TerraSAR-X and TanDEM-X Mission Overview and System Status Update

Abstract

TerraSAR-X and its almost identical twin satellite TanDEM-X continue to acquire high resolution radar images and Digital Elevation Models with unprecedented accuracy far beyond their expected lifetime. Since launch the SAR image quality and resolution have remained constant which is owed to a very stable instrument but also to an elaborate ground segment. As a result, the bistatic mission, which was designed for 5.5 years to generate a single global Digital Elevation Model, could be extended. In the following and still ongoing TanDEM-X 4D phase, constant updates of the global dataset are acquired showing in particular the three-dimensional elevation and terrain changes over time. This is performed especially in areas where significant changes are expected as for example in mountainous areas or on glaciers. In this way, the mission has generated a unique dataset by adding change layers to the existing global Digital Elevation Model showcasing natural and man-made topography transformations over the last decade. Furthermore, various timelines could be dedicated specifically to scientific acquisitions focusing on fast changing areas such as forest or permafrost regions and enabling the application of experimental modes such as concurrent imaging. Since both satellites are still in good condition, the ongoing missions will be continued providing continuous updates and extending this unique dataset as long as possible. In order to give an outlook on the remaining lifetime expectancy, this contribution will give a detailed overview of the current status of the systems of the satellites, the remaining onboard consumables and recent as well as upcoming operational challenges. We will present geometric calibration results using on-ground targets as well as antenna pattern measurements and baseline calibration datatakes to demonstrate the excellent radiometric stability of the system. Furthermore, since the battery is the fastest depleting resource, the focus on consumables will particularly be put on the progression of the battery ageing, the assessment of the battery capacity and the implication on the mission planning. For completeness, also the remaining fuel and the according lifetime limitation will be addressed. Additionally, recent events of external and internal nature will be discussed which temporarily affect the position determination and the synchronization of the satellites. In this context, solutions to overcome any correlated acquisitions constraints will be given. In summary the objectives of this contribution are to validate the good condition of both satellites after 14 and 17 years in orbit as well as to demonstrate the strategies and adaptions to extend their lifetime while maintaining image quality.