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  Descartes prizes

Aims and Objectives of the Descartes Prizes

The Descartes Prizes are among the activities supported under the European Commission's Seventh Framework Programme, within the Research Directorate Science and Society.

Communication prize

  • Pinpoint positioning in a wobbly world

  • Throughout society, there is a growing demand for precise positioning and navigation systems - to improve the efficiency of travel, enhance personal security and increase the reliability of geophysical measurements. The Royal Observatory of Belgium in collaboration with groups from eight European countries has successfully produced a highly accurate reference framework, using detailed computation of variations in the Earth's rotation in space.

    The rotation of the Earth has long been used as a measure of time, and the stars as reference points to determine travellers' whereabouts on the globe. Today, inexpensive global positioning systems receive data sent by orbiting satellites, which are then processed by unmoving terrestrial receiving stations, and can pinpoint the location of a person or vehicle to within just a few metres.

    Research done by the international teams resulted in the development of an improved global positioning reference framework with an unprecedented accuracy - from 2 metres to within 2-3 centimetres. Positioning is determined using two reference frames: the terrestrial frame, fixed in relation to the Earth's crust and rotating synchronously with the planet; and the celestial frame, which is immobile in space. The relationship between these frames is complicated by the fact that the rotation and orientation of the Earth is subject to irregularities caused by the gravitational pull of the sun and moon, as well as by many other factors that are progressively being identified by geodesists. Because the Earth is an ellipsoid flattened at its poles, the combined forces acting upon it produce changes in both the speed of rotation and the orientation of the axis of spin. The term 'precession' describes the long-term trend of this latter motion, while 'nutation' is the name given to shorter-term periodic variations, which were the prime focus of the present project.

    Nutation and precession are measured using very long baseline interferometry (VLBI), a technique that employs huge radiotelescopes to observe extra-galactic quasars. The researchers noted significant differences between the VLBI observations and the results obtained from applying a theoretical model adopted by the International Astronomical Union (IAU) in 1980, based on the idea that Earth acts as a deformable object. However, the Earth is a complex object and the aim of a working group, established in 1996 and chaired by Prof. Dehant, was to come up with a new model relating nutation and precession to the sophisticated concept of a non-rigid Earth with a solid inner core, a liquid outer core, a deformable convective mantle, an atmosphere, and oceans. The study required collaboration between specialists in celestial mechanics, geophysics, atmospheric and ocean dynamics and astronomy. By 2000, the group had converged toward an improved nutation model, which was presented for adoption by the IAU in 2000 and by the International Union of Geodesy and Geophysics (IUGG) in July this year. The International Earth Rotation and Reference Systems Service (IERS) is now implementing the model in all geodetic techniques.

    The researchers made giant strides in understanding and modelling the physical processes associated with nutation. For example, the old model could compute the amplitude of nutations with an accuracy of around 2 metres. The team have now reduced the error to just 2-3 centimetres, which had never previously been achieved. This will be extremely helpful to European and international satellite missions. At the same time, it allows scientists to learn much more about the interior of the Earth and its magnetic field, which are not directly observable from the surface.

    As a next step, the group plans to apply the same methodology to a study of the planet Mars, in order to determine whether this also has a liquid core. The experiments are part of a network science mission, due in 2009, which aims to deploy four geophysical and meteorological stations on Mars.

    Contact:

    Prof. Veronique Dehant of the Royal Observatory of Belgium in association with researchers from her institution and from the Bureau International des Poids et Mesures in Sevres, Institut de Mécanique Céleste et de Calcul des Ephémérides in Paris and the Observatory of Paris (France), the Space Research Centre of the Polish Academy of Sciences in Warsaw (Poland), Complutense University of Madrid, the Universities of Alicante and Valladolid (Spain), Technical Universities of Dresden and Munich and GeoForschungsZentrum Potsdam (Germany), the Technical University of Vienna (Austria), Astronomical Institute of the Academy of Sciences of Czech Republic in Prague (Czech Republic), the Main Astronomical Observatory of the National Academy of Sciences of Ukraine in Kiev (Ukraine) and the Sternberg State Astronomical Institute of Moscow State University (Russia).

    Website: http://www.astro.oma.be


Descartes Prizes:    2005  2004  2003  2002  2001  2000