National Physical Laboratory

Underwater sounds detected by optical fibre

NPL worked with Silixa to characterise their Intelligent Distributed Acoustic Sensor (IDAS) - the world's first truly distributed optical fibre acoustic sensor.

The IDAS system is the world’s first truly distributed optical fibre acoustic sensor (image courtesy of Silixa)
The IDAS system is the world's first truly distributed
optical fibre acoustic sensor (image courtesy of Silixa)


The Silixa Intelligent Distributed Acoustic Sensor, or IDAS, works by picking up digital sound signals along an optical fibre cable. By measuring the time taken between launching a laser pulse along the cable and the signal being reflected back, the system detects an acoustic signal at all points along the full length of the cable - for up to 40 km. Essentially, the fibre acts like an acoustic antenna, picking up a signal that is then processed and used for applications such as flow metering, acoustic imaging and perimeter monitoring.

The Challenge

Silixa wanted to characterise the IDAS system using traceable data and NPL, as the UK's National Measurement Institute, can provide traceability to international standards and direct comparisons with known acoustic sources. A Technology Innovation Fund (TIF) project was set up to carry out the work.

The Solution

NPL scientists created a known underwater acoustic sound field using the NPL underwater acoustic reference transducers. The IDAS sensor was then exposed to this field and the output compared with the known input, by cross-referencing the data. As the location of each of the NPL transducers is known, the location data output from the IDAS system can also be tested.

NPL provides a unique range of underwater acoustics facilities and services to meet the individual needs of customers such as Silixa, delivering measurement solutions to help products reach their full potential. These facilities include two open water test tanks that provide flexible approaches to the most demanding testing requirements such as the calibration of hydrophones (underwater microphones) and the characterisation of sonar instruments.

More on NPL's open water testing facility

More on NPL's work on Underwater Acoustics

More on the Technology Innovation Fund

For further information, please contact Justin Ablitt

Last Updated: 5 May 2015
Created: 24 Nov 2011


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