Status of DLR’s C-band Calibration Transponders and Outlook on an Upgrade for future SAR Missions

Abstract:
For more than 25 years, DLR’s SAR Calibration Center has supported the calibration of a large number of spaceborne SAR missions. For ESA’s Sentinel 1 mission, launched in 2014, three active reference targets, called “Kalibri” transponders, were developed and manufactured in-house. These transponders were used for an independent calibration of the Sentinel-1A and -1B satellites. Since then, the radiometric and polarimetric calibration of both SAR instruments has been monitored by routine overpasses with all three targets. In order to ensure the availability of the C-band transponders until the end of the mission and to be well prepared for follow-on missions such as Sentinel-1 Next Generation, DLR has already started with the design of a comprehensive facelift of these “Kalibri” transponders. This paper provides an outlook on the planned transponder upgrade and gives an overview of the current status of DLR’s C-band transponder activities.