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Distributed optical fiber sensing based on backward Brillouin scattering has been widely developed during the last decade. Making use of stimulated Brillouin scattering, Brillouin optical time-domain analysis (BOTDA) is considered one of the most performing distributed sensing techniques existing today for long range and quasi-static monitoring of variables like temperature and strain. This has enabled the monitoring of assets over tens of kilometers (even over more than 100 km with advanced configurations and techniques) with typical spatial resolutions of a few meters (typically below 5 m). This paper reviews the fundamentals of BOTDA sensing, its main limitations (essentially imposed by nonlinear effects in the sensing fiber), and advanced methods to enhance the sensing performance. While the performance is ultimately determined by the signal-to-noise ratio (SNR) of the measurements, some of the most relevant methods for SNR enhancement are here reviewed. In particular, and based on recent developments, optimized pulse coding and hybrid optical amplification approaches, specially designed for ultra-long-range BOTDA sensing, are discussed.
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