Abstract
The first-order small slope approximation is applied to model the scattering strength from a rough surface in underwater acoustics to account for seafloor for high frequencies from 10 kHz to hundreds of kilohertz. Emphasis is placed on simulating the response from two-dimensional anisotropic rough surfaces. Several rough surfaces are described based on structure functions such as the particular sandy ripples shape. The scattering strength is predicted by the small slope approximation and is first compared to a well known bistatic method, interpolating the Kirchhoff approximation and the small perturbations model, assuming that the rough interface is isotropic. Results obtained from the two different models are similar and show a higher level in the specular direction than in the other directions. For an isotropic surface, changing the propagation plane gives similar results. Then, SSA, which lets us adapt the structure function of the roughness straight away, is tested trough several anisotropic surfaces. In a longitudinal direction of ripples, the scattering strength is mostly in the specular direction, whereas in the transversal direction of ripples, the scattering strength prediction shows high values for different angular directions. Thus the scattering strength is spread in a very different way strictly related to the particular features of the ripples. Combine our results, indicates the importance of taking into account the anisotropy of a surface in a scattering prediction process, taking into account the positions of the emitter and of the receiver which are naturally significant when predicting scattering strength.
Highlights
Acoustics scattering from the ocean bottom is a subject of interest for many remote sensing acoustic sensing marine activities, such as classification of seabed, or mapping of ecosystem habitat [1,2]
We address the effects of seabed roughness with particular attention being given to simulation of the two-dimensional height structure function
In a smoother direction of the surface, the scattering strength obtained considering one propagation plane would be spread around the specular direction
Summary
Acoustics scattering from the ocean bottom is a subject of interest for many remote sensing acoustic sensing marine activities, such as classification of seabed, or mapping of ecosystem habitat [1,2]. The investigation of the interest and efficiency of one of these models, the so-called Small Slope Approximation (SSA) is addressed in this paper This choice has been made based on the possibility of taking into account different types of rough surface as well as due to the direct link between roughness and scattering which of importance in a perspective of roughness inversion, for predicting roughness trough scattering data. To take into account the anisotropy of the seabed, which is the basic motivation of this paper, the small slope approximation, originally developed by Voronovich [15], is interesting since it allows to consider various anisotropic rough interfaces via the two-dimensional structure function. We discuss the effects of the relief on the predictions of the roughness scattering strength
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