UNIQUENESS THEOREMS IN INVERSE OBSTACLE SCATTERING OF ELASTIC-WAVES

We consider the scattering of plane elastic waves in an isotropic homo geneous medium at an obstacle assuming boundary conditions of the firs t kind. We state existence and uniqueness of the direct problem. Then we prove that the far field patterns for a bounded sequence of differe nt frequencies and an incoming plane wave with fixed incident directio n and fixed polarization uniquely determine the obstacle. Finally, we prove the same result for a fixed frequency but for all incident direc tions and a certain set of polarizations.