Bruce Haines (Jet Propulsion Laboratory, California Institute of Technology, USA ); Shailen Desai (Jet Propulsion Laboratory, California Institute of Technology, USA)

Sentinel-6 mission has been launched in November 2020. It is the first altimetry mission with explicit requirements for the accuracy of Global Mean Sea Level drift. In support of this goal, JPL has developed a transponder that allows for an accurate monitoring of the altimeter.
This transponder is the first instrument of its kind to operate in both the Ku and C bands. It will therefore allow for a full calibration of range and power of both altimeter channels.
We present a summary of the instrument design and characteristics along with results from the flyovers during the tandem phase with Jason-3.