An Inverse Kinematic Problem with Internal Sources
  Given a bounded domain $M$ in $\mathbb{R}^n$ with a conformally Euclidean metric $g=\rho\,dx^2$, in this paper we consider the inverse problem of recovering a semigeodesic neighborhood of a domain $\Gamma\subset \partial M$ and the conformal factor $\rho$ in the neighborhood from the travel time data (defined below) and the Cartesian coordinates of $\Gamma$. We develop an explicit reconstruction procedure for this problem. The key ingredient is the relation between the reconstruction and a Cauchy problem of the conformal Killing equation. 
Leonid Pestov, Gunther Uhlmann, Hanming Zhou
math.DG math.AP