TOPSAR is a recently proposed SAR mode for wide swath acquisition, which is foreseen to be used by the ESA Sentinel-1 SAR sensor in its main interferometric wide swath mode. The Microwaves and Radar Institute of the German Aerospace Center is validating TOPSAR mode in space with TerraSAR-X data within the framework of an ESA commissioned project. Several TOPSAR images have been successfully commanded, acquired and processed. First TOPSAR images are presented. A pair of TOPSAR data takes over a high coherent area (the Uyuni salt lake in Bolivia which has already shown good phase stability with 11 days repeat pass TerraSAR-X acquisitions) has been acquired and preliminary interferometric results are presented in the paper. Coregistration accuracy requirements are discussed.