The impact of anisotropic roughness on acoustic interaction with the seafloor

Abstract

Accurate description of small scale sediment roughness and its dynamics plays an essential role in the understanding of high-frequency acoustic interaction with the seafloor. The influence of surface waves can be very strong in shallow water, commonly producing relatively large, oriented, and quasi-periodic sediment features, i.e., ripple fields. One-dimensional analysis, which can be limiting in the study of anisotropic seafloors, has traditionally been used to describe sediment roughness spectra. Due to the windowing and averaging operations used to reduce bias at higher spatial frequencies, these studies have usually missed the small bandwidth components that exist. This talk will focus on seafloor roughness and acoustic measurements taken recently on rippled seafloors near Elba Island, Italy. Results of high-resolution two-dimensional roughness measurements obtained with a fully digital close-range photogrammetry system will be presented and compared with previous descriptions of roughness spectra. Acoustic backscatter and penetration measurements, which show a definite sensitivity to the anisotropic nature of the seafloor, will be compared to models that incorporate the measured ripple structure.