Complex spherical waves and inverse problems in unbounded domains
  We consider the inverse conductivity problem of identifying embedded objects in unbounded domains. The main tool is a set of special solutions to the Schroedinger equation, the complex spherical waves, which are constructed by a Carleman estimate. Using these solutions we can treat the inverse problem in the unbounded domain like in the bounded case, and it is possible to localize the boundary measurements to a finite part of the boundary. 
Mikko Salo and Jenn-Nan Wang