“…Uniqueness also holds for isotropic elastodynamics [12], [13], [14], and, up to the natural obstruction, for isotropic media with residual stress [15], [16]. Hansen and Uhlmann [16] use a microlocal analytic approach to the study of reflection of singularities to prove that the scattering relation at the surface is determined by the Dirichlet-to-Neumann map, which extends Rachele's result [15] to the case that caustics are present. In addition, Robertson shows that the Dirichlet-to-Neumann map uniquely determines the residual stress tensor and one of the Lamé parameters at the boundary [17], and establishes uniqueness in the interior [18] for the linearized problem using Man's model [19] for residual stress.…”