TerraSAR-L SAR Parameter Simulation

Abstract

The TerraSAR-L system, currently being designed in a Phase B definition study, will provide ESA with its most powerful radar-imaging programme to date. The platform, based on a Snapdragon configuration, is optimized for and built around the 11 m x 2.9 m active phased array antenna of the L-band Synthetic Aperture Radar (L-SAR). The L-SAR features, on top of standard Stripmap and ScanSAR operations, full polarimetric capabilities, repeat-pass ScanSAR interferometry and a Wave Mode. The TerraSAR-L spacecraft flies in a near-polar sun-synchronous low Earth orbit. An attitude steering operation to reduce the Doppler frequency caused by the Earth’s rotation is foreseen. The knowledge of the relative distance between the spacecraft in orbit and a point scatterer on Earth during the radar illumination time, the so-called slant range history, is a crucial input for SAR focusing. Usually, this trajectory is approximated by an appropriate function. The validity of the approximation within the required accuracy margins has to be ensured. The applied attitude steering is a major driver for the Doppler parameters and thus the allowed approximations. This paper introduces the major TerraSAR-L orbit parameters and imaging configurations. Based on the nominal Kepler reference orbit, the round-orbit Doppler characteristics for TerraSAR-L are derived. The DLR developed Total Zero Doppler Steering is investigated as a suitable candidate for the TerraSAR-L attitude steering. A range trajectory approximation is investigated.