Foreword to the Special Issue on TerraSAR-X: Mission, Calibration, and First Results

T ERRASAR-X is Germany's first civil radar satellite. It has been realized in a public–private partnership between the German Aerospace Center (DLR) and EADS Astrium GmbH. The high-resolution synthetic aperture radar (SAR) satellite, which was successfully launched on June 15, 2007, delivers high-quality radar images for scientific and commercial applications. TerraSAR-X is the fruit of consistent development of German radar technology over many years and is an example of successful cooperation between the DLR and the German space industry. More than 45 000 data sets have been acquired and processed since the launch of the satellite. The image product quality is exceeding all specifications and setting new standards for future spaceborne SAR missions. The high stability of the sensor, the high precision of the calibration, the demonstration of new imaging modes, and the outstanding geolocation accuracy of the images are examples of highlights already achieved with TerraSAR-X during the commissioning phase. In this last decade, more than 15 SAR satellites have successfully been launched for scientific, commercial, and security-related applications. SAR is an indispensable source of information in Earth observation since spaceborne SAR is the only imaging sensor that has all-weather and day-and-night high-resolution imaging capability. SAR already plays a major role in a wide spectrum of applications as for 2-D, 3-D, and 4-D (space-time) mapping, environmental monitoring, retrieval of bio/geophysical parameters of land, ocean, and ice surfaces , hazard and disaster monitoring, and reconnaissance and security-related applications. Information extraction has achieved a mature and operational level in a number of fields, making the contributions of SAR systems to present and future programs like GMES and GEOSS an indispensable one. In the last few years, we have entered a new era of space-borne SAR systems. New satellites like TerraSAR-X, COSMO-Skymed, Radarsat-2, TanDEM-X, and Sentinel-1 provide or will provide radar images with a resolution up to 100 times better than the one of conventional SAR systems. They are also outperforming by far existing systems with respect to their imaging flexibility and interferometric modes. These SAR satellites open new fields for scientific use of radar data. A golden age for spaceborne SAR systems has just started. The objective of this Special Issue is to give an overview of the TerraSAR-X mission, commissioning phase, calibration, data processing, and applications. Several examples of application results achieved by the international science community are presented. You will find some " firsts " related to technology demonstration, …