Development of the highly accurate DLR Kalibri Transponder

Upcoming spaceborne synthetic aperture radar (SAR) missions like the Sentinel-1 mission pushing the limits toward better image quality especially in radiometric accuracy. Highly accurate calibration of the instrument is one of the key factors on this way. Therefore the DLR has developed a novel, very stable, and exactly characterized transponder called Kalibri. Three of these remote controlled transponders will be installed on a calibration area of more than 400 km2 in southern Germany. In this paper the challenges and solutions for the development with respect to accuracy, reliability and stability are presented.