Terrestrial Wi-Fi to Boost Underwater Communications

“It’s a just a trade-off between cost, weight, and durability, including rust and corrosion.”

After successful tests in Long Island Sound – an environment that has a lot of reflective acoustic energy – a number of oceanographic researchers started using AquaSeNT’s equipment; the National Oceanic and Atmospheric Administration started using the technology in the Chesapeake Bay. In oceanography applications, various sensors typically collect data on the seafloor or in the water column. Sometimes, a data logger is used to collect and store information over a long period of time, and then retrieved and the data downloaded. Other times, a buoy is placed on the surface, and a cable is run to the seafloor to bring the data to the surface. 

However, in the case of data loggers, at times the equipment fails, and the experiment is lost. And surface buoys create potential problems regarding ship navigation or vandalism, and also suffer from cable failures due to storms and general fatigue. So oceanographers often turn to wireless communication solutions, and are particularly interested in the improved robustness of the OFDM data link.

How Acoustic Underwater Communication Systems Work

The first speed of sound water measurements were conducted in the 1820s, and submarine signaling devices based on acoustics were used around World War I. The earliest acoustic modems first came into use in the 1960s and 1970s, which allowed for data transmission from sensors on a seabed to a surface modem.

These early acoustic systems can be thought of as walkie talkies, in which a message is sent to the sensor package to wake up and send data, and then data is gathered without retrieving equipment from the seabed, Hanson said.

In acoustic transducer systems, a disc or sphere-shaped piezo ceramic crystal transducer is placed in the water and excited with an electrical signal, which causes it to expand and contract with the applied signal. The expansion and contraction converts the electronic signal into a pressure wave, which ripples throughout the water at the speed of sound like a pebble’s ripple on the water’s surface.

The pressure waves eventually reach the receiver, causing it to vibrate and for the original electrical signal to be re-created. Because these pressure waves have been modulated with digital information, they carry the digital information on them to the receiver, and the receiver performs the reverse process, demodulation, and recovers the digital data from the carrier wave.


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