Developed following the devastating effects of the 2004 Indian Ocean Tsunami, the Sonardyne system is based upon a Compatt 5 subsea transponder that uses the latest wideband acoustic signal technology to provide dependable communications through deep water. If the Compatt detects the water pressure changes that indicate a potential tsunami, it will send a warning message acoustically to a surface buoy. A transceiver on the buoy will then relay the message to a control centre onshore via a satellite data link.

Compatt 5s are used extensively in the oil and gas industry, where their reliability and performance is regularly trusted for use on the most complex subsea construction survey projects.

An important advantage of the Sonardyne system is that it functions as a single compact unit. The Compatt 5 can provide reliable communications in water up to 7,000m deep and it contains a high accuracy pressure sensor, battery, transducer, acoustic release and data logger. The compact design eliminates the use of cables and connectors in underwater equipment which can be vulnerable to failure. A floatation collar fitted to the Compatt 5 ensures that it remains tethered upright on the seabed at all times. It also enables it to be recovered for servicing and battery replacement when a coded acoustic signal activates a release mechanism and allows it to float to the surface.

The use of Sonardyne’s new intelligent wideband technology has made it possible for NIOT to increase the efficiency of the through-water communication needed when providing a tsunami warning. It also reduces the Compatt’s power consumption which enables it to remain in continuous monitoring mode on the seabed for up to four years. The buoy mounted surface transceiver will receive hourly reports from the Compatt 5 on the seabed throughout this time.

As soon as the Compatt detects changes in pressure readings it switches into the tsunami warning mode. An alert message is then sent every 15 seconds up to the buoy acoustically, from where an Inmarsat-C satellite terminal relays it to the NIOT Shore Station from where warnings can be issued to vulnerable communities.