Underwater environments, like the seafloor, can be better understood by analyzing how they reflect transmitted acoustic signals. In acoustic terms, the seafloor is a sediment–water interface whose impedance change disrupts the incident signal structure. Sonar systems can also capture sub-bottom reflections from the sediment volume and any underlying sediment organization, i.e. sub-bottom layers. This work uses the spatial coherence of the scattered field to understand environmental structures and variations that are sensitive to the seabed composition. Spatial coherence is a metric of similarity between two spatially separated signal receptions and is represented by coherence length (σ). Specifically, coherence length is the separation distance between two measured points for their correlation coefficient (ρ) to fall below their peak correlation coefficient divided by e. Previous work used maximum likelihood estimation (MLE) of ρ and σ to estimate coherence length. Extensions of the previous work may reduce bias and increase the method’s utility for sensing spatial coherence. Results are validated on synthetic data and compared to previous work. Finally, extensions to the previous coherence length estimation techniques are applied to measurements made by a Kongsberg SBP-29 aboard R/V Sally Ride in 2024.
Brownstead et al. (2025) studied this question.