Glider missions are restricted in duration due to battery life and this presents two major issues. Firstly, the amount of data that can be gathered during any single mission depends on how long the glider can stay in the water, and secondly, operational effort and expense is increased with each recovery and deployment.
In a collaboration with Master Instruments, the team at the IMOS Ocean gliders facility set out to address these two issues. Together, they developed an innovative rechargeable battery pack that is likely to double the amount of data that can be collected by the glider fleet each year without any additional expense.
IMOS Ocean gliders facility Operations Manager, Mr Dennis Stanley, who is based at the Oceans Institute at the University of Western Australia, explained the benefits of the new rechargeable battery packs.
“Firstly, the increased battery capacity means that longer missions involving significantly more data collection days (DCDs) are possible,” said Mr Stanley.
“The old single-use battery packs constrained us to a maximum of about three weeks at sea, and longer missions would have required us to turn some sensors off to conserve power.
“Four weeks at sea with full data collection every day is now very doable so we can observe specific ocean events over longer time periods,” he said.
Powered by one of the new battery packs, Slocum glider U239 set a new IMOS Ocean gliders endurance record of 30 continuous DCDs with relative ease. A recent Two Rocks mission was on track for 34 days but completed its science objectives early so was recovered.
“The second major advantage of using these new batteries is it takes fewer missions to collect the same amount of data and that means less operational time and less expense,” said Mr Stanley.
In addition to the longer missions and less operational effort, the new batteries can be recharged from mains power, without needing access to sophisticated lab facilities. Gliders can now be turned around within 24 hours if required, more or less on-site, even along relatively remote parts of coastline.
Previously it could take weeks or even months to refurbish gliders after a deployment, because replacing the single-use battery would also necessitate re-ballasting, re-calibrating the compass and other instruments as well as overland transport of the gliders to labs across the country, sometimes even internationally. In 2016 Unit 239 completed 2 Bonney Upwelling missions in South Australia, being recovered, charged, driven back to the start and redeployed 48 hours later. After completing the second, record endurance 30 day mission, this unit travelled by truck to NSW and completed two more missions before being returned to the lab for a major service. This saved a remarkable six transits of the continent by truck and weeks of lab time.
Other efficiencies are also becoming apparent. Unexpectedly short missions – such as a recent deployment on the Two Rocks transect that required an emergency recovery on the 9th day because a shark bite destroyed the glider-mounted CTD – would previously have wasted an entire single-use battery with little data to show for it. Using a rechargeable battery pack means data collection can be resumed much more quickly than before, without such wastage.
Having effectively doubled the capacity for the Slocum glider fleet to deliver ocean observations, this successful research-industry collaboration is looking at the possibility of further innovation. Newer Slocum gliders can theoretically take an even larger battery pack so there are plans to take advantage of this to further increase the duration of glider missions.
Second generation batteries, currently being developed, are based on lithium technologies and will stay charged even longer. Innovations include a redesigned battery case to accept multiple sizes of battery and the possibility of external charging capability which will further decrease handling and turn-around time of the glider.
Daniel Rutkowski, a technical designer with Master Instruments, has enjoyed a long and rewarding relationship with the IMOS Ocean gliders facility.
“It’s been a great opportunity for us to be able to work on something so cutting-edge, and to be able to assist an Australian organisation.
“Transporting lithium batteries internationally has its challenges and therefore additional cost, so it makes perfect sense to manufacture these locally,” said Mr Rutkowski.
Greater mission duration, however, does present new challenges. Longer time at sea increases the likelihood of sensor biofouling in some regions. In warmer water biofouling of sensors limits effective mission length to 25–30 days. This is still a work in progress.
Mr Stanley said he is keen to continue working with industry partners to make sure the IMOS Ocean glider fleet is delivering the best possible ocean glider data for Australia.
This article is based on text originally written by Suzanne Long, Turn the Tide Pty Ltd.