Nick Carne
Engineers in the US have built an autonomous underwater vehicle (AUV) that appears to up the ante in terms of underwater skills and endurance.
Clio can move vertically and drift horizontally along the water column while sampling large volumes of seawater to collect microbial and chemical data. And it can do this at depths of up to six kilometres for as many as 14 hours at a time.
Most importantly, the designers say in a paper in the journal Science Robotics, you can then just lift it out of the water and move on, allowing you to gather data and samples that span ocean basins within weeks.
“Clio collects a full suite of samples synoptically during a single dive in a fraction of the time required by current methods,” they write. “Clio also enables autonomous sample collection concurrent with existing wire-based techniques, or other activities, which frees the research vessel and investigators to conduct more research.”
While diving, Clio is subject to Lagrangian horizontal transport dependent on the prevailing vertical currents, as this results in better samples that are more representative of the water mass being studied, the researchers say.
It typically surfaces two to 15 kilometres from the launch site, but in one extreme case at the edge of the Gulf Stream Current appeared 34 kilometres away.
John Breier from the University of Texas Rio Grande Valley and colleagues from institutions in the US and Bermuda designed Clio then tested it on 26 dives over several years.
Using sensors and sampling technologies to collect data, it brought back small- and large-volume samples that enabled genomic and proteomic analysis of biomass at previously unexplored depths, improving upon prior global genomics surveys that had focused almost entirely on the upper water column.
In one survey, it mapped a 1144-kilometre transect of the Sargasso Sea at depths of up to a kilometre. Part of the Atlantic Ocean, this is the only sea in the world without a land boundary, and it thus is defined only by ocean currents.
Traditional sampling can be laborious, the authors say, requiring repeated release and recovery of equipment from vessels, and most AUVs can access the upper 100 metres of the water column, or the area between 3000 and 5000 metres deep, but not both.
Essentially, they suggest, Clio is a “reimagination of AUV design applied to vertical profiling”.
“It builds upon sample return instrumentation and techniques developed for the deep sea, where biomass concentrations are low, and applies them to the full-water column. It is designed and optimised for a single purpose and a mode of science operations orthogonal to previous AUV applications.”
Jnaneshwar Das and Elizabeth Trembath-Reichert from Arizona State University, US, are impressed both with the product and the process. “Development and testing of such systems require a concerted effort between engineers and scientists, and Clio is an excellent demonstration of such synergy,” they write in a commentary in the same journal.
And while they note that there “is, of course, room for improvement with respect to onboard autonomy”, they are also looking ahead.
“It will also be interesting to consider a swarm of Clios coordinating to sample, spatially and temporally, a large section of the ocean. This approach could benefit from optimal control to ride ocean currents to create optimal dispersion from other robots in the team.”