TerraSAR-X SAR Data Processing: Results from Commissioning and Early Operational Phase

Kurzfassung

TerraSAR-X, the first national German radar satellite, was launched June 15, 2007. SAR data taking and image generation started as early as four days after launch. The commissioning phase was completed in December 2007 with the basic product release for StripMap and Spot-Light mode, ScanSAR product release will follow in February 2008. Since beginning of 2008, basic products from all modes are provided to the scientific and commercial user community. Due to a comprehensive system validation testing performed pre-launch on ground including both, the ground and space segment, the TerraSAR-X mission experienced an extraordinary smooth transition into the commissioning phase. Thousands of data takes were acquired and provided to the verification team already in the first months. All level 1b user products are generated with the high-precision phase-preserving TerraSAR Multi-Mode SAR processor TMSP developed by the Remote Sensing Technology Institute of DLR (using a geocoding plug-in component provided by the German Remote Sensing Data Center). This does not hold for the ground segment itself, but also exclusively for the commercial direct access stations. Focus of its commissioning phase check-out was its fitness to deal with TerraSAR-X in-orbit SAR data characteristics which could not be assessed pre-launch on ground, namely the signal Doppler behaviour, calibration pulse processing influences and the resulting range and azimuth focusing quality in low and high contrast scenes. With the help of a detailed Doppler analysis, the correct working of the Total Zero Doppler Steering law applied during attitude control was shown. An observed beam mispointing with respect to the spacecraft attitude reference sys-tem was corrected based on Doppler deduced correction values. A major commissioning phase activity was the qualification and verification of the various SAR basic products for the science and commercial users, a challenging task considering their multi-tude in terms of complex and detected product types from the various imaging and polarization modes which span a wide range of incidence angles. Specific care was given to their geometrical accuracy and phase-preserving characteristics which promise to support new exciting applica-tions using TerraSAR-X. The suitability of high-resolution TerraSAR-X data for interferometric processing was shown already in July 2007 as soon as the first repeat-pass data takes were available. Not only standard StripMap, but also SpotLight interferometry – a novelty in spaceborne SAR imaging - was dem-onstrated using the GENESIS interferometry system developed by and operated at DLR’s Re-mote Sensing Technology Institute. An example over an urban area is presented.