Inversion of Sound Speed and Thickness of High-Speed Sediment Using Interference Structure in Shadow Zone

The geoacoustic parameter acquisition in the deep sea is of great significance to the research of ocean acoustics. This paper found that the interference structure of the shadow zone induced by the reflection of the high-speed sediment layer could be simply described by the grazing angle of the surface-bottom reflection from the theory of ray acoustics, when the source and receiver depth makes the grazing angle of the surface-bottom reflection consistent with that of the bottom-surface reflection. On this basis, a geoacoustic parameter inversion method by spatial position matching of interference fringes in the shadow zone was proposed, and an interference fringe extraction method was designed based on the maximum between-class variance algorithm in this paper. After extracting the results by the stripe coordinates in the simulation environment, the density was obtained by assuming the base sound speed as an empirical value and combining with Hamilton’s empirical formula, and the sediment sound speed and thickness were inverted by the grid search method. Those inversion results were compared with the multi-dimensional inversion results of the genetic algorithm. The simulation results showed that the fringe extraction method proposed in this paper could effectively extract the interference fringes formed by the reflection of the high-speed sediment in the shadow zone, and compared with the multi-dimensional optimization process, the relatively accurate inversion results of the sound speed and thickness of high-speed sediment could be obtained more effectively and quickly by taking the spatial position of the interference fringe as the cost function of the matching parameter combined with the grid search method in this paper.