First Data Acquisition and Processing Concepts for the Tandem-x Mission

TanDEM-X is a German Public Private Partnership project between DLR and EADS Astrium for a novel satellite constellation based on TerraSAR-X with the goal to generate a global digital elevation model (DEM) according to the HRTI-3 standard, i.e. 10 m horizontal spacing and 1-2 meter vertical accuracy. TerraSAR-X is a civil German X-Band Synthetic Aperture Radar (SAR) satellite to be launched in 2006 with the purpose to deliver X-Band images for scientific and commercial purposes. The key idea of the TanDEM-X proposal is to place a second TerraSAR-X satellite into the same orbit with a well controlled distance and to operate both satellites in a cooperative way. Our paper describes the TanDEM-X mission and the characteristics of the sensor system. Some special hardware modifications are foreseen on the satellites to enable proper synchronization of the flight paths, the timing of the microwave pulses and the carrier phase. The focus of the paper is on the structure of the SAR data processing chain to be developed at DLR. We describe the strategy of processing the raw data in different phases to a global mosaicked DEM. Intermediate data will be stored in an archive so that calibration or reprocessing with improved parameters or algorithms can be performed with minor impact. The processing will require some new algorithms, such as PRF synchronization, inter-satellite phase trend removal and multi-baseline phase unwrapping. Also the absolute vertical calibration of DEMs to the required 10 meter vertical accuracy will be a challenge.