Earth's oceans are the greatest influence on global climate. Only from space can we observe our vast oceans on a global scale and monitor critical changes in ocean currents and heat storage. Continuous data from satellites like TOPEX/Poseidon and Jason help us understand and foresee the effects of the changing oceans on our climate and on catastrophic climate events such as El Niño and La Niña.
How can we measure and track changes in the oceanic heat-budget? We need to know both ocean currents and heat storage of the ocean. Like winds blow around the highs and lows of atmospheric pressure, ocean currents flow around highs and lows of oceanic pressure that can be determined from the height of sea surface, called ocean surface topography. Ocean current velocity can be computed from the slope of the ocean surface. As water heats up, it expands, and as it cools, it contracts, affecting the height of sea surface as well. Measuring the ocean surface topography gives the required information for studying global ocean circulation and the oceans heat budget. Regular scanning of the ocean surface to maintain a database of ocean surface topography can help predict short-term changes in weather and longer- term patterns of climate.
Jason is the successful follow-on to the pioneering TOPEX/POSEIDON mission, which revolutionized our understanding of the dynamics of ocean circulation and global climate. The sea-surface height measurements begun by TOPEX/POSEIDON in 1992 and now carried on by Jason provide an unprecedented 13-year-long record of consistent, continuous global observations of Earth's oceans. An early calibration phase of the mission allowed TOPEX/POSEIDON and Jason to fly over identical ground tracks. For the first time, two radar systems fly simultaneously over the same location, providing a unique opportunity to cross calibrate the spacecraft instruments to remove systematic errors. The resulting data stream provides seamless coverage between the two missions. This coverage allows scientists to observe and study both short-lived events such as hurricanes and long- term climate phenomena such as the Pacific Decadal Oscillation. It also provides the capability to monitor global mean sea level, an indicator of global temperature change. This calibration experiment provides the first demonstration of how overlapping missions enable a long-term consistent data record.
Jason-1 has been designed to directly measure climate change through very precise millimeter-per-year measurements of global sea-level changes. The Jason-1 satellite, its altimeter instrument and a position-tracking antenna have been built in France. The spacecraft will also carry a radiometer instrument to measure water vapor, a Global Positioning System receiver and a laser retroreflector array built in the United States. Jason-1 was launched in December 2001 from California's Vandenberg Air Force Base.
Weighing 500 kilograms (about 1,100 pounds), Jason-1 is one-fifth the size of Topex/Poseidon. After launch, Jason-1 will fly in tandem with Topex/Poseidon, doubling the science data return for as long as Topex/ Poseidon remains in good health. Jason-1 will then assume Topex/ Poseidon's former flight path. The mission is planned to last for five years.
The science objectives for Jason-1 and its successor missions are now expected to: