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radio, television, cordless phones, Wi-Fi and Bluetooth.

Extremely low frequency (ELF) sys- tems were used for submarine communi-

Subsea cations during the Cold War. Operating at 76-82Hz, they sent a few characters per minute across the globe, acting as signal to another submarine to surface for higher-bandwith communications using terrestrial radio.

To create a radio signal, electrical energy is changed into electromagnetic energy. The transmitter provides electri- cal current at an appropriate frequency.

The signal is then modulated, to carry data, and launched via an antenna.

A receiver antenna detects the signal,

A subsea ? eld, with NASNet positioning which is then demodulated at the remote stations to provide acoustic positioning. receiver.

Image from Nautronix.

Radio signals are attenuated when

Nautronix, based in Aberdeen. “Early (BOPs) or isolation devices. Here, it has propagating through conductive media. implementations of acoustic communica- predominantly been a secondary system, Seawater is particularly conductive. tions and positioning systems were seen backing-up a primary wired system. But, Attenuation increases with frequency as being unreliable and susceptible to some are starting to use it as a primary in the radio spectrum, therefore subsea interference. system (see case study). radio systems use low frequency radio. “Going back 30 years or so, acoustic New acoustic systems are also merging

At very short distances (

HD video), using a higher frequency, of signaling was relatively straightforward this is Nautronix’s NASNet system, which enabling great data to be modulated into to generate with the available hardware of provides ? eld-wide life-of-? eld position- the radio waves. RF signals are immune to acoustic the time, but it was susceptible to interfer- ing and communications.

ence. Since then, the underlying signaling noise interference, and any negative

In 2008, Murphy Oil deployed an acous- has developed dramatically and signal effects of turbidly and bio-fouling. tic control system for a surface BOP integrity has increased substantially, lead-

Subsea RF also doesn’t suffer interfer- application in 1200m water depth, on ing to an overall increase in the robustness ence subsea from other radio, i.e. radio the Azurite FPSO o