Broadband acoustic characterization of backscattering from a rough stratification surface

Abstract

This work aims to elucidate the utility and limitations of broadband scientific echo sounders in characterizing the frequency-dependent scattering from stratification interfaces. A recently published 1D acoustic backscattering model for the oceanic stratification structure was expanded for this work to consider echo sounding applications and the importance of roughness (vertical and spatial variability) along the stratification interface. The expanded model was tested in utilizing data from a recent acoustic experiment in the Kattegat basin, a region with well-documented, strong, salinity-driven stratification. A suite of broadband split-beam echosounders (45–270 kHz) provided broadband backscattering data, which were validated using high resolution in situ observations of water column structure, collected with a CTD (Conductivity, Temperature, Depth) sensor and MVP (Moving Vessel Profiler). Overall, the frequency dependence of backscattering agrees with model predictions of a gradual decay in the reflected wave amplitude from stratification structure with increasing frequency. Stratification interface roughness drives changes in frequency-dependent scattering away from a smooth surface solution as a function of different roughness regimes, primarily defined by the root-mean-squared slope of the interface. Results suggest a path to remote estimations of physical medium properties through broadband acoustic inversion.