GPS Gets Wet

Although scuba and snorkeling enthusiasts dive with smartwatches that can go to depths of over 100 feet, accurately locating mobile devices underwater is a real challenge. Researchers at the University of Washington have developed the first underwater 3D-positioning app for smart devices. If three or more divers are within about 98 feet (30 meters) of each other, their devices’ speakers and microphones contact each other, and an app tracks each user’s location relative to the leader.

Above water, GPS relies on a vast satellite network to locate mobile devices with radio signals. Underwater, the signals fade. Sound, however, travels faster and farther in water. Previous underwater positioning relied on strategically placed buoys, but these systems are expensive and cumbersome to deploy.

Using the app, if the dive leader has at least one other diver visible, the group’s devices send acoustic signals to each other through their microphones and speakers and use the timestamps to estimate each diver’s distance. The app can calculate the group’s formation and each diver’s location. The system can locate divers in 3D if a device also tracks depth.

When tested with four to five devices in local lakes and a pool, the app estimated locations with an average error of about 5 feet—close enough for divers to see each other in most environments. The leader needs to be wirelessly connected to a surface device on a boat with GPS capabilities to get actual GPS coordinates.

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