TanDEM-X is a mission proposal for a TerraSAR-X add-on satellite for high-resolution single-pass SAR interferometry. This mission proposal has been selected for a Phase A study within the scope of a Call for Proposals for a next German Earth Observation Mission to be launched in 2008/2009. The mission has the goal of generating a global Digital Elevation Model (DEM) with an accuracy corresponding to the DTED-3 specifications (12 m posting, 2 m relative height accuracy for flat terrain). This goal will be achieved by means of a second, TerraSAR-X like satellite (TanDEM-X) flying in a close orbit configuration with TerraSAR-X. This paper describes the mission concept and requirements, including several innovative aspects like operation modes, orbit selection and maintenance as well as PRF and phase synchronization. Results from a detailed performance estimation show the achievable DEM accuracy. Finally, an overview of the potential of the TanDEM-X mission for several scientific applications is presented.

Systematic and statistical errors cause a significant degradation in the performance of polarimetric radar and antenna measurements. This paper presents a complete 12-term error model for the systematic errors in polarimetric free space measurements, as there are the frequency response, channel imbalance, the coupling between the transmit channels, the coupling between the receive channels, the coupling from transmit to receive and finally the residual reflections of the environment. The errors are contained in three 2*2 matrices, the isolation matrix [I], the transmit matrix [TI, and the receive matrix [RI. A full polarimetric calibration with the empty room, a sphere, a vertical dihedral corner and a 45" dihedral corner is proposed. The physical understanding is supported by a cubic signal graph for the error terms.

This paper reports about the status of the actual performance prediction and some selected investigations within the system engineering for the TerraSAR-X satellite, which will be implemented in a Public-Private-Partnership between the German Aerospace Center (DLR) and the ASTRIUM GmbH. The main sensor parameters and modes of operation are summarized. Image simulations based on X-band data from the E-SAR sensor of DLR give an impression on the expected image quality with respect to geometric and radiometric resolution. Different realization possibilities for the dual polarization mode are investigated and the actual baseline for this mode is described. The potential of two independent receiving channels is analyzed and the paper reports about possible additional features as investigated so far.

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