Abstract
The scattering strength of isotropic and anisotropic rough surfaces was experimentally and theoretically investigated for high frequencies about 500 kHz. Emphasis was placed on studying the response from three two-dimensional rough surfaces which roughness was either isotropic (characterized by a Gaussian distribution) or anisotropic (characterized by a modified-sine surface). Theoretical predictions rely on the first-order small slope approximation either including a Gaussian structure function or a quasi-periodic structure function. The combination of true data and theoretical results indicates the importance of taking into account the anisotropy of a surface in a scattering prediction process. It is shown that the scattering strength varies a lot depending on the propagation plane. In the longitudinal direction of ripples, scattering strength is mostly in the specular direction, whereas in the transversal direction of the ripples, the scattering strength is spread in a very different way related to the particular features of the ripples, with several maxima and minima independent of the specular direction. Contrary to the isotropic surface, the scattering strength from an anisotropic rough surface is modified from one propagation plane to another, which explains why the entire rough surface should be taken into account without any simplification as it is often seen when dealing with scattering models. Compared to such a surface, positions of the emitter and of the receiver are naturally significant when measuring scattering strength.
Highlights
Acoustics scattering from the ocean bottom is a subject of interest for many remote sensing acoustic sensing marine activities, such as seabed classification, or ecosystem habitat mapping [1,2]
Contrary to the isotropic surface, the scattering strength from an anisotropic rough surface is modified from one propagation plane to another, which explains why the entire rough surface should be taken into account without any simplification as it is often seen when dealing with scattering models
Jackson and coworkers [10,11,12] have modified the monostatic method to obtain a bistatic model which only works for isotropic surfaces. This model was used by Choi et al [13,14] for comparing theory with real data obtained from their measurements above ripple field. Their comparisons showed that the orientation of the measurement plane compared to the direction of the ripples has a great effect on the scattering, the scattering strength distribution being very different from one propagation plane to another over the ripples
Summary
Acoustics scattering from the ocean bottom is a subject of interest for many remote sensing acoustic sensing marine activities, such as seabed classification, or ecosystem habitat mapping [1,2] To these purposes, high frequency tools, as single beam or multibeam echosounders or side scan sonars, are used to assess the bottom roughness and improve the knowledge of the environment [3,4]. Jackson and coworkers [10,11,12] have modified the monostatic method to obtain a bistatic model which only works for isotropic surfaces This model was used by Choi et al [13,14] for comparing theory with real data obtained from their measurements above ripple field. This method has been elaborated as a unifying method able to reconcile small perturbations method and Kirchhoff approximation [16]
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