The mantis shrimp’s ability to see circular polarized light inspires an underwater GPS system.
Shrimp-inspired navigation. I’m Bob Hirshon and this is Science Update.
GPS systems have revolutionized navigation across the globe. But GPS radio signals don’t travel underwater, hindering geolocation. Enter the mantis shrimp, a creature whose eyes act like sophisticated polarized sunglasses, able to detect patterns of light that bend as they pass through water. University of Illinois Urbana-Champaign engineer Victor Gruev says that these polarization patterns change depending on the position of the sun, a feature which could be used for navigation.
All these polarization signatures underwater, they are dependent on the sun’s location with respect to where you are.
In the journal Science Advances, Gruev’s team describes a shrimp-inspired underwater GPS system. The technology could aid exploration, pollution tracking, and animal migration research. I’m Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
Since the time that people took to the seas to explore the world, they have been searching for reliable ways to help them navigate. The early Pacific Polynesians, for example, were the first to use the motion of the stars, weather, the position of certan wildlife species, or the size of waves to help them navigate from one island to another. The Vikings, like Floki Vilgerdarson who is credited with discovering Iceland, would use ravens to help navigate. The Vikings would release a raven if they thought land was near. If the raven kept circling the ship without purpose, then it was thought they weren't near land. If, however, the raven took off in a certain direction, the Vikings would follow it thinking it was headed toward land.
The first useful invention to help was the magnetic compass. Sailors still had to use a compass in combination with their knowledge of how fast they were travelling, their current lattitude, and an accurate clock in order to figure out their longitude. Another early useful instrument for navigation was the sextant—and it's something that is still in use today. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation.
These days, all large ships rely on global positioning systems (GPS). A marine GPS provides longitude and latitude. Many GPS can also show the approximate depth of the water. Under the water, however, a traditional GPS is not reliable because it requires line-of-sight to satellites, and water interferes with that process. Hence, the need for the underwater GPS method developed by Victor Gruev and his team. This new technology is called the Mantis Cam—an ultra-sensitive camera capable of sensing both color and polarization—and was developed by mimicking the eye of the mantis shrimp. In other words, it was bioinspired (inspired by or based on the biological structure) by the eye of the mantis shrimp.
The mantis shrimp, considered one of the best hunters in shallow waters, possesses one of the most sophisticated eyes in nature. Compared with human vision, which has three different types of color receptors, the mantis shrimp has 16 different types of color receptors and six polarization channels (the polarization of light is the direction of movement of light as it vibrates in space). That is, the camera can show the underwater environment as a vast landscape of polarization patterns, instead of a dull-blue, featureless space that we see with our human eyes.
Using this new camera, Gruev and his team developed an underwater GPS method by using polarization information collected with it. The camera takes advantage of how light refracts, or bends, when it passes through the surface of water and bounces from particles and water molecules. They collected underwater polarization data from all over the world in their work with marine biologists and noticed that the polarization patterns of the water were constantly changing. Once back at the lab, the team determined that the underwater polarization patterns are a result of the sun’s position relative to the location where the recordings were collected. They found they can use the underwater polarization 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.
According to Gruev, “We found that we can locate our position on the planet within an accuracy of 61 kilometers (38 miles).” That might seem like a huge error range, but it’s still fairly remarkable considering the size of the Earth’s oceans, which each cover tens of millions of square kilometers.
The researchers are hopeful that the new technology can be used to help find the remains of sunken ships, locate missing aircrafts, or create detailed maps of the ocean floor. They think the research could also lead to new insights into the migratory behavior of many marine species.
Now try and answer these questions:
- How did people first try to navigate on a ship?
- What does GPS stand for? Why can't it be used effectively underwater?
- What is the Mantis Cam? What was it inspired by?
- What makes the Mantis Cam different from other cameras?
- How did Gruev and his team use the Mantis Cam to help determine their location underwater?
- Can you think of other technologies that have been inspired by animals?
If you want to learn more about other technology inspired by animals, check out the Robo Roaches Science Update.
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