A direct inverse scattering method for imaging obstacles with unknown surface conditions

A new technique is described for imaging obstacles using the acoustic far "eld response for plane wave incidence. The method requires no a priori information about the surface, nor does it depend upon prior knowledge of the surface boundary conditions. The algorithm is straightforward to implement and is illustrated by imaging multiple targets simultaneously for various surface boundary conditions: soft, hard, and impedance. The input data is the full acoustic scattering matrix at a single frequency, from which the eigenvalues and eigenfunctions of the far "eld operator are determined. Associated incident wave functions are then used to compute a spatial indicator function which takes on large values in the exterior of the target but is bounded inside the obstacle, or obstacles when there are multiple disconnected surfaces.