A phase-based approach to speed of sound estimation in DAS

This study presents an approach for estimating the Speed of Sound (SoS) in fluids flowing through pipes equipped with Distributed Acoustic Sensing (DAS) arrays. The method integrates phase-based coherence analysis, robust time windowing, and targeted filtering in both frequency and spatial domains to reduce the impact of noise on solution confidence. Collective phase correlations are calculated across selected DAS signal pairs, with key frequency bands isolated to enhance measurement accuracy. Results are displayed as likelihood plots for both positive and negative SoS over various ranges, providing insights into fluid type, flow velocity, and flow regime within the pipe. Our findings demonstrate a promising reduction in SoS measurement uncertainty compared to both 2-D FFT FK and cross-correlation approaches over an equivalent spatial aperture, highlighting the method’s potential for more accurate flow characterization in DAS-equipped systems.