Upcoming Event: PhD Dissertation Defense

Differentiable acoustic propagation in ocean general circulation models for variational state estimation

Ivana Escobar, CSEM Ph.D. Candidate

Abstract

Direct ocean observing systems provide the primary constraints on the present understanding of the ocean state, but remain sparse in regions of strong hydrographic variability and at depth. Acoustic travel times offer a complementary observing approach by measuring the integrated thermal structure of the ocean along long propagation paths between sound sources and receivers. Despite their observational value, acoustic propagation models are typically applied offline using static ocean environments, limiting their integration with modern ocean circulation models and data assimilation systems.

 

This dissertation develops a computational framework that embeds acoustic ray tracing within the MIT general circulation model (MITgcm), enabling dynamic coupling between evolving ocean states and acoustic travel time predictions. The acoustic solver computes eigenray travel paths and arrival times using geometric ray tracing in a range-dependent ocean environment. By integrating the acoustic operator directly within the circulation model, the framework provides a consistent mapping from ocean state variables to acoustic observations, allowing travel times to be analyzed alongside conventional ocean observing systems.

 

Algorithmic differentiation is applied to the coupled ocean–acoustic model to compute forward-mode sensitivities of acoustic quantities of interest to perturbations in the ocean state. Verification experiments using idealized wind-driven gyre configurations demonstrate accurate tangent linear sensitivities of mean sound speed and acoustic travel times. An acoustic model–data misfit cost function is then formulated within a variational assimilation framework using synthetic travel time observations. The resulting framework establishes a differentiable pathway for incorporating acoustic travel time measurements into ocean state estimation and data assimilation systems.

 

Biography

Ivana Escobar is a CSEM Ph.D candidate at the Oden Institute supervised by Prof. Patrick Heimbach and Dr. Feras Habbal. Her research in ocean sciences includes coupling ocean circulation and underwater acoustic models, assimilating oceanic observing systems, and developing scalable simulations for HPC environments. Her undergraduate studies in Mechanical Engineering were completed at the University of Texas at San Antonio. Ivana also has a M.S. in Structural Engineering from the University of California, San Diego and a M.S. in CSEM from the Oden Institute.