Underwater Distributed Acoustic Sensing of Ship-Associated Hydrodynamic Wavefields and Surface Gravity Waves

Abstract We characterize ship-associated wavefields and its relation to background surface gravity waves (SGW) on two underwater distributed acoustic sensing (DAS) arrays, one ∼11 km cable at the Foziling reservoir in Anhui, China, and another ∼20 km cable offshore seafloor cable near Yantai in Shandong, China. In the Foziling reservoir, ship-generated signals are separated into mechanical and propeller-related tones, and the 2–10 Hz hydrodynamic noise driven by relative motion between the ship and water. At the Yantai offshore ocean-bottom DAS, higher-frequency ship tones decay rapidly, but the 2–10 Hz hydrodynamic waves remain clear. As ships cross the cable, we observe enhanced energy at ∼0.09 to 0.19 Hz and at ∼0.9 to 1.25 Hz in the Foziling Reservoir, and ∼1.3 to 1.6 Hz at Yantai. Frequency–wavenumber analysis indicates that these enhancements are associated with relative propagation directions between the ship-driven hydrodynamic forcing and background SGW, which is likely due to second-order nonlinear interaction between them. These observations offer insights into dynamic waves caused by waveway transportation and help understand the complex wavefields recorded by underwater DAS.