Measurements of the acoustic pressure sensitivity of the GeoLab DAS cable off Madeira

Distributed acoustic sensing (DAS) is a novel tool in underwater acoustics that measures strain in an optical fiber from the phase change of backscattered coherent light to estimate acoustic pressure. This technology transforms fiber-optic cables into dense, synchronized arrays of thousands of acoustic sensors, offering unique opportunities for marine research. However, the directivity and frequency response of DAS measurements remain poorly understood. An experiment was conducted in 2025 to characterize the DAS acoustic pressure sensitivity of the GeoLab cable off the southern coast of Madeira Island. Sound source was deployed from R/V Discovery at 14 m depth, with a reference hydrophone suspended 1 m below the source. Data acquisition covered three short towed transects and six stationary stations at 100–3000 m ocean depths. The source repeatedly transmitted a signal comprising chirps in the 105–160 Hz band and 11 tonals between 55–195 Hz. Ambient and DAS self-noise were evaluated during periods between the transmissions. Gaussian beam and wide-angle parabolic equation-based propagation modeling was performed to account for sloping bathymetry and surface reflections. Results of the measurements of the frequency and angular dependence of DAS pressure sensitivity and signal-to-noise ratio will be presented. [Work supported by NSF and NERC.]