ABSTRACT
This chapter examines the application of distributed acoustic sensing (DAS) in infrastructure, using a single fiber in an optical fiber sensing cable. Usually, the sensor operates using regular monomode optical fiber cables of the same type as those used for telecommunications, but, in some cases, the cable may occasionally be custom designed to withstand severe environments or to improve sensing performance. DAS technology typically employs a modified form of the optical time domain reflectometry (OTDR) principle. Assuming a constant propagation velocity of the probe pulse, the variation of the measured backscatter intensity, as a function of time, can infer information about the waveguide as a function of position. The range over which an OTDR can effectively operate is determined by the fundamental noise in the detection system and the detected signal power, which determine the signal-to-noise ratio. Unlike normal OTDR systems that utilize an incoherent light source, DAS typically uses a coherent illumination pulse, as technique relies on optical interferometry.
