Estimation of modal properties for shallow-water underwater sound propagation using normalized active intensity

The active acoustic intensity vector describes the net flow of acoustic energy and can be directly measured using co-located pressure and velocity sensors. By normalizing the active intensity with the received signal’s potential energy, the influences of source excitation and range dependence are minimized for low-frequency and impulsive signals, enabling direct comparison of measurements taken at different ranges. These normalized values are shown to be proportional to modal wavenumbers, providing a means to characterize the acoustic waveguide. Measurements from explosive SUS charges and ship tonals collected during the 2022 Seabed Characterization Experiment are analyzed to extract modal properties and compared with model predictions. This approach enables the direct measurement of modal wavenumbers, offering insight into water–sediment interactions in shallow-water acoustic propagation.