Acoustic Normal Mode Dispersion using Superlets

The waveguide boundaries play critical role in influencing acoustic propagation and this factor is especially important in shallow water. Accurate bottom properties must be known to understand and model acoustic propagation in shallow water. The continental shelves are typically dominated by coarse grained sediments (sand and silt) and their acoustic properties (sound speed and attenuation) has been the focus of research in recent years. Compared to coarse grained sediments much less is known about the properties of fine grained sediments (clay/mud) and their impact on acoustic propagation. Experiments were conducted in an area, with a surficial layer of fine-grained sediments, called New England Mud Patch, in the continental shelf of US East Coast, in 2017 and 2022. Broadband data from the 2022 experiment is analyzed in this study. A new time-frequency analysis technique called superlets is applied to identify dispersed acoustic normal modes and extract modal arrival times. The modal arrival times are used to infer the bottom properties. The inverted bottom model compares well with other estimates of bottom properties from the experimental area.