Wavefield features of fin whale vocalization observed by distributed acoustic sensing

Monitoring whale vocalization is of scientific importance and has practical value for marine ecology, hydroacoustics, and geophysics. Conventional monitoring approaches, including hydrophone arrays, ocean-bottom seismometers, and satellite tagging, are limited by sparse spatial coverage, potential biological disturbance, and high cost. Distributed acoustic sensing (DAS) is an emerging method that uses submarine optical cables as dense acoustic arrays, potentially enabling large-scale, high-resolution monitoring of whale vocalization. We investigated the features of the wavefields of fin whale vocalization by integrating DAS observations with numerical modeling. Three distinct features-insensitive response segments (IRSs), high-frequency component loss, and acoustic notches-were identified in the observed wavefields. DAS response modeling based on ray theory indicates that the length of the IRS is correlated positively with the vertical distance between the source and cable, and the gauge length is responsible for the high-frequency loss in whale calls. Furthermore, wavefield modeling using the spectral-element method demonstrates that the notches represent transitions between transmission zones of waterborne multipath waves entering the seafloor and are sensitive to the seafloor P-wave velocity, water depth, and bathymetry. These findings not only improve our understanding of DAS-observed wavefields but also highlight the potential of DAS for ocean environmental parameter estimation and three-dimensional whale localization.