Mechanism interpretation and validation of stable interference fringe characteristics for multi-static near-bottom suspended targets

To quantitatively describe complex echo-spectrum interference fringes and key peak features under multipath coupling between flat-seabed interface reflection and target scattering, this study establishes a two-dimensional finite element model for a flat seabed and investigates the scattering characteristics of suspended targets under multi-static conditions. Based on multipath geometry and phase-interference analysis, the physical mechanism by which stable spectral interference fringes are formed by phase differences among dominant scattering paths is clarified. Based on the Biot–Stoll poroelastic theory, coarse-sand and clay seabed models were established to investigate the effects of grazing angle and target suspension height on the interference-fringe structure and scattering strength. The numerical results show that the overall distribution of the dominant interference fringes remains relatively stable under different seabed conditions, while seabed properties have a more pronounced influence on echo-intensity levels. Meanwhile, the seabed reflection phase and target elastic-scattering phase may induce local shifts in the peak positions. On this basis, a key-peak prediction method for interference fringes is proposed based on multipath geometric relationships, enabling quantitative characterization of fringe peak position, number, and intensity under the effects of suspension height and grazing angle. The effectiveness of the method is validated by scaled water-tank experiments.