” it from the seabed. Once the material was recovered, it’s acoustic release mechanism and Argos beacon proved to be still functional. Therefore, it was decided to program the release of the three other moorings (by acoustic signal) and recover them with the ARGOS RXG-134 Goniometer.

The mission took place on board of the Marion Dufresne, with the goniometer’s antenna installed on the ship’s bridge, thanks to the 25 m extension cable. The mooring’s release was programmed, and the 2nd mooring quickly rose to the surface. The Argos tag worked immediately, allowing the team to retrieve the equipment using the Goniometer. The 4th mooring was recovered in the same way.

Argos equipment

Photo Courtesy of Jean-Louis Lamy

On the other hand, the 3rd mooring did not come up to the surface immediately, certainly due to fouling issues after 13 years of immersion. It took 24 hours for the 1st Argos signal to be received by the Goniometer, while the equipment drifted further and further from its mooring zone. The Goniometer was a crucial component of the recovery effort, providing an angle and a signal intensity which eventually led to the recovery of the equipment, despite the low battery level of the beacon, which made it impossible for the satellite to receive any signal.

The mission was a success, with the complete  recovery of all the equipment. This story testifies to the Argos beacons (and system’s) robustness, still functional after 13 years of immersion in the Southern Indian Ocean, and to the Goniometer’s critical role in recovering the material.

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