The Poseidon-3B altimeter is the primary instrument aboard the joint NASA/French Space Agency/EUMETSAT/ NOAA Jason-3 ocean altimetry mission. The instrument is a dual frequency radar altimeter that measures significant wave height, altimeter range, sigma naught (for radiometric calibration), and ionospheric correction in the Ku (13.575 GHz) and C (5.3 GHz) bands. Launched in 2016, Jason-3 continues the legacy of missions measuring sea level and understanding climate change. Jason-3 is a follow-on to the very successful TOPEX/Poseidon mission, Jason-1 and Ocean Surface Topography Mission (OSTM)/Jason-2.