2025 Excellence in Research Prize and Medal Recipient - Zoi-Heleni Michalopoulou

Eliza Michalopoulou, a mathematician who develops acoustic techniques to reveal uncharted features of the ocean and the movements of its inhabitants, is this year’s winner of NJIT’s Excellence in Research award.

Her field, geoacoustic inversion, uses signal processing and mathematical models to transform underwater sound waves into detailed information about the location of sources such as submarines and whales, and the features of the seabed. She studies how physical properties of the ocean shape the way sound travels beneath the surface.

In work funded by the Office of Naval Research (ONR), she developed improved methods to detect sound from submarines and ocean life, for example, in water up to several hundred meters deep. Typically, these are coastal environments that tend to be especially complex when it comes to identifying the source of a sound and pinpointing its location. The challenge is compounded by the fact that underwater vessels are becoming increasingly quieter, necessitating improved technology for detection and localization.

Many factors influence the propagation of sound in the ocean, notes Michalopoulou, a distinguished professor of mathematics and chairperson of her department. Among them are water temperature, the number of times sound waves bounce between the surface of the ocean and the seabed below, the slope of the ocean floor and its subsurface geologic profile. It’s also necessary to factor in the characteristics of a sound source — sea life or man-made — and the noises of civilization emanating from shore and nearby surface vessels.

Her process relies on underwater microphones, called hydrophones, that capture sound waves. She integrates this acoustic data with mathematical models to understand how sound interacts with the seabed. This helps predict how signals travel through water and what they should ‘look’ like when received. It can also help scientists explore the habitats and migration patterns of marine life.

“By ‘listening’ to the ocean, we can analyze its properties and characteristics without the need to physically deploy extensive equipment into the depths of the vast underwater world,” Michalopoulou said. She also uses machine learning methods, both for sediment characterization and source localization, noting that colleagues share experimental data that facilitates the validation of her methods in real environments.

She notes that in general, the warmer the water, the faster sound will travel between a source and a detector. Accordingly, investigating oceanic sound propagation relative to historic seasonal variations also promises to yield insights into climate change. Sound propagation can be affected by the ocean’s chemical composition as well. Therefore, in addition to climatic information, acoustic analysis can signal changes in the composition of water in a particular area, possibly due to the presence of harmful contaminants.

In recent work backed by the ONR, Michalopoulou is developing techniques to help scientists explore the vast, uncharted and complex ocean floor through sound. To date, nearly 75% of this remote terrain remains unmapped in high resolution.

“Mapping the seabed is a challenging endeavor due to the extreme conditions,” she said. “The immense pressure is crushing at depths like the Pacific’s Mariana Trench, for example, where it reaches over 1,000 times sea-level atmospheric force, making it difficult and costly to deploy submersibles for exploration. The remarkably low temperatures further complicate efforts.”

In 1997, ONR recognized her achievements in ocean acoustics with a prestigious Young Investigator Award.

Michalopoulou is a member of the Acoustical Oceanography, Acoustical Signal Processing, and Underwater Acoustics Technical Committees of the Acoustical Society of America (ASA). She is a Fellow of the ASA and had co-chaired the ASA Women in Acoustics Committee. She is a Senior Member of IEEE, where she is also a Distinguished Lecturer for the Oceanic Engineering Society. She is serving as an associate editor for the Journal of the Acoustical Society of America and the IEEE Journal of Oceanic Engineering.