Georg-August-Universit¨ at G¨ottingen Fast Methods for Three-Dimensional Inverse Obstacle Scattering Problems Helmut Harbrecht and Thorsten Hohage Preprint Nr. 2005-35 Preprint-Serie des Instituts f¨ ur Numerische und Angewandte Mathematik Lotzestr. 16-18 D - 37083 G¨ottingen