German X-Band Spaceborne SAR Heritage and the Future HRWS Mission

This paper provides an overview of the German spaceborne radar program starting with the X-band synthetic aperture radar (SAR) instrument on board the Shuttle Imaging Radar missions (SIR-C/X-SAR) in 1994, followed by the Shuttle Radar Topography Mission (SRTM) in 2000. The German national satellite radar program began in 2007 with the launch of the satellite TerraSAR-X, which is providing since then high-resolution X-band images for scientific, commercial and governmental applications. TanDEM-X, an almost identical twin, joined TerraSAR-X in 2010 to form the first bistatic SAR interferometer consisting of two satellites in close formation flight. The TanDEM-X mission generated a global, high-resolution digital elevation model of the Earth surface with unprecedented accuracy. The High-Resolution Wide-Swath (HRWS) mission has been approved for realization at the end of 2020. It is a very ambitious multistatic SAR mission exploiting the formation flight of one active main satellite and three smaller passive companion satellites. HRWS implements for the first time in space the novel MirrorSAR concept. As for the current planning, the launch is expected in 2027.