We report on the theory and use of pre-amplification to enhance the measurement range of a spontaneous Brillouin intensity based distributed fiber-optic sensor. One factor that limits temperature resolution is receiver sensitivity, which degrades for long range sensors. Using optical preamplification before photodetection in a 23km sensor improved the signal-to-noise by approximately 17dB using a 20MHz detector. The major source of noise was amplified spontaneous emission beat noise.
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