Patent attributes
A method of obtaining a distributed measurement comprises deploying an optical fibre in a measurement region of interest, and launching into it a first optical signal at a first wavelength λ0 and a high power level, a second optical signal at a second wavelength λ−1, and a third optical signal at the first wavelength λ0 and a low power level. These optical signals generate backscattered light at the second wavelength λ−1 arising from Raman scattering of the first optical signal which is indicative of a parameter to be measured, at the first wavelength λ0 arising from Rayleigh scattering of the first optical signal, at the second wavelength λ—1 arising from Rayleigh scattering of the second optical signal, and at the first wavelength λ0 arising from Rayleigh scattering of the third optical signal. The backscattered light is detected to generate four output signals, and a final output signal is derived by normalising the Raman scattering signal to a function derived from the three Rayleigh scattering signals, which removes the effects of wavelength-dependent and nonlinear loss.
