Precise Orbit and Baseline Determination for TerraSAR-X and TanDEM-X

TerraSAR-X (TSX), the recent German radar satellite launched on June 15, 2007, carries as primary instrument a synthetic aperture radar (SAR) sensor. The GFZ German Research Centre for Goesciences and the Center for Space Research (CSR) at the University of Texas in Austin, USA, provided the Tracking, Occultation and Ranging Category A instrument package (TOR) to the TSX mission to enhance the quality of the scientific SAR products and to collect occultation measurements for atmospheric/ionospheric sounding. The TOR consists of a precise dual frequency GPS flight receiver (Integrated GPS and Occultation Receiver - IGOR) and a Laser retro- reflector (LRR) that supports Satellite Laser Ranging (SLR) observations from the Earth's surface. Also the CHAMP and GRACE satellites are equipped with the LRR originally developed for CHAMP by GFZ. TanDEM-X (TDX), a twin to TSX, to be launched in September 2009 will fly with TSX in a tandem orbit configuration. Its compatible SAR system enables bistatic application for the derivation of digital elevation models (DEMs). For TDX, GFZ again supplies the TOR payload. The IGORs on both satellites will become the key to the continuous determination of the baseline (the distance of the two individual SAR antennae) with millimeter accuracies. In this paper, we concentrate on results gained so far for TSX precise orbit determination (POD) and on the status of our preparations for precise baseline determination (PBD) for the tandem mission.