Human vision is poorly equipped to pick out details beneath the surface of the ocean – mainly because our species descends from a lineage that has existed stubbornly on dry land for millions of years.
Shrimps, on the other hand, come from a long line of, well, shrimps, and have evolved exquisitely sensitive underwater vision based on polarisation.
Now, an international team of researchers, including scientists from Australia’s Queensland Brain Institute (QBI), have taken a lesson from the crustaceans and develop a radical new type of underwater geo-localisation system.
The system uses polarisation – the bending, refracting and scattering of light as it passes through water – to calculate the position of objects. A proof-of-concept study published in the journal Science Advances carries the promise of dramatically increased accuracy in navigation, exploration and deep-sea search-and-rescue missions.
“Most modern navigation techniques don’t work underwater,” says QBI’s Samuel Powell. “Satellite-based GPS, for example, only works to a depth of about 20 centimetres.
“Underwater, visibility is also limited, so relatively old technology such as lighthouses don’t work, because the farthest distance you can see is around 100 metres.”
The accuracy of the shrimp-inspired system grows from a discovery made by Powell and lead author, Viktor Gruev from the University of Illinois at Urbana-Champaign in the US. Using polarisation data gathered from around the world, they realised that the light patterns, far from being random or an expression of the tech used to record them, precisely correlated with the sun’s position relative to the data collection location.
This implied that underwater polarisation data could be used to deduce the sun’s heading and angle of elevation. Combined with the date and time of data collection, it was thus possible to estimate the GPS coordinates of the recording device.
From there it was a comparatively short step to showing that polarisation could be used to determine object location.
“We tested our underwater GPS method by pairing our bio-inspired camera with an electronic compass and tilt sensor to measure the underwater polarisation data at a variety of sites around the globe, depths, wind conditions and times of day,” explains Gruev.
“We found that we can locate our position on the planet within an accuracy of 61 km.”
The researchers say that their system lends itself to being scaled up, to enable large-scale exercises such as seafloor mapping at a fraction of the cost of presently available methods.