Abstract: A method of measuring temperature comprises the steps of consecutively launching (1, 2) input pulses of light at two different wavelengths into a temperature sensing element in the form of an elongate optical fibre (3); passing Raman scattered light from said element and deriving from said input pulses to intensity detectors (7, 8); obtaining from the detectors (7, 8) output signals indicative of the intensity of the Raman scattered light; and processing said output signals to provide a temperature measurement. A known position (10) along the optical fibre (3) is maintained at a known temperature to provide a reference for deriving temperature measurements at other positions along the optical fibre.

Abstract: Temperature is measured by launching pulses of light into an elongate optical fibre and determining the temperature at positions along the fibre from the intensity of light scattered at those positions. The input pulses can have either the same or two different wavelengths, and the scattered light can be either Raman or Brillouin scattered and either forward scattered or backscattered. One position along the fibre can be maintained at a known temperature in order to provide a reference for other calculations. In particular embodiments the temperature is derived from the ratio between the intensities at two anti-Stokes wavenumber shifts or between an anti-Stokes scattered and a Rayleigh scattered intensity measurement. Otherwise the intensities of Stokes and anti-Stokes shifted Brillouin back scattered light can be used to derive the temperature.