Strain monitoring using distributed Rayleigh sensing

Rayleigh Backscatter has been used for many years as the source signal for fibre optic distributed acoustic sensing (DAS) in many industrial and civilian activities such as situational information monitoring and down-hole hydrocarbon exploitation. The signal from a DRS system is affected by temperature, strain and acoustics/vibrations. The very low frequency content representing temperature and strain contributions has historically been overlooked in favour of the higher frequency acoustic content. In this paper we describe the potential of a quantitative DRS system to deliver low frequency strain monitoring together with an understanding of the degree of thermal coupling to the system which allows useful results. A long term (50 day) measurement using a quantitative DRS system was carried out to investigate how much drift there was in the system and demonstrate a compensation approach. An example of strain monitoring in a novel pipeline system is illustrated to show the degree of measurement resolution deliverable as compared to conventional strain gauges.