Abstract
We consider the inverse problem to recover a part c of the boundary of a simply connected planar domain D from a pair of Cauchy data of a harmonic function u in D on the remaining part partial derivative D\Gamma(c) when u satisfies a homogeneous impedance boundary condition on Gamma(c). Our approach extends a method that has been suggested by Kress and Rundell [17] for recovering the interior boundary curve of a doubly connected planar domain from a pair of Cauchy data on the exterior boundary curve and is based on a system of non-linear integral equations. As a byproduct, these integral equations can also be used for the problem to extend incomplete Cauchy data and to solve the inverse problem to recover an impedance profile on a known boundary curve. We present the mathematical foundation of the method and illustrate its feasibility by numerical examples.