Broadband acoustic characterization of backscattering from a rough stratification interface

Abstract

Broadband acoustic analysis of scattering from sharp density gradients in the water column generally treat the interfaces as smooth surfaces. However, these interfaces may exhibit roughness owing to external water column forcing and local convective processes. In this work we extend broadband backscatter analysis methods to consider interface roughness by drawing upon methods developed for sea surface and seabed acoustic backscattering. The one-dimensional acoustic model from Weidner and Weber [J. Acoust. Soc. Am. 150(6), 4353–4361 (2021)], which predicts a decay in the reflected wave amplitude from stratification interfaces with increasing frequency, was expanded for surface applications. The expanded model was used to analyze the scattered pressure field from interfaces over a range of surface roughness magnitudes. Analysis of model results indicate that stratification interface roughness, quantified by the root-mean-squared interface slope angle and root-mean-squared height of the interface, modifies the model-predicted frequency-dependent backscattering. A broadband acoustic inversion procedure to remotely measure the magnitude of the vertical extent of stratification gradients and the corresponding sound speed perturbation was defined. The broadband inversion method was tested on data collected in the Baltic Sea with well-documented, strong salinity-driven stratification.