TOPEX

TOPEX, short for Topography Experiment and commonly referred to as the TOPEX/Poseidon mission, was a joint satellite mission by NASA and CNES (the French space agency) designed to map the world’s ocean surface topography with high precision. Its primary objective was to measure sea surface height globally over a long, continuous record in order to study ocean circulation, mesoscale dynamics, and climate variability.

The mission carried the Poseidon radar altimeter, which emitted radar pulses toward the ocean surface and measured the round-trip travel time to determine the distance between the satellite and the sea. When combined with precise satellite orbit information and atmospheric corrections, these measurements produced sea level data with centimeter-level accuracy, referenced to a global sea level baseline. The resulting data set enabled detailed mapping of ocean currents, sea level anomalies, and large-scale oceanic patterns.

Launched in 1992, TOPEX/Poseidon operated for more than a decade, contributing a foundational global sea surface height record used by researchers to advance oceanography and climate science. The mission’s success helped establish satellite radar altimetry as a critical tool for understanding the Earth’s oceans and informed subsequent missions.

Legacy and influence: TOPEX/Poseidon paved the way for the continuation of satellite altimetry through later missions in the Jason program (and related missions), which extended and expanded the capability to monitor global ocean topography. Data from TOPEX/Poseidon remain in NASA and CNES archives and continue to support scientific research and model development related to ocean circulation and climate.