  We consider an inverse problem of identifying the unknown cavities in a heat
conductor. Using the Neumann-to-Dirichlet map as an input data, we develop a
linear sampling type method for the heat equation. A new feature is that there
is a freedom to choose the time variable, which suggests that we have more data
than the linear sampling methods for the inverse boundary value problem
associated with EIT and inverse scattering problem with near field data.
