Is this the new wave of submerged communications?
By: Kelsey Atherton August 29, 2018 C4ISRNET
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The ocean hides what
it contains, and it is in that hiding that submarines have their power. Lurking
under seas, at first with just enough capability for an attack run and now with
the ability to lurk for months at a time, submarines remain power out of reach,
unseen until engaged in combat or resupplying in a friendly port. That stealth
comes at a cost, however, besides the simple perils of existing underwater.
When submerged,
submarines are more or less on their own until they resurface again, since
radio waves do not travel well through seawater. Or they are for now. New
research by MIT, presented at a conference in late August, devised a way for
submerged submarines to communicate wirelessly with people on the surface by
combining hydroacoustics and acoustic radars.
Presently, submarines
communicate either across normal radio frequencies when surfaced or through
hydroacoustic signals and listening posts underwater that can transmit the
messages back to counterparts on shore. Very and extremely low-frequency radio
waves can be transmitted in a way that submarines can listen to below the
surface, but it’s a one-way form of communication, from stations on land to
submarines. To get something responsive, with the flexibility to communicate
away from static seabed hydrophones, needs something else.
Specifically, it
needs a way to combine hydroacoustic transmission from the submarine through
water that can then be converted into a useful data.
“We present a new
communication technology, translational acoustic-RF communication (TARF),”
write paper authors Francesco Tonolini and Fadel Adib of the MIT Media Lab.
“TARF enables
underwater nodes to directly communicate with airborne nodes by transmitting
standard acoustic signals. TARF exploits the fact that underwater acoustic
signals travel as pressure waves, and that these waves cause displacements of
the water surface when they impinge on the water-air boundary. To decode the
transmitted signals, TARF leverages an airborne radar which measures and
decodes these surface displacements.”
In testing, they
demonstrated that the communication technique can transfer data at standard
underwater bitrates up to 400bps, and even do so with surface waves 6.3 inches
crest-to-crest, or 100,000 times larger than the surface perturbations made by
the acoustic transmitter.
Right now, this
communication is one-way. While the signal transmitted up from the water
produces useful information at the boundary with the air, a signal transmitted
through the air downwards would disintegrate on integration with water. This
one-way is distinct from previous forms of communication with submarines,
however, as it lets the submarine talk without revealing its position to
surface sensors.
Despite the
limitations, and the earlierness of the research, Tonolini and Adlib see a
bright future for the technology, as a way to enable a host of new technology
in machines. The technology, they write, can enable “many applications
including submarine-to-drone communication, deep-sea exploration, and subsea
IoT (Internet of Things).
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