# Ten Years of TerraSAR-X Operations
## 1 Introduction  
On 15 June 2007, the first national German radar satellite TSX was launched from the Russian Baikonur Cosmodrome in Kazakhstan, which marked the starting point for the highly successful TerraSAR-X remote sensing mission [1]. This mission has now lasted for more than 10 years and achieved remarkable results. Despite a satellite age well beyond its nominal life time of 5.5 years, no significant technical flaws were encountered. The objective of providing high-quality SAR products in Spotlight, Stripmap, and ScanSAR mode variants with various polarizations [2] has since been met without any restrictions and the image quality is just as good as it was at the beginning of the mission. The reasons for the outstanding long-term performance are both the excellent manufacturing of the satellite systems [3] and the design of the ground segment [4] tuned to it, i.e., which is able to exploit all of the capabilities of the satellite bus and the radar instrument. This could already be seen during the launch and early orbit phase. Only four days after launch, the first SAR images were successfully acquired, downlinked, and processed on ground using nominal ground segment workflows. At the end of 2007, the complete SAR system was characterized and calibrated, the SAR products were verified and the ground segment was operationally qualified [5]. Over ten years of operations, the TerraSAR-X system underwent to a certain extent an evolutionary process. Although the TerraSAR-X ground segment, as described in [4], has maintained its basic structure throughout the mission, it has been steadily improved and expanded upon to meet new requirements. The biggest impact had its upgrade to serve a second mission on top, the TerraSAR-X Add-On for Digital Elevation Measurements TanDEM-X, starting in 2010. The primary TanDEM-X mission goal was the generation of a global digital elevation model (DEM) of Earth's total land mass within two years. A second satellite TDX, which is almost identical to TSX, was launched on 21 June 2010. Both satellites since then fly in a close configuration with a minimum distance of about 250 m and perform together bistatic radar acquisitions of the Earth's surface, as required for the DEM generation. Both satellites are also used, either TSX or TDX, to acquire the monostatic acquisitions for the on-going TerraSAR-X mission. The necessary modifications, extensions and tests to implement the TanDEM-X functionalities into the ground segment meant a massive intervention comparable with open-heart surgery, since the ongoing operation of the TerraSAR-X mission was not allowed to be interrupted or disturbed. Commissioning of the TDX system was accomplished in October 2010 and the joint TerraSAR-X/TanDEM-X ground segment was successfully released for TerraSAR-X operations that are based on two satellites flying in a close formation. Driven by science and commercial business cases, new products, services and capabilities were required, leading to a number of operational extensions and improvements. * The SAR imaging mode and thus product portfolio has been extended in 2013 by Staring Spotlight and Wide ScanSAR. The first of these improves the obtainable azimuth resolution to about 24 cm, while the second provides an extended swath width of about 200 km. * The experimental dual-receive antenna configuration provides full polarimetric imagery and along-track interferometry acquisitions. * The overall receiving station capacity and flexibility has been increased. * Near-real time support has been improved by shortening the turn-around times and by introducing new data sets for maritime applications. Radar science is one of the driving forces that aim to extend existing or to test new radar modes and to put theoretical considerations into practice. The flexible design of the radar instrument provides the conditions for numerous experiments.