ASA 125th Meeting Ottawa 1993 May

4pUW2. On the acoustic probing of the sea bottom in shallow water from near-field data.

Marc Lambert

Dominique Lesselier

Lab. des Signaux et Systemes CNRS-ESE, 91192 Gif-sur-Yvette Cedex, France

The probing of the acoustic profiles of the seabed in shallow water from the sound pressure observed on a line array in presence of a cylindrical source, is dealt with. The seabed is modeled as a depth-inhomogeneous fluid sediment overlying an homogeneous fluid subbottom. As is well known, the propagation is characterized by the depth-dependent Green's function in the horizontal wave-number (spectral) domain, which is a function of the plane wave reflection coefficient of the seabed, with extension to wave numbers larger than the one of water. Conversely, seabed parameters are sought by analyzing features of the Green's function, such as location and magnitude of peaks with then measurements needed in the far field. Here, using receivers near the source, where the ``continuum'' part of the field is preponderant, directly provides an estimate of the reflection coefficient (at least at low wave numbers). This allows the application of solution methods of the 1-D inverse scattering problem, with limitations due to the discrepancy between estimate and true coefficient. Corresponding issues: retrieving the reflection coefficient, probing the parameters profiles, are investigated and illustrated by examples taken in various source, array, and seabed configurations.