Dual-Domain SNR Enhancement and Fading Suppression Method for ϕ-OTDR

Phase fading and noise are critical issues that hinder phase recovery and location in phase-sensitive optical time-domain reflectometry (ϕ-OTDR) based on distributed acoustic sensing (DAS) systems. This paper introduces a novel approach for signal-to-noise ratio (SNR) enhancement and fading suppression by proposing a Dual-Domain SNR Enhancer (DDSE) method. This method simultaneously processes Rayleigh backscattered (RBS) signals in both the digital and image domains, achieving fading suppression and further noise reduction. In the digital domain, it rotates the complex vector signal and suppresses fading through the moving average in each signal trace. In the image domain, we design and optimize a Discrete Cosine Transform Non-local mean (DCT-NLM) image processing algorithm based on the characteristics of OTDR signals, achieving distortion-free signal recovery and noise reduction. We verify the principle and mechanism of this method both theoretically and experimentally on a ϕ-OTDR system with a 6 km optical fiber. The DDSE method achieved a 26.68 dB reduction in phase noise level and a 14.8 dB enhancement in signal recovery SNR. The method effectively achieves noise reduction and signal enhancement through experimental validation, demonstrating its practicality, reliability, and potential to enhance the performance of ϕ-OTDR systems.