Launched in 1992, TOPEX/Poseidon was a joint satellite mission between NASA, the U.S. space agency, and CNES, the French space agency, to map ocean surface topography. The first major oceanographic research vessel to sail into space, TOPEX/Poseidon helped revolutionize oceanography by proving the value of satellite ocean observations. The distinguished oceanographer Walter Munk described TOPEX/Poseidon as "the most successful ocean experiment of all times." A malfunction ended normal satellite operations January 2006.

Before TOPEX/Poseidon, scientists had only a brief glimpse of Earth's ocean as a whole from the pioneering, but short-lived Seasat satellite. TOPEX/Poseidon' radar altimeter provided the first continuous global coverage of the surface topography of the oceans. From orbit 1,330 kilometers above Earth, TOPEX/Poseidon provided measurements of the surface height of 95 percent of the ice-free ocean to an accuracy of 3.3 centimeters. The satellite's measurements of the hills and valleys of the sea surface led to a fundamental new understanding of ocean circulation and its effect on climate.

Poseidon (Greek: Ποσειδῶν) is one of the twelve Olympian deities of the pantheon in Greek mythology. His main domain is the ocean, and he is called the "God of the Sea". Additionally, he is referred to as "Earth-Shaker" due to his role in causing earthquakes, and has been called the "tamer of horses".

The name of the sea-god Nethuns in Etruscan was adopted in Latin for Neptune in Roman mythology; both were sea gods analogous to Poseidon. Linear B tablets show that Poseidon was venerated at Pylos and Thebes in pre-Olympian Bronze Age Greece, but he was integrated into the Olympian gods as the brother of Zeus and Hades. There is a Homeric hymn to Poseidon, who was the protector of many Hellenic cities, although he lost the contest for Athens to Athena.

The earliest attested occurrence of the name, written in Linear B, is Po-se-da-o or Po-se-da-wo-ne, which correspond to Poseidaōn and Poseidawonos in Mycenean Greek; in Homeric Greek it appears as Ποσειδάων (Poseidaōn); in Aeolic as Ποτειδάων (Poteidaōn); and in Doric as Ποτειδάν (Poteidan), Ποτειδάων (Poteidaōn), and Ποτειδᾶς (Poteidas). A common epithet of Poseidon is Γαιήοχος Gaiēochos, "Earth-shaker," an epithet which is also identified in Linear B tablets.