Acoustic scattering of submerged targets from head waves in a shallow-water waveguide

This paper establishes a scattering model for elastic targets under head wave incidence to address the localization and identification requirements for long-range detection of submerged targets in a shallow-water waveguide. Expressions for multiple head waves are derived using the ray theory. The scattered field of the target in the waveguide is obtained by integrating the scattering separation method (SSM) with multiple head waves. Scattering in both free-field and waveguide environments for submerged (suspended and bottomed) vacuum elastic spherical shells under head wave incidence is calculated. The results indicated that (1) the bistatic scattered acoustic field under head wave incidence exhibits asymmetry that is positively correlated with frequency and sediment attenuation. This characteristic changes the typical “X-shaped” distribution of the flexural wave a0- in the bistatic impulse response into a “\-shaped” distribution. When the target is bottomed, multiple scattering effects between the interface and the target interfere with this transformation. (2) Due to the rapid propagation characteristics of the head wave, the first-arrival rigid echo from the spherical shell in the waveguide can be accurately utilized for target localization when received by a vertical line array (VLA). In addition, the elastic echo effectively extracts the resonance peak of the a0-wave, enabling further identification of target parameters such as radius and shell thickness ratio.