Don’t you hate it when after you’ve gone only five or ten meters underwater, you completely lose signal? Now, this annoying limitation of modern technology is being addressed by researchers at the University of Washington, who have created an underwater communication app that uses sound signals to relay messages to your other submerged friends. It may sound silly, but millions of people could use this technology in both recreational and professional diving situations.
The problem with underwater communication is simple: radio waves are absorbed by water, and no signal our phones send or receive can travel more than a few inches without being completely lost. That’s one reason submarines and the like need communication: to transmit data back and forth to the surface.
Sound waves, on the other hand, travel through water quite easily and are used by countless aquatic species to communicate. But not humans – because the way we make sound only works well in air. So, since time immemorial, divers have communicated with each other using hand signals and other gestures.
Professional divers will have a vocabulary of dozens of signals, from “low air” to “danger to the right” and anything else you can imagine that comes up during a dive. But you have to learn them and see them in use to work; You can bet that at least some divers wish they could punch out a message like they do above the waves.
This is the idea behind AquaAppa software experiment from the Mobile Intelligence Lab at the UW, led by doctoral student Tuochao Chen and prolific professor Shyam Gollakota.
The system uses a modified form of “chirping,” or using the phone’s speaker to create high-frequency audio signals to transmit data rather than radio. This has been done beforebut not (to my knowledge) in such a simple, self-correcting way that any smartphone can use.
“With AquaApp, we demonstrate underwater messaging using the speaker and microphone widely available on smartphones and watches. Aside from 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 news release.
It’s not as simple as just converting signal to acoustic. Transmission and reception conditions are constantly changing when two people’s locations, relative speeds, and surroundings are constantly changing.
“For example, fluctuations in signal strength are exacerbated by surface, floor and shoreline reflections,” said Chen’s co-author and fellow student, Justin Chan. “Motion caused by nearby people, waves and 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 constantly recalibrates with a kind of handshake signal that phones can easily hear and then report the characteristics. So if the sender’s tone is received but the volume is low and the high end is muted, the receiver sends this information and the sender can modify its transmit signal to use a narrower bandwidth, more power, etc. .
In their field experiments in lakes and a “surge bay” (probably the Shilshole), they found they could reliably exchange data over 100 meters – certainly at very low bitrates, but more than enough to include a set of pre programmed signals corresponding to the old hand gestures. While some (myself included) may lament the loss of an elegant and very human solution to a long-standing problem, the simple truth is that it could make dangerous diving much safer, or allow recreational divers to communicate more than “help” and directions.
However, diving is a pastime and profession steeped in history and tradition, and it’s highly unlikely that this digital communication method will replace gestures – a self-powered analogue alternative is exactly what you want ready as a back-up should things go awry .
The AquaApp code is open source and free to use — take a look and try it yourself in this GitHub repository.