Acoustic scattering from rough elastic cylinders partially insonified by directional sonars: Effects of rms roughness and correlation length

A modal-series-based model for acoustic scattering from smooth and rough elastic cylinders insonified by directional sonars is derived. Sonar directivity, Fresnel zone effects, spherical spreading of the incident field, and axially propagating guided waves excited by this spreading are included while end-effects are assumed to be negligible. The performance of the scattering model is evaluated against laboratory monostatic and bistatic measurements of scattering from both smooth and rough elastic cylinders. Three aspects of scattering — overall scattering levels, resonance frequencies, and resonance shapes — are analyzed both theoretically and experimentally. The roughness on the cylinder has a Gaussian distribution and is characterized by a random variation of the cylinder radius along its length. Effects of various statistical properties of this one-dimensional roughness, such as different rms roughness for a given correlation length and different correlation lengths for fixed rms roughness, are investigated.