Distributed Temperature Sensing 3
Distributed Temperature Sensing 3 : Measuring Principle Raman effect: The light scattered back from the fibre optic therefore contains three different spectral shares: (a) the Rayleigh scattering with the wavelength of the laser source used, (b) the Stokes line components from photons shifted to longer wavelength (lower frequency), and (c) the anti-Stokes line components with photons shifted to shorter wavelength (higher frequency) than the Rayleigh scattering. The intensity of the so-called anti-Stokes band is temperature-dependent, while the so-called Stokes band is practically independent of temperature. The local temperature of the optical fibre is derived from the ratio of the anti-Stokes and Stokes light intensities
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