Simultaneous optical fibre distributed strain and temperature
measurements have been obtained, by measuring the spontaneous Brillouin
intensity and frequency shift, using the technique of microwave heterodyne
detection. The enhanced stability from using a single coherent source combined
with optical preamplification results in a highly accurate sensor. Using this
sensor, distributed temperature sensing at 57 km and simultaneous distributed
strain and temperature sensing at 30 km were achieved, the longest reported
sensing lengths to date for these measurements. As a simultaneous strain and
temperature sensor, a strain resolution of 100 µε and
temperature resolution of 4 °C were achieved.
We present a novel technique for performing single-ended distributed fiber temperature measurements by use of microwave heterodyne detection of spontaneous Brillouin scattering. Brillouin frequency-shift measurements were obtained for a sensing length of 57 km, with a spatial resolution of 20 m. The rms error in frequency measurements at the far end of the sensing fiber was less than 3 MHz, and the overall frequency dependence on temperature was 1.07+/-0.06 MHz/K.
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