Echo calculation of targets submerged in a shallow water waveguide based on ray-tracing technique

The geometrical acoustic method calculating echoes from targets submerged in a shallow water waveguide is y profile. A numerical procedure for calculating echoes from complex shaped objects based on ray-tracing technique is developed. The procedure incorporates HAPRO ray-tracing model to obtain eigenrays and planar elements method for scattering calculation. Several numerical examples are given to reveal the echo characteristics in different shallow water environments, especially for two typical velocity profiles in winter and summer, along with two bottom types of fine sand and clay respectively. The results indicate that Equivalent Target Strength (ETS) of a submerged sphere and an elongated cylinder set at cross direction in shallow water are close to their corresponding Target Strength (TS) in the free space. The ordinary active sonar equation is basically valid for this kind of targets which are insensitive to the velocity profile and bottom type. However, when length/wavelength is much larger than 1, ETS of an elongated cylinder set at longitudinal direction and some complicated targets such as benchmark submarine model are remarkably different with TS in the free space, so the ordinary active sonar equation has larger error.