Andrew Niedbala
Master’s Thesis Defense
Ocean Engineering
Wednesday, August13, 2025, 10:00 a.m.
Chase 130
Abstract
Seafloor sediment characterization is of interest to many, including those studying benthic environments, pursuing offshore development, and improving national defense capability. This thesis describes the development of a geoacoustic inversion to resolve seafloor sediment characteristics and is designed for use with existing fisheries survey single beam echosounder (SBES) datasets. The geoacoustic inversion consists of a forward model and inversion algorithm. The forward model is a high frequency (18-120 kHz) physics-based near normal incidence Kirchhoff approximation based acoustic backscatter model enhanced with a density depth gradient model and geoacoustic sediment regressions. The inversion algorithm is a parallel tempered Markov-chain Monte Carlo Bayesian inversion. The geoacoustic inversion produces posterior probability distributions for mean grain size, density, porosity, sound speed, seafloor roughness characterization, and sediment volume scattering description.
Two datasets are used in this study: a calibrated multi-frequency EK60 scientific SBES dataset collected by the National Oceanographic and Atmospheric Administration and a seafloor sediment sample dataset collected by the United States Geological Survey and the University of New Hampshire. The combination of these two datasets provides thousands of geographically co-located pairs of acoustic and sediment data. The geoacoustic inversion uses the 18, 38, and 120 kHz frequency SBES data and is validated by comparison to sediment sample mean grain size.
The inverted mean grain size results agree with ground truth samples for sands, while predicting a finer mean grain size than ground truth samples for silts and clays. The evaluation of density depth gradients is inconclusive. The work is the foundational for inversion application to fisheries survey calibrated SBES datasets for mass seafloor characterization with existing data.
Bio
Andrew Niedbala graduated from the United States Coast Guard Academy in 2019 with a degree in Civil Engineering. From 2019 to 2021, he served on CGC Escanaba (WMEC 907) as a deck watch officer along with several other roles, including assistant operations officer and navigator. From 2021 to 2023, he served as executive officer aboard CGC Donald Horsley (WPC 1117), homeported in San Juan, Puerto Rico. Andrew is currently a Lieutenant in the United States Coast Guard and is pursuing an M.S. in Ocean Engineering: Ocean Mapping. Following graduation, Andrew will return to benefit the USCG with his degree. Andrew currently lives in Boston with his wife, Anna, and loves hiking and spending time in and on the ocean.
