Earth is an ocean planet. The oceans cover nearly three-quarters of the world's surface, store most of earth's available hear and carbon dioxide, and play a central role in determining global climate trends. These trend, or climate changes, affect the earth's temperature and rainfall, which in turn impact crops and industry. In recent years scientists have discovered that they can obtain a continuous, comprehensive look at the surface of world's oceans by using a satellite in space equipped with an instrument called an altimeter.

Actual Image from the TOPEX/POSEIDON satellite.
Thanks to NASA/JPL/Caltech for this image.

In 1979, NASA's Jet Propulsion Laboratory began planning TOPEX, an Ocean Topography Experiment that would use a satellite altimeter to measure the surface of the world's oceans. At the same time the French space agency Centre National d'Etudes Spatiales (CNES) was designing an oceanographic mission called Poseidon, named for the Greek god of the Sea.

The two space agencies decided on a cooperative effort and pooled their resources to form a single mission. The result is the highly-successful TOPEX/Poseidon which has achieved science objectives beyond expectations and at a lower cost that either mission would have achieved separately.  The satellite has continously surveyed the oceans' surface currents with radar altimeters since launch in 1992. The satellite orbits Earth 4 700 times per year, and engineers are optimistic that the missoin will continu to collect data through at least Septemeber 1998. 

Building on three earlier earth-orbiting missions TOPEX/Poseidon - a joint mission between the US and France - is part of a global oceanographic effort to acquire a comprehensive look at the world's oceans. TOPEX/Poseidon's contribution involves continuous observations of the surface currents of the ocean.

TOPEX/Poseidon is based on earlier earth-orbiting satellite missions. The earliest missions provided proof of the concept that some ocean observations can be made more economically and with better coverage from space than from the earth's surface. Each mission carried a different complement of instruments and discovered new facts that inspired successive missions and generations of spacecraft.