Jason 1

The Jason 1 satellite altimeter is a science project to measure the ocean surface topography, and the successor to the TOPEX/Poseidon satellite. It is a joint project between the NASA (United States) and CNES (France) space agencies. It was launched on December 7, 2001 aboard a Boeing Delta II. During the first months Jason 1 shared an almost identical orbit to TOPEX which allowing for cross calibration. At the end of this period TOPEX was moved to a new orbit midway between each Jason ground track. Like TOPEX, Jason has a repeat cycle of 10 days. The program is named after the Greek mythological hero Jason. It contains 5 instruments:

• Poseidon 2 - Nadir pointing Radar Altimeter using C band and Ku band for measuring height above sea surface.
• Jason Microwave Radiometer (JMR) - measures water vapor along altimeter path to correct for pulse delay
• DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) for orbit determination to within 10 cm or less and ionospheric correction data for Poseidon 2.
• BlackJack Global Positioning System receiver provides precise orbit ephemeris data
• Laser retroreflector array works with ground stations to track the satellite and calibrate and verify altimeter measurements.

Use of information

A number of satellites (See links) use exotic dual-band radar altimeters to measure height from a spacecraft. That measurement, coupled with orbital elements (possibly from GPS), enables determination of the topography. The two lengths of radio waves permit the altimeter to automatically correct for varying delays in the ionosphere. Over water, detailed satellite altitude information has proven amazingly useful. Humps in the water indicate gravitational concentrations, permitting a computer program to construct a maps of undersea features such as mountains. The altimeters can also measure wave heights, wave directions, and wave spectra. This information permits computer programs to measure the speed of ocean currents and produce detailed maps of wind speeds and directions at the surface, even in extremely stormy conditions.

See also

• Argo, a project to measure the temperature and salinity of the upper 2 km of the water column.
• Seasat- an early radar altimeter satellite
• TOPEX/Poseidon- the immediate predecessor to Jason 1.
• Ocean Surface Topography Mission - the planned successor to Jason 1.
• 2004 Indian ocean earthquake (Energy of the earthquake)

External links

• Jason site at CNES
• TOPEX/Jason site at NASA
• DEOS: The Radar Altimeter Database System (RADS)

This article contains material that originally came from a NASA website. According to their site usage guidelines, "NASA material is not protected by copyright unless noted". For more information, please review NASA's use guidelines.