4st PART


Weekly height ocean surface

Around our blue planet have been putting satellites into orbit satellites (Jason, Topex-Poseidon...) orbit to measure the height of the oceans with their altimeter at few centimeters near. It is from this information it is possible to know what is going on in depth : the density of water, salinity, temperature, and therefore the currents.

So from these data are provided and monitored the movement and extent of El Nino or La Nina.....

TOPEX-POSEIDON and JASON I and II of the NASA / CNES are satellites that measure the weekly height of the sea surface (SSH) with high accuracy and oceanic currents. The instantaneous accuracy average of the local estimate of the ocean level is better than 5 cm, and the average precision on a month better than 2 cm.

Here are the main satellites measuring or measured the level... of the oceans :

FROM 10/08/1992 TO 12/07/2001

FROM 15/09/2001 TO 2008

FROM 20/06/2008 A 2013


These satellites measure the height of the water. The radar signal transmitted by the satellite
is reflected by the surface. From round trip time the distance is calculated from the satellite
relative to the ocean. Then a station sends a laser for the satellite to determine its distance from
the station. It also receives signals from Doris marks. From these satellite calculates its distance
in relation to the center of the Earth. After making the difference between its distance in relation to
the center of the earth and the distance of the satellite in relation to the ocean we get the ocean height.

Click here to see an animation that explains how these satellites measure the sea level


During El Niño and La Niña (ENSO) in the Pacific and the North Atlantic Oscillation (NAO) weekly sea surface height anomalies were found from measurements of the satellite Topex-Poseidon.

Calculation of the shift in sea level in the North Atlantic (except seasonal
variations and turbulence) from the satellite Topex-Poseidon. The variation
of the NAO index (in red) during the same period is also shown.
(Credits Cnes)


It is thus that from Topex-Poseidon data from 1993 to 2000, it has been possible
to notice that the sea level dropped and flowed in different regions and not in the same way.

Click here to see a video (9.30 MB) of the variation of the SSH
(height of the sea surface) over 5 years from September 1992
to September 1997 from the Topex-Poseidon measurements

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