In this paper we present the inverse scattering obstacle problem considering incident spherical waves. The incident spherical waves have a source set outside the obstacle zone. Density theorems are obtained for these type of incident waves and some kind of source sets. The uniqueness for the inverse obstacle problem is proved in this framework and some other relations are obtained. Namely, a reciprocity relation and a relation with the scattering cross section.

CEMAT - Center for Computational and Stochastic Mathematics