TOPEX/Poseidon

TOPEX/Poseidon was the NASA-CNES mission that began the modern sea surface height record, launched 10 August 1992 and operating until 2006. It flew two altimeters: the dual-frequency Ku and C-band TOPEX radar from NASA and the experimental single-frequency Poseidon-1 from CNES, sharing one antenna on the 9.9156-day, 1336 km repeat orbit later inherited by Jason. It measured sea surface height to about 4.2 cm, mapping ocean circulation, El Nino, and global mean sea level rise. The reference orbit and cross-calibration scheme it set defined the Jason and Sentinel-6 series that continue the climate-quality record today.