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

Elizabeth Weidner
Doctoral Dissertation Defense


Thursday, Sep. 15, 2022, 11:30am
Chase 130

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.

Advisors: Larry Mayer, Martin Jakobsson

Committee: Larry Mayer, Martin Jakobsson, Tom Weber, Christian Stranne, Tracy Mandel, Andone Lavery


Elizabeth Weidner graduated from the University of Washington in 2012 with a B.S. in Oceanography. Before coming to CCOM/JHC, she worked as a geophysicist for C&C Technologies. In May of 2018, she received her Master's in Earth Science: Ocean Mapping from the University of New Hampshire with thesis titled: "A wideband acoustic method for direct assessment of bubble-mediated methane flux." She is currently pursuing a Ph.D. in Oceanography in a joint program between the University of New Hampshire and Stockholm University. Her research is focused on the broadband acoustic discrimination and characterization of ocean watercolumn structures.