A uniqueness result for an inverse problem of the steady state convection-diffusion equation

We consider the inverse boundary value problem for the steady state convection diffusion equation. We prove that a velocity field $V$, is uniquely determined by the Dirichlet-to-Neumann map, when $V \in C^{0,\gamma} (\Omega)$, $2/3< \gamma \leq 1$, i.e. when $V$ is a H\"older continuous vector field with $2/3< \gamma \leq 1$.