Acoustic propagation at low-to-mid-frequencies in the Connecticut River

An estuary is a constrained environment which often hosts a salt wedge during flood and a fresh water plume on ebb, the structures of which are complex functions of the tide’s range and speed of advance, river discharge volumetric flow rate and river mouth morphology. A field experiment was carried out in the Connecticut River in June 2017, one goal of which was to investigate the low-to-mid-frequency acoustic propagation characteristics of the riverine salt wedge as well as the plume outside the river mouth. Linear frequency-modulated (LFM) acoustic signals in the 500-2000 Hz band were collected during several tidal cycles. Data analyses demonstrate the degree to which these features in this highly energetic environment impact acoustic propagation; dominant mechanisms are boundary interactions, salt wedge sound speed gradients and bubble clouds at the ebb plume front.