Ray trace modeling of three-dimensional propagation at the New England Seamounts

Out-of-plane propagation resulting from acoustic interactions with abruptly varying bathymetry is often difficult to predict and can make the disentanglement of noise and reverberation from multipath propagation challenging. As a case study of these effects, an airgun survey conducted during the New England Seamounts Acoustics Experiment is analyzed for the presence of out-of-plane arrivals associated with prominent bathymetric features of the Atlantis II Seamount Complex. Time delay analysis is applied to a set of three near-bottom acoustic recorders to assess the directionality of distinct arrivals in the received time series. Back propagation using three-dimensional (3-D) ray tracing facilitates the identification of bathymetric features associated with the arrivals. Predicted propagation paths are recreated by combining two-dimensional ray traces from the source to the bathymetric feature and from the bathymetric feature to the receiver to obtain modeled arrival times for comparison with observations. Multiple examples of out-of-plane reflections from specific bathymetric features on the slope and near the base of the seamount are identified, providing insight into likely contributors to the complex propagation in seamount environments. Forward modeling of the identified propagation paths using 3-D ray traces highlights challenges for ray-based acoustic modeling of propagation in the presence of highly variable bathymetry. [Work supported by ONR.]