Bistatic and interferometric processing of TanDEM-X data

The German TanDEM-X mission flies the two satellites TerraSAR-X (TSX) and TanDEM-X (TDX) in a close orbit formation establishing a bistatic interferometer in space. Primary mission goal is the generation of a global Digital Elevation Model (DEM). The SAR data, jointly acquired by both satellites, are operationally processed by the Integrated TanDEM-X Processor (ITP). Processing comprises bistatic synchronization and focusing, filtering, co-registration, phase unwrapping and geocoding. Outputs are individual scene (50km × 30km) based digital elevation models (DEM) and co-registered phase preserving single look slant range complex SAR images (CoSSC). Furthermore, SAR data acquired in new and experimental acquisition modes, the second mission goal, are processed to CoSSCs as well. The experiences of more than one year TanDEM-X data processing and calibration have been incorporated as refinements of algorithms and workflows. The paper presents the operational ITP processing chain with a special focus on phase and delay corrections of the bistatic SAR raw data as well as algorithmic improvements with respect to phase unwrapping and tropospheric delay corrections.