Measurement of ocean currents by seafloor distributed optical-fiber acoustic sensing.

This article focuses on the use of distributed acoustic sensing (DAS) technology applied to a pre-existing seafloor optical-fiber (OF) cable for in situ monitoring of ocean surface gravity waves (OSGWs) and ocean currents. By analyzing OSGW-induced microseismic noise through ambient-noise interferometry and frequency-domain beamforming, the study successfully inverted water depth and time-averaged current velocity along a 33.6 km cable segment in the Zhoushan Archipelago, China. Hourly variations in current velocity were further retrieved using a frequency-domain waveform-stretching method and validated against nearby ocean buoy observations and forecasting data, showing general phase agreement despite some magnitude discrepancies. The findings demonstrate the potential of DAS-instrumented OF cables as effective, high-resolution tools for monitoring shallow-water ocean currents.