The effects of roughness on the frequency dependence of specular scattering.

Abstract

Specular scattering data were collected at grazing angles from 7 to 77 deg grazing and frequencies from 5 to 50 kHz at the experimental validation of acoustic modeling techniques (EVA) sea test near Isola in October 2006. High resolution microbathymetry data taken using a laser line scan system were also collected. The amplitude and phase of the specular scattered data exhibit a distinctive frequency dependence. This frequency dependence may be due to Bragg scattering from small interface ripples on the ocean bottom indicated by peaks in the measured interface roughness power spectrum. This study simulates the scattering using realizations of interface roughness in a finite element model to determine if the frequency dependence is due solely to scattering or if other mechanisms such as layering are important factors. Results will be compared to analytic approximations such as the Kirchhoff approximation as well as exact integral equations. [Work sponsored by the ONR, Ocean Acoustics.]