Using an autonomous surface vehicle to survey low-frequency acoustic propagation near Atlantis II seamounts

Deepwater abrupt topography changes, such as seamounts, can significantly enhance the complexity of underwater sound propagation by notably creating highly variable three-dimensional scattering effects, thus making it more challenging to predict numerically. One avenue to precisely survey the spatial variability of deep-water sound propagation induced by isolated seamounts is to use instrumented autonomous surface vehicles (ASV) that can be accurately geo-located. These precise acoustic observations can, in turn, be used to validate numerical model predictions in these complex environments. Here, an ASV called Wave Glider was equipped with a hydrodynamic towed acoustic module (TAM) to survey the spatial variability of low-frequency acoustic propagation across the Atlantis II seamounts in the Northwest Atlantic. The TAM was deployed along the Gulf Stream boundary and crossed over the Atlantis II seamounts, which significantly influenced the TAM’s recordings of chirp transmissions (500–600 Hz band) from a bottom-moored source ∼30 km from the seamounts by notably causing blockage of in-plane propagation paths and complex reverberation arrivals displaying three-dimensional effects, as confirmed by synthetic aperture beamforming. 2-D and 3-D ray-tracing simulations are performed with input sound speed fields computed from the outputs of a data-assimilated ocean model to compare with experimental observations. [Work Supported by ONR.]