Category: ANFOG, Home Slider, WA-IMOS, Q-IMOS
Now you see it, now you don't. The case of the disappearing glider – solved.
Sometimes having a back-up plan pays dividends, as demonstrated by a recent ‘cat and mouse’ chase through the Torres Strait in search of a wayward ocean glider.
A glider deployed in the Coral Sea in May this year developed technical problems, most likely due to a faulty memory card which did not allow for writing any data. Deployed to gather data in an area of the coastal shelf/slope where there are substantial gaps in our knowledge of marine conditions, the glider was cut off from communications with researchers. Without the guidance of a pilot, the glider had become adrift at the surface in the system of currents.
Planning ahead for just such technical malfunctions, researchers at the IMOS Ocean Glider facility had installed a back-up ARGOS tracking system on the glider. Using technology generally applied for tracking marine animals such as sharks, the gliders were fitted with transmitters that would emit signals that could be detected by an array of satellite receivers.
The position data is received by the IMOS satellite receiving system located at the Australian Institute of Marine Science (AIMS) in Townsville. The data is sent in near real time to CNES CLS in France for distribution to users.
These receivers were able to detect the location of the glider as the satellites passed overhead. The path was difficult to follow as the signals from the glider were only being detected intermittently, as it was entrained into several eddies close to Papua New Guinea. However, this was enough information for Dennis Stanley from the University of Western Australia to launch a recovery mission from Port Moresby.
“We had a pretty good idea of where the glider would be so I decided that it was worth a go to get out there on the water and try to find it,” said Stanley.
Unfortunately Dennis Stanley couldn’t get a good fix on its location so the mission was abandoned. It wasn’t long before signals from the glider were again picked up, showing that it had been transported down towards north Queensland. Feeling more confident of success, he set out again to find the glider, this time from Cooktown. In the early hours of the morning, the runaway glider was located and recovered. Coincidentally, it was found in almost the same location as that of its last dive before it encountered problems.
Craig Steinberg, a researcher from AIMS and an IMOS facility leader, followed the journey of the glider with interest. He noted that the glider followed a similar path to that of the ornate tropical rock lobsters, which walk along the shelf from Torres Strait each August to spawning aggregation locations such as off Yule Island, NW of Port Moresby from November to January. The lobsters' larvae continue to use the same currents of the Gulf of Papua gyre and associated eddies to re-settle on the Great Barrier Reef shelf.
Leader of the IMOS Ocean Gliders facility, Chari Pattiaratchi, commented on the successful recovery of the missing equipment:
“Our back-up plan of attaching tracking devices to the gliders was really worth it. Glider technology is generally very reliable and we rarely have problems but this is the open ocean and there are so many variables out there it pays to be cautious,” he said.
The satellite tracking tags are helping IMOS to reduce the risk of losing equipment such as the autonomous moorings and seagliders in the very remote marine regions in which IMOS operates.