Engineers in the UK have developed a way to simultaneously monitor every point along an underwater pipeline using fibre-optic cable.
Hertfordshire-based sensor firm Silixa said the technology is the world’s first distributed optical-fibre acoustic sensor, meaning it can detect sound at every point along a cable.
The Intelligent Distributed Acoustic Sensor (IDAS) replaces the use of large numbers of underwater microphones or hydrophones, meaning it could be used in military underwater listening, seismic surveys and measuring sound from underwater construction.
‘Acoustic signals consist of tiny pressure fluctuations,’ Daniel Finfer, Silixa’s acoustic development manager, told The Engineer. ‘In the presence of an optical fibre, these pressure fluctuations change the way light is transmitted.
‘By monitoring the change in backscatter [a type of reflection] precisely and rapidly, one can observe the acoustic field at every point along the length of a fibre.’
The backscattering occurs naturally as light travels down an optical fibre. ‘By recording the returned signal against time, a measurement of the light scattered at each point along the fibre can be determined,’ said Finfer.
The technology enables engineers to continuously monitor the volume and rate of fluid travelling through an underwater pipeline, as well as detecting bubbles, blockages and leaks.
IDAS was tested with the help of the National Physical Laboratory (NPL), which provided a way of matching sound and light patterns in the controlled environment of an underwater acoustic test facility.
‘The role of NPL in this development was to create a known and characterised acoustic environment,’ said Justin Ablitt from NPL’s Centre for Mechanical and Acoustical Metrology.
‘We can then expose the system under test to acoustic pressure. Silixa can then analyse the data and relate that back to exactly what the system was exposed to. So that way you can see how it’s behaving in a traceable chain.’