20 km distributed temperature sensor utilising spontaneous Brillouin scattering

Summary form only given. Brillouin scattering is seen as a potential replacement for the Raman scattering that is already used in commercial distributed temperature sensors. Two parameters of the Brillouin scattering are temperature dependent: the Brillouin frequency shift (which also has a strain dependence) and the intensity of the spontaneously back-scattered Brillouin line. Several systems have been developed for the measurement of the Brillouin shift, but recently attention has focused on the second parameter because, if combined with the first, it should enable the determination of both temperature and strain. Unfortunately, the form of the back-scattered spectrum, composed of Brillouin and Rayleigh lines separated by roughly 10 GHz, makes both interferometric or heterodyne detection schemes hard to implement.