Shedding new light
Lost at sea? This camera mimics ways shrimp see and might help rescuers find you.
LEAVE it to the multi-talented mantis shrimp to unlock the secret to underwater GPS. Two years ago, a University of Illinois researcher, inspired by the slashing, dashing underwater warrior, mimicked its bulging eyes to create a camera able to record polarised light and better detect some cancers. Now he’s used that same technology to develop a method of underwater global positioning.
If it works, cracking the underwater GPS puzzle could have widespread implications, from hastening rescue efforts to improving ocean research.
“We’re collecting vast amounts of data with cameras above water. We’re getting everything from information about the environment to our personal lives,” said electrical engineer Viktor Gruev, who co-authored a study in the journal Science Advances with Washington University engineer Samuel Powell. “So think about putting that under water.”
Global navigation systems rely on an array of satellites circling the earth to provide locations. But those radio signals can’t penetrate water, leaving underwater navigation to bulky, expensive systems based on ultrasound or gravitational fields. The Department of Defense is now in the midst of a years-long effort to develop a network of drones to provide the Navy with its first global positioning system.
Gruev’s camera, which he describes as a “GoPro equivalent”, can’t operate without light, but it does provide a cheaper, more mobile solution than what’s currently available.
The system works by looking at polarised light in water. Based on the angle and time of day, the camera can determine location to within about 59km. Gruev says the team is still working on perfecting the system and shrinking that margin.
In developing the camera, Gruev and Powell also corrected a long held misunderstanding about the properties of polarised light in water.
In the 1970s, Gruev said renowned Yale scholar Talbot Waterman discovered that when light is polarised in water, it doesn’t travel on a uniform horizontal plane as it does above water. Waterman suggested that more research needed to be done, Gruev said, but for the next several decades scientists continued to assume that light moved horizontally. But as they took their camera around the world filming underwater, Gruev and Powell noticed angles were in fact not uniform and changed constantly. Other researchers concluded the camera might have a problem.
“But I was pretty sure my camera was doing its job,” Gruev said.
Instead he theorised patterns were connected to the sun’s location and could in fact be combined with time to determine locations.
“I asked the question, ‘How is light polarised underwater?’” he said, and could the physical principles of water make light polarise differently?
It took a complicated set of models and measurements, and advances in compact camera technology, to prove his point under water.
While it’s too early to say how marine biologists might use the technology, Gruev has some ideas. Like the mantis shrimp, many marine animals use polarised light to navigate. But what if water pollution is changing those polarisation patterns and, for example, causing more whales to beach themselves?
“Animals are winding up in strange places,” he said. “It’s a hypothesis, but it’s a plausible explanation.”
Swarms of robotic cameras could also be used to more quickly locate missing ships and planes, map the ocean floor or track changes on troubled reefs, which in recent years have declined dramatically with rising ocean temperatures. Or roving cameras could wander the oceans, continuously sensing and reporting changes.
“They have to be self-sustaining and relatively low-powered and when they see something be able to communicate it back,” Gruev said. “But all the pieces are there and it will give us a means of better understanding the ocean and where changes are happening.” — Miami Herald/Tribune News Service