TerraSAR-X Instrument Calibration Results and Extension for TanDEM-X

Spaceborne remote sensing with synthetic aperture radar (SAR) has become an essential source of high-resolution and continuous earth observation. Modern satellites like the German TerraSAR-X system provide radar images of unprecedented service with respect to operating flexibility and imaging quality. The outstanding performance of TerrSAR-X image products is achieved by an innovative calibration approach that minimizes systematic antenna and instrument characteristics. The active phased array X-Band antenna is fed by 384 transmit/receive modules for electronic beam steering and shaping in azimuth and elevation direction. The flexible radar instrument hosts an internal calibration system which guarantees the high radiometric stability of all SAR products. New techniques for antenna performance control have been successfully implemented setting a high standard for next-generation SAR missions. This paper summarizes all essential calibration results of TerraSAR-X that cover internal instrument behavior. Furthermore, we give an outlook on the required bistatic calibration techniques for the future TanDEM-X mission that faces additional performance challenges when calibrating two TerraSAR-X satellites flying in close formation

Traceable Radiometric Calibration of Synthetic Aperture Radars

Synthetic aperture radar (SAR) systems allow to quantitatively measure the radar backscatter of an imaged terrain region. In order to achieve comparability between measurement results, traceable radiometric calibration is indispensable. The central claim of the work is that nowadays, however, radiometric SAR measurements are not traceably calibrated. In order to resolve this problem, five contributions are made: (a) The new measurement quantity “equivalent radar cross section” (ERCS) is defined. (b) A numerical approach for linking the known quantity “radar cross section” (RCS) with the novel ERCS is introduced. (c) The effect of the chosen apodization functions on radiometric measurements is analytically investigated. (d) The novel three-transponder method is developed which allows accurate RCS calibrations of SAR transponders. (e) The method of hierarchical Bayesian data analysis is introduced to the field of radiometric SAR calibration. The achieved traceability for radiometric SAR measurements allows more accurate radiometric measurement results especially for modern, high-resolution SAR systems. Furthermore, data exchange and cooperation is facilitated