By DIVE Staff
As underwater functionality becomes increasingly prevalent among the latest models of smartphone, a team of engineers from the University of Washington has developed the first underwater 3D-positioning app for smart devices, using the devices’ speakers and microphones to communicate using acoustic signals beneath the surface.
Underwater positioning technology has been something of a holy grail in the scuba diving world. Above the surface, GPS relies on a vast network of satellites which communicate with smart devices via radio waves, but the high-frequency signals necessary for communication are unable to penetrate water to any great depth.
Acoustic signals, however – sound waves – are capable of propagating great distances through water, although using sound waves to transmit data presents a separate challenge due to the slower speed of sound and the difficulties of maintaining a coherent data stream through the water.
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Current incarnations of underwater location tracking involve the use of surface buoys through which all communications are relayed, but these are expensive and cumbersome to deploy, and hence are not in widespread use.
A dive computer using ultrasonic buddy-to-buddy-communications was launched in 2019, although the Swedish-made Oceans S1 Supersonic is limited to push-button notifications which will alert divers in a group with a haptic ‘ping’, and – at the time of writing – is currently unavailable.
The University of Washington team’s app links smart devices together without the use of a buoy, however, instead using the devices’ speakers and microphones to communicate with each other, allowing divers to be tracked by the app as long as they remain within approximately 30m (98ft) of each other.
Distance is estimated using send-and-receive timestamps, allowing the app to plot the dive team’s formation and each diver’s location within it. If the divers are using smart computers such as the Apple Watch Ultra and Garmin Descent series of computers, the app can locate the divers in 3D.
‘Mobile devices today can work nearly anywhere on Earth. You can be in a forest or on a plane and still get internet connectivity,’ said lead developer Tuochao Chen, a UW doctoral student in the Paul G Allen School of Computer Science & Engineering. ‘But the one place where we still hadn’t made mobile devices work was underwater. It’s kind of the final frontier.’
The app needs at least three devices in its network to function, and its accuracy improves as more devices are added. When tested with four to five devices in local lakes and a pool, the app estimated locations with an average error of about 1.6m (5ft) — close enough for divers to see each other in most environments.
Accurate GPS positioning information could be added to the app if the lead diver were to be wirelessly connected to a GPS locator device based on a boat or buoy.
The study builds on a previous breakthrough from the lab called AquaApp, which allows divers to send messages to each other underwater.
‘This and AquaApp can be used together,’ said author Justin Chan, a UW doctoral student in the Allen School. ‘For example, if the dive leader finds someone going the wrong way, the leader can send an alert: “Hey, you’re going out of range. You need to come back.”
‘Or, if a diver is running out of oxygen, an SOS can let the team find the person quickly, even in murky water.’
The team will present its findings at the Special Interest Group on Data Communication (SIGCOMM) 2023 conference in New York City, to be held this year between 10-14 September.
More information about the app can be found on the team’s website, including the publication of its open-source code.
