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On the first anniversary of the launch of the joint U.S.French TOPEX/Poseidon satellite, early results indicate that sea level measurements taken by the satellite are even more accurate than expected.

TOPEX/Poseidon, launched Aug. 10, 1992, has been measuring the global sea surface height using a radar altimeter system. Precise measurements of sea surface height are needed for the study of the dynamics of large-scale ocean circulation. Ocean circulation plays a major role in global climate by transporting heat from the equator to the poles and the ocean may be an important key to long-term global change.

"The verification results indicate that all the measurement objectives have been met and many measurements have exceeded performance requirements," said Charles Yamarone Jr. the TOPEX/Poseidon project manager at NASA's Jet Propulsion Laboratory. "In fact, the accuracy of sea surface height measured by the satellite is about 5.7 centimeters, which is significantly better than the 13.4-centimeter requirement."

TOPEX/Poseidon is the first satellite mission to provide such precise and accurate observations of sea level and these data allow scientists to study complex global ocean dynamics. Eventually, scientists will use the TOPEX/Poseidon data to help them determine how ocean currents contribute to world-wide climate change.

"The primary objective for the first six months of the mission was to calibrate and validate the mission's measurements," said Dr. Lee-Lueng Fu, JPL TOPEX/Poseidon project scientist.

"During the second six months in orbit we mapped sea level changes and showed those changes to be caused by seasonal warming and cooling and wind," Fu added. "We need three to five years of this kind of high quality data to make major advancements in our knowledge of the circulation of the world's oceans."

TOPEX/Poseidon is also the first satellite mission that distributes high-quality sea level data to scientists in a timely manner for both scientific and environmental monitoring. "The 38 principal investigators from nine countries are currently analyzing TOPEX/Poseidon data to study currents in every corner of the world's oceans," Fu said.

The resurgence of the El Ni┬Ło phenomenon in the equatorial Pacific last spring was just one example of the wide range of studies conducted by TOPEX/Poseidon mission scientists. Many of the science team members are also participants of the Tropical Ocean and Global Atmosphere program (TOGA) and the World Ocean Circulation Experiment (WOCE) which are world-wide programs that study the ocean and atmosphere.

TOPEX/Poseidon data will be used with findings from WOCE and TOGA to establish an extensive database for the computer modeling of ocean circulation. The ocean models will eventually be coupled with atmospheric models and will enable scientists to predict global climate change, Fu explained.

TOPEX/Poseidon was launched by an Ariane 42P booster rocket from the Arianespace Guiana Space Center in Kourou, French Guiana.

JPL manages the U.S. portion of the mission for NASA's Office of Mission to Planet Earth.

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