A time-evolution model of seafloor scatter is numerically implemented and experimentally evaluated. The model is based on analytically expressing the elementary time-backscattered response of every seafloor surface and every seafloor volume infinitesimal element. The implementation of the model is based on a statistical realization of the seabed interface and volume inhomogeneities, from which the time series are computed by coherent summation of the scatter from small elements over the insonified area and volume. The analytical expressions and the implementation are evaluated for the image solution case, for which an almost perfect agreement is found. Examples are shown of how the beam width and seabed roughness affect the time-series return from both the surface and from the volume. The results of the model are compared with data from two different bottom types recorded with a parametric sonar. Reasonable accordance is found between the model and the data.
A time-series model for acoustic seafloor backscattering is described. The method analytically expresses the elementary time-backscattered response of every seafloor surface and every seafloor volume infinitesimal element. For chosen geometric, acoustical, and acquisition parameters, they are summed to produce in the time domain a realization of the reverberation time-pressure field received at the source. The approach is based on the Kirchhoff approximation for the seafloor interface backscattering and on the Small Perturbation theory for the seafloor volume. It only accounts for single backscattering mechanisms of the compressional wave with the seafloor. The model is implemented using calculated height fields for the water-sediment interface and distributed seafloor volume inhomogeneities. The analytical description of the model and its limitations is described in this paper.
Parametric sonars are instruments capable of transmitting acoustic signals in the water with a very narrow beam and almost no sidelobes. These features are exploited in this paper to define a methodology for quantitative estimation of the geo-acoustic and morphological properties of the uppermost seafloor sediment layer. The three major components of the approach are the parametric instrument itself; the modelling of the forward-propagation problem, with the use of the Kirchhoff approximation for surface scattering and of the small-perturbation theory for the volume scattering; and the definition of a criterion for comparison between data and model predictions, which is accomplished by a generalized time-frequency analysis. In this way the estimation becomes one of a model-based identification, or a model-based inverse problem. Results from a field trial in a shallow water area of the Mediterranean are shown, and compared with independently gathered ground truth.
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