Impacts of a freshwater input and variable surface profile on shallow water acoustic propagation

Freshwater input from rivers, glacial melt, or precipitation can introduce a shallow, low-salinity layer to the upper water column, affecting acoustic propagation throughout the medium. Here, the change in surface layer salinity and temperature decreases the sound speed at the top of the water column, and thus alters the acoustic propagation physics. Additionally, sea surface variability induced by tidal fluctuations and sea surface roughness can modify the signal-to-noise ratio through acoustic scattering and variability in transmission paths. This study investigates how a low-salinity surface layer, sea state variability, and tidal effects can jointly modify the acoustic propagation behavior in shallow marine environments. Using statistical methods, we analyze how the presence of a surface freshwater layer and increasing sea surface roughness impact both transmission loss and signal-to-noise ratio. The results provide insight into upper boundary layer effects and inform acoustic system performance in dynamic surface conditions.