Doris sees the seasons weighing on the Earth

Image of the month - May 2000

Amplitude of vertical crustal motions derived from models and observations of variations in atmospheric pressure, snow cover, soil moisture, and ocean mass distribution. (Credits Legos)
Comparison between vertical crustal motions derived from cumulative observation and model data (red) and from direct observations by the Doris system (blue) near two stations in the Doris network (Metsahovi, Finland, and Tristan da Cunha, South Atlantic). (Credits Legos)


Pressures on the Earth's surface cause it to move it out of shape in much the same way as a ball does when pressed. Pressures are exerted by the weight of the atmosphere and by snow cover, soil moisture, ocean water masses, and other forces. The Doris precise orbit determination and positioning system detects the resulting small crustal motions of no more than a few millimeters. In particular, it enables us to observe seasonal variations, due for example to snow (Metsahovi) or ocean water masses (Tristan da Cunha).

Doris is one of three orbit determination systems on the Topex/Poseidon satellite, and will fly on Jason-1 and Envisat in the near future. It is also onboard the Spot Earth observation satellites (Spot 2 and 4, and soon on Spot 5). The Doris system is a valuable tool for altimetry, its extreme accuracy making it possible to observe small-amplitude ocean phenomena, and for geophysics applications, where it allows us to detect even the tiniest motions of the Earth.

For further information :

Mangiarotti, S., A. Cazenave, L. Soudarin, J.-F. Cretaux, 2000: Annual vertical crustal motions predicted from surface mass redistribution and observed by space geodesy, J. Geophys. Res. (submitted).


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