The Layer That Didn’t Swim Away: Broadband Acoustic Characterization of Oceanic Stratification Structure

TitleThe Layer That Didn’t Swim Away: Broadband Acoustic Characterization of Oceanic Stratification Structure
Publication TypeThesis
AuthorsWeidner, E
Degree and ProgramDoctor of Philosophy
Date PublishedSeptember 2022
UniversityUniversity of New Hampshire
LocationDurham, NH

Ocean stratification structure plays a critical role in many oceanographic processes. The magnitude of mixing between stable water masses is regulated, in part, by the intensity of stratification. As such, stratification structure modulates the vertical transport of heat and many important dissolved constituents in the water column, influencing such processes as ocean ventilation, and ocean heat and carbon uptake. As human induced climate change alters oceanic stratification structure a thorough understanding of its the distribution and variability is critical in the study of the world’s oceans. However, traditional methods are limited in terms of spatial context and rapid, synoptic observational methods, such as those provided by active acoustic systems, are needed to fill in the gaps.

Broadband acoustic water column data have already been used to observe ocean structure and commercial systems are becoming increasingly available. However, broadband acoustic methods for characterizing oceanic stratification structure are not well developed, limiting of applicability of broadband data to the study, quantification, and monitor ocean stratification structure as the world warms. This thesis aims to develop quantitative acoustic methods for characterization of ocean stratification structure using active broadband acoustic systems.

This work leveraged the high range resolution and signal to noise ratios, as well as the frequency-modulated scattering response of broadband acoustic systems. Broadband acoustic methods were developed and established through 1) the analysis of field data from different ocean basins and 2) the development and application of acoustic scattering models. This work will provide the means to better understand the physical mechanisms responsible for acoustic backscattering from stratification structure, working towards rapid, remote, high-resolution measurements of ocean stratification structure through acoustic inversion, in order to monitor and quantify changes in ocean structure.