Meridional and helical ray contributions to backscattering by tilted cylindrical shells: High-frequency tone burst and wide bandwidth measurements and interpretation

Abstract

When viewed in the frequency-angle domain, the backscattering by truncated thick cylindrical shells in water exhibit various ridges of high backscatter. These enhancements are associated with leaky waves excited on the shell and can be described in terms of meridional and helical rays. The enhancements are not present for a rigid scatterer of the same shape and may be important for interpreting high-frequency sonar echoes. Previous work [Morse et al., J. Acoust. Soc. Am. (to be published)] has shown that these enhancements are not limited to near broadside incidence but can extend to end-on incidence in the coincidence frequency region. Results of broadband and tone burst measurements of these enhancements are presented. High-frequency tone bursts may be used to separate the meridional ray enhancement from the generally weaker helical ray enhancement. The general angular width of the meridional ray enhancement may be explained using an approximate ray theory [Marston, J. Acoust. Soc. Am. 102, 358–369 (1997)]. The amplitude of the backscattered meridional ray depends on the leaky wave reflection coefficient at the end of the cylinder which appears to be affected by mode conversion near mode thresholds. [Work sponsored by the Office of Naval Research.]