Pushing the Reach of Fiber Distributed Acoustic Sensing to 125 km Without the Use of Amplification

We report the longest reach fiber based distributed acoustic sensor (DAS) without inline amplification. A measurement range exceeding 112 km, and 125 km if the far end is optimized, is realized with a suitable signal to noise ratio (SNR) for real-world applications. This is achieved by a DAS system optimized for long distance measurements and a combination of different fiber types optimized either for low loss or for high backscatter coefficient.