Revealing the Wavefield Features of Fin Whale Vocalizations Observed by Distributed Acoustic Sensing

Monitoring fin whale (Balaenoptera physalus) vocalizations is of significant scientific importance and practical value for marine ecology, hydroacoustics, and geophysics. Conventional monitoring approaches, such as hydrophone arrays, ocean-bottom seismometers (OBS), and satellite tagging, are limited by sparse spatial coverage, potential biological disturbance, and high costs. Distributed acoustic sensing (DAS) is an emerging technology that utilizes submarine optical cables as dense acoustic arrays, providing opportunities for large-scale, high-resolution monitoring of whale vocalizations. Here, we reveal the wavefield features of fin whale vocalizations by integrating DAS observational data combined with numerical simulations. Three distinct features—Insensitive response segment (IRS), high-frequency component loss, and acoustic notch—were identified in the observed wavefield. DAS response analysis via ray-acoustic modeling indicates that the length of the IRS is positively correlated with the vertical source-to-cable distance, while the gauge length is responsible for the high-frequency loss in Type-B calls. Furthermore, wavefield simulations using the spectral-element method (SEM) demonstrate that the acoustic notches represent transitions between transmission zones of waterborne multipath waves entering the seafloor, exhibiting high sensitivity to the seafloor P-wave velocity, water depth, and topography. These findings not only enhance our understanding of the DAS-observed wavefields, but also highlight the potential of utilizing DAS and acoustic notches for ocean environmental parameter estimation.