Scientists have developed a bio-inspired camera that mimics the eyes of a mantis shrimp, an advance that may open up new ways for people and robots to better navigate underwater.
The findings, published in the journal Science Advances, are the first to demonstrate passive underwater global positioning (GPS) using the polarisation properties of underwater light.
The technology developed by researchers at the University of Illinois in the US could open new possibilities for undersea navigation and understanding of the migratory behaviour of marine animals.
The camera, a variation of a polarisation imager named Mantis Cam after the shrimp that inspired it, takes advantage of how light refracts, or bends, when it passes through the surface of water and bounces from particles and water molecules.
"We collected underwater polarisation data from all over the world in our work with marine biologists and noticed that the polarisation patterns of the water were constantly changing," said Viktor Gruev, a professor at the University of Illinois.
"This was in stark contrast to what biologists thought about underwater polarisation information," said Gruev.
"They thought the patterns were a result of a camera malfunction, but we were pretty sure of our technology, so I knew this phenomenon warranted further investigation," he said.
Gruev and graduate student Samuel Powell determined that the underwater polarisation patterns are a result of the sun's position relative to the location where the recordings were collected.
They found that they can use the underwater polarisation patterns to estimate the sun's heading and elevation angle, allowing them to figure out their GPS coordinates by knowing the date and time of the filming.
"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," said Gruev.
"We found that we can locate our position on the planet within an accuracy of 61 km," he said.
This technology may open up new ways for people and robots to better navigate underwater using visual cues from polarised light.
"We could use our underwater GPS method to help locate missing aircraft, or even create a detailed map of the seafloor," Powell said.
"Robots swarms equipped with our sensors could provide a low-cost means of underwater remote sensing - it would certainly be more cost-effective than current methods," he said.
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