Identification of parametric models for ultrasonic reflection experiments performed on sediments at oblique incidence

Reflection of bounded ultrasonic beams at oblique incidence from viscoelastic material in controlled measurement conditions is described using a combination of complex harmonic plane waves (CHW model). Previous work was carried out in this field at normal incidence. The shear properties of materials cannot be determined by the normally incident experiment using an immersion technique. This paper gives an extension by modelling wave propagation at oblique incidence using the magnitude as well as the phase of the incident ultrasonic field. A maximum likelihood estimator (MLE) is constructed for the estimation of the model parameters, which takes the measurement noise on both the input and the output signals into consideration. From the estimated model parameters, the absorption and dispersion properties and velocities for both shear and longitudinal waves as well as the density of the sample medium are obtained simultaneously. In order to guarantee that only the material properties are identified, the calibration of the measurement set-up is incorporated in the estimation approach.