Direct and Inverse Problems in Ocean Acoustics: Propagation, Physics-Based Processing and Applications
Monday February 3th 2025 at 14:00
Wolfson Building of Mechanical Engineering, Room 206
Abstract:
The undersea world presents a fascinating yet challenging environment for sensing, with acoustics serving as the primary tool due to the limited propagation of electromagnetic waves in seawater. Sound, however, can travel vast distances underwater, sometimes propagating thousands of kilometers under specific conditions. Yet, the ocean’s highly inhomogeneous nature, characterized by strong spatial and temporal variability, creates a highly complex acoustic environment, posing significant challenges for both direct and inverse problems in ocean acoustics.
This seminar explores these challenges by addressing one direct and one inverse problem, each in drastically different acoustic environments. First, we investigate how internal Kelvin gravity waves impact sound propagation in shallow water. Through analysis of experimental data from Lake Kinneret and advanced sound propagation modeling, we demonstrate that internal Kelvin waves can cause a significant, fourfold decrease in sound intensity over a 5-km acoustic track — an important consideration for underwater communication and defense applications.
The second part of the seminar moves to the Challenger Deep, the Earth’s deepest point, where we employ a synthetic aperture autonomous recording system to address an inverse problem. Here, we demonstrate how wind-driven ambient noise can be leveraged to infer ocean acidity — a critical concern due to its impact on marine ecosystems. By analyzing the depth-dependent attenuation of sound and applying the principles of passive absorption spectroscopy, we showcase a novel method for estimating the volumeintegrated pH of seawater
Bio:
Ernst began his academic journey studying Nuclear Physics and Technology in Russia before making Aliyah and pursuing his Master’s and PhD studies in Underwater Acoustics in Haifa University under the supervision of Prof. Boris Katsnelson, graduating with honors. His research involved extensive experimental work in Lake Kinneret and Mediterranean Sea, focusing on sound propagation in shallow and deep water affected by spatial and temporal inhomogeneities. At the latest stage of his PhD, Ernst received the prestigious Batsheva de Rothschild scientific grant and served as a Visiting Researcher at the Naval Postgraduate School, where he studied single-element time-reversal mirrors.
He later transitioned to nonlinear acoustics, conducting postdoctoral research on parametric acoustic and receiving arrays at the Technion’s Department of Mechanical Engineering under supervision of Prof. Izhak Bucher. Following this, Ernst undertook another postdoctoral position at Dalhousie University in Canada, developing deep-ocean noise spectroscopy methods using data from an autonomous synthetic aperture ocean profiler under the supervision of Dr. David Barclay.
Currently, Ernst is conducting postdoctoral research at the Naval Postgraduate School in the United States under supervision of Prof. Oleg Godin, supported by a grant from the National Academy of Sciences. He is actively involved in the New England Seamounts Acoustic Experiment, investigating acoustic propagation and associated diffraction and refraction effects around prominent bathymetric features.
Ernst is a member of the Acoustical Society of America and its Technical Committee on Acoustical Oceanography. He has chaired sessions at Acoustical Society of America meetings and serves as a reviewer for leading journals, including the Journal of the Acoustical Society of America, Applied Acoustics and the Journal of Sound and Vibration and.
