Comparisons of Seafloor Distributed Fiber-Optic Sensing Datasets and Empirical Calibrations for Inferring Ocean Surface Gravity Waves

Abstract Distributed acoustic sensing (DAS) is an emerging oceanographic technique in which an interrogator continuously records nanoscale strain of a fiber-optic cable, such as a telecommunication cable, with meter-scale measurement spacing over tens of kilometers. Empirical methods have recently been established for calculating pressure spectra to measure ocean surface gravity wave statistics from DAS strain. Here, we compile data from six submarine DAS experiments to provide a comparison between studies and establish recommendations for using DAS to measure ocean waves. Data were collected from Alaska, Hawaii, Massachusetts, North Carolina, and Oregon, United States, with different interrogators on different cable types in 0–60 m of water with 0–4 m of burial. Ground-truth measurements of ocean waves were provided by standard near-bed or sea surface instruments. The raw strain recorded in each experiment varied over four orders of magnitude, which could not be explained by water depth, wave conditions, or interrogator settings and suggests that cable characteristics and burial depth are important factors controlling strain magnitude and measurement quality. Strain spectra were converted to near-bed pressure spectra using a frequency-dependent, location-specific empirical correction factor, and DAS-derived pressure spectra were used to calculate wave statistics. The correction factors varied over 10 orders of magnitude between sites yet provided accurate calculations of wave height and period (root-mean-square error of 0.2–0.6 m for H s and 0.2–1.6 s for T e and T p ). The volume of data necessary for calibration is discussed. This meta-analysis highlights future oceanographic applications of DAS. Significance Statement Distributed acoustic sensing (DAS) is an emerging technology for measuring ocean waves on seafloor fiber-optic cables, such as telecom cables. The advantage of DAS is that it can record thousands of measurements per second at meter-scale spacing over tens of kilometers. We compare six datasets to characterize DAS-derived strain for measuring ocean waves. The differences in strain magnitude observed between datasets were not explained by water depth, wave height or period, or instrument settings. It is likely that cable composition and depth of burial control the magnitude of the recorded strain. Despite these differences, each dataset was empirically calibrated to produce accurate measurements of wave statistics. DAS is a promising new oceanographic technology, and new applications should be explored.