Launch: August 10, 1992
Mass: 2,500 kilograms (about 5,510 pounds)
Dimensions: 2.8 by 5.5 meters (9.2 by 18 feet), plus solar panel 3.3
by 8.7 meters (10.8 by 28.5 feet)
Science instruments: Altimeters, microwave radiometer, Global Positioning System receiver,
Doppler tracking receiver, laser retroreflector
JPL's Seasat mission established that a satellite could use radar pulses
to measure its altitude from Earth's surface. Taken over the world's oceans,
these measurements could provide a high-fidelity view of the changing heights
of the seas. That became the focus for the joint U.S.-French Topex/Poseidon
Under the joint plan between NASA and France's National Center for Space Studies
(known as CNES for its acronym in French), the United States provided the satellite,
altimeter, a microwave radiometer, an experimental satellite tracking receiver and
various spacecraft subsystems. France supplied launch on an Ariane 42P rocket
from French Guiana in South America, as well as two instruments on the satellite -- a solid-state
altimeter and a Doppler tracking receiver. Topex is short for "Ocean Topography Experiment,"
the name of the original U.S. mission proposal, while Poseidon was the name of the original
French mission proposal.
From its orbit 1,336 kilometers (830 miles) above Earth's surface,
Topex/Poseidon measures sea level every 10 days using the altimeter instruments
developed by NASA and CNES. Using this information, scientists can relate changes in
ocean currents to atmospheric and climate patterns. Measurements from
the satellite's radiometer provide estimates of the total water-vapor
content in Earth's atmosphere, which is used to correct errors in the altimeter
measurements. These combined measurements allow scientists to chart the
height of the seas across ocean basins with an accuracy of less than 10
centimeters (4 inches). Although originally planned for a three- to five-year
mission, Topex/Poseidon continues to operate nine years after its launch.
Among other science findings, Topex/Poseidon provided a unique view of the El Niño
phenomenon of the late 1990s, an unusual water warming in the eastern Pacific Ocean.
That El Niño was followed by a rebound effect of cold water conditions that
came to be known as La Niña.
The satellite was built for JPL by Fairchild Space Co.
For more information, see the
Topex/Poseidon home page or the
Oceanography from Space fact sheet.