Parametric modelling and estimation of acoustic sediment properties using a system identification approach

The acoustic properties (absorption, dispersion) of marine sediments are measured as a signature of the mechanical characteristics of marine-estuarine sediments. Accounting for this signature, the sediment´s grain size composition, porosity, permeability, viscosity, mineralogy, and physico-chemical environment of deposition seem the controlling factors. In this paper a parametric modelling and estimation approach is presented for acoustic reflection and transmission experiments on natural sediments performed at normal incidence using a controlled measurement environment (frequency range [300, 700] kHz). Since it has been shown that absorption and dispersion in a nearly linear homogeneous isotropic viscoelastic material can be modelled by means of a rational form, L. Peirlinckx et al. (1993), a similar approach was followed for modelling the sediments. Although marine sediments do not fulfil the constraints of isotropy and homogeneity, it is known that their mechanical behaviour lays in the domain of viscous, elastic, or a combination of both responses to applied stresses of various characteristics, and in L. Bjorno (1977), evidence is given of the nonremarkable acoustic non-linearity of marine sand and silt assemblages, as compared to their high attenuation of energy. By this work it could be demonstrated that the proposed modelling approach is valid, certainly for acoustically identifying fine grained, low viscous mud