Last updated April 17, 2018 at 11:09 am
You’ve probably heard of the mantis shrimp because of its powerful underwater punch. But there’s more to this little creature than a water-boiling-blow Muhammad Ali would be proud of.
US scientists have developed a new underwater GPS method by using a bio-inspired camera that mimics the complex visual system of the mantis shrimp.
This is the first time that scientists have been able to demonstrate an underwater positioning system which doesn’t rely on satellites but instead exploits the properties of light near the ocean’s surface.
Polarised light for positioning
Light from the sun bends and scatters when it enters the water, polarising light waves in various directions. As humans, we are not able to see this optical phenomenon but a variety of marine animals, including the mantis shrimp, can. This helps them navigate, detect predators and prey, and possibly even communicate with each other.
By using the unique fingerprint created by light’s interaction with water the research team was able to take advantage of something that other biologist simply dismissed as a camera malfunction.
“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 study leader Viktor Gruev, from Carle Illinois College of Medicine.
The researchers found they could 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.
The camera, aptly named MantisCam, is able to detect how light refracts, or bends, when it passes through the surface of water and bounces from particles and water molecules.
“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.
The team discovered that they were able to determine their location with an error of six meters for every 1 kilometre travelled.
“We found that we can locate our position on the planet within an accuracy of 61 km.” says Gruev.
While this falls sort of the accuracy of conventional GPS systems, the technology may open up new ways for people and robots to better navigate underwater using visual cues from polarized light.
“We could use our underwater GPS method to help locate missing aircraft, or even create a detailed map of the seafloor,” said co-author Samuel Powell.
This research could also provide new insights into the migratory behaviour of many marine species.
“Animals like turtles and eels, for example, probably use a slew of sensors to navigate their annual migration routes that take them thousands of miles across oceans,” Gruev said.
“Those sensors may include a combination of magnetic, olfactory and possibly – as our research suggests – visual cues based on polarisation information.”
This insight into the secret polarised world of marine animals could also explain why pollution may cause a problem with navigation.
“It is very likely that increased pollutants in the air and water alter underwater polarisation patterns, causing the undersea environment to appear different from what many animals have learned”, said Gruev.
The study was published in Science Advances.