Impacts of a multi-ayered acousto-elastic bottom on sound propagation in a seamount environment

The New England Seamounts Acoustics (NEMSA) experiment is a comprehensive oceanographic field study aimed at investigating underwater acoustic propagation and scattering effects within a complex marine environment. The primary objective of this research is to assess the influence of seafloor and sub-bottom geoacoustic properties on acoustic propagation, signal reflections, and transmission loss at Atlantis II Seamount. Two advanced acoustic models, BOUNCE and BELLHOP, were employed to incorporate elastic wave effects within the sub-bottom layers and facilitate the analysis of range-dependent bathymetric features. Two model scenarios were analyzed and compared, one with a layered elastic bottom and another with a fluid bottom assumption. The outputs from these two models were assessed by comparing them to data measured by the Ocean Bottom Recorders (OBX) during the field experiment. BOUNCE results show complex interaction of interference patterns for both shear and fluid cases at specific frequencies and grazing angles. Frequencies below 500 Hz show the most difference in bottom loss between the fluid and shear cases. BELLHOP results indicate the strong alignment between the model and hydrophone data arrival times, as well as frequency spectrum interference patterns. Work sponsored by ONR.