Acoustic interference pattern restoration in shallow water with internal solitary waves based on time-invariant characteristics

Acoustic interference patterns (AIPs) typically exhibit a regular striation structure in shallow water. However, internal solitary waves (ISWs) commonly found in the ocean can cause severe distortion in AIPs, thereby presenting significant challenges to acoustic signal processing methods reliant on AIPs. Grounded in coupled mode theory, this paper elucidates the mechanism of AIP distortion induced by ISWs. Specifically, ISWs introduce several time-varying "coupled" components while maintaining the time-invariant "adiabatic" components. Leveraging the distinct temporal characteristics of these two classes of components, this paper proposes a time-averaging processing (TAP) method. This method averages the AIPs from multiple snapshots to preserve the time-invariant "adiabatic" components while suppressing the time-varying "coupled" components. Consequently, the TAP method restores the distorted AIP to its striation structure. The efficacy of the proposed method is substantiated through validation using simulated data. Moreover, the TAP method provides a foundation for enhancing the performance of underwater acoustic signal processing methods reliant on AIPs.