Distributed fiber optic strain and temperature sensing for structural health monitoring

Distributed fiber optic sensing presents unique features that have no match in conventional sensing techniques. The ability to measure temperatures and strain at thousands of points along a single fiber is particularly interesting for the monitoring of large structures such as bridges, pipelines, flow lines, oil wells, dams and dikes. Sensing systems based on Brillouin and Raman scattering have been used for example to measure cables and pavement temperatures in bridges, detect pipeline leakages, prevent failure of pipelines installed in landslide areas, optimize oil production from wells and detect hot-spots in high-power cables. The measurement instruments have been vastly improved in terms of spatial, temperature and strain resolution, distance range, measurement time, data processing and system cost. Analyzers for Brillouin and Raman scattering are now commercially available and offer reliable operation in field conditions. New application opportunities have however demonstrated that the design and production of sensing cables is a critical element for the success of any distributed sensing instrumentation project. Although standard telecommunication cables can be effectively used for sensing ordinary temperatures, monitoring high and low temperatures or distributed strain present unique challenges that require specific cable designs. This contribution presents different cable designs for high-temperature sensing, strain sensing and combined strain and temperature monitoring, as well as relevant application examples to the monitoring of civil and oil & gas structures.