Don’t you hate it when, after going just 5 or 10 meters underwater, you completely lose the signal? Now, this vexing limitation of modern technology is being tackled by researchers at the University of Washington, who have created an underwater communication app that uses sound cues to deliver messages to your other submerged friends. It may sound silly, but millions of people could use this technology in recreational and professional diving situations.
The underwater communication problem is simple: R radio waves are absorbed by water, and no signal our phones send or receive can travel more than a few centimeters without being completely lost. That’s one of the reasons submersibles and the like need a tether: to transmit data back and forth on the surface.
Sound waves, on the other hand, travel quite easily through water and are used by countless aquatic species to communicate. Not humans, though – because the way we produce sound only works well in the air. So, for as long as anyone can remember, divers have communicated with each other using hand signals and other gestures.
Professional divers will have a vocabulary of dozens of signals, ranging from “low in the air” to “danger to your right” and anything else you can imagine occurring on a dive. But you have to learn them and see them in use for them to work; you can bet that at least some divers wish they could spread a message like they do above the waves.
That’s the idea behind AquaApp, a software experiment from UW’s Mobile Intelligence Lab, led by PhD student Tuochao Chen and prolific Professor Shyam Gollakota.
The system uses a modified form of “chirping”, or uses the phone’s speaker to create high-frequency audio signals to communicate data rather than radio. It’s been done before, but not (to my knowledge) in such a simple, self-correcting way that any smartphone can use.
“With AquaApp, we’re demonstrating underwater messaging using the speaker and microphone widely available on smartphones and watches. Other than downloading an app to their phone, the only thing people will need is a waterproof phone case rated for the depth of their dive,” Chen said in a UW press release.
It’s not as simple as just converting a signal to an acoustic signal. The transmission and reception conditions are constantly changing when the locations, relative speeds, and environment of two people are constantly changing.
“For example, fluctuations in signal strength are compounded due to surface, ground, and shoreline reflections,” said Justin Chan, Chen’s co-lead author and graduate student. “Motion caused by humans, waves and nearby objects can interfere with data transmission. We had to adapt in real time to these and other factors to ensure AquaApp would work in real-world conditions.
The app is constantly recalibrating itself with some kind of handshake signal that phones can easily hear and then report the characteristics. So if the sender tone is received but the volume is low and the high end is attenuated, the receiver sends this information and the sender can modify their transmit signal to use a narrower frequency band, more power, etc.
In their on-site experiments in lakes and “a bay with strong waves” (probably Shilshole), they found that they could reliably exchange data over 100 meters – at very low rates, of course, but more enough to include a set of pre-programmed signals corresponding to the old hand gestures. While some (including myself) may lament the loss of an elegant and very humane solution to a long-standing problem, the simple truth is that it could make dangerous diving work much safer, or allow divers recreational to communicate more than “help” and instructions.
That said, diving is a hobby and profession steeped in history and tradition, and this digital method of communication is highly unlikely to supplant gestures – an analog, self-contained alternative is exactly the sort of thing you want ready as a backup if things go sideways.
AquaApp’s code is open source and free to use – take a look and try it yourself on this GitHub repository.