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Space Gradiometry on the Reference Ellipsoid
Lundi 22 avril 2013 à 14h00
Erik Grafarend
Space Gradiometry with respect to the International Ellipsoid is an integral part of Space Geodesy. Here we introduce the gravitation tensor (tidal tensor, curvature tensor) in terms of ellipsoid harmonics introduced by Jacobi (1834). We fit the model of Somigliani-Pizzetti reference field in Jacobi ellipsoidal/shpheroidal coordinates. It balances the conservative parts of the gravitational functionals of second order and the centrifugal functionals of second order as well. We study the central question of how many terms of an ellipsoidal harmonic setup by degree/order are estimable. As a result we find singularities caused by degree/order of type zero/zero, one/minus one, zero, plus one (datum problem/gauge problem). A speciality is our analysis in terms of tensor-valued ellipsoidal harmonics. The treatment extends previous results projects in terms of spherical harmonics world-wide in use to the extent that the trace of the gravity tensor is not zero due to the rotation of the Earth or any other rotating planet.
Bâtiment Condorcet, 3ème étage
Salle Luc Valentin (454A)
Deep clays and surface weathering: two types of alteration on Mars
Vendredi 1er mars 2013 - 11h00 à13h00
Bâtiment Condorcet
10, rue Alice Domon et Léonie 75013 Paris
Salle 454A Luc Valentin (anciennement Salle Paul Klee)
Damien LOIZEAU, Université Lyon 1
Résumé:
During the last decade, Martian Orbiters and Rover missions have provided new evidences of the ancient role of liquid water on Mars: we now have mineralogical detections to be added to the previous morphological observations. Liquid water is our most important tracer of a possible habitability of other planets and satellites.
One of the discoveries concerns the phyllosilicates (e.g. clay minerals) which form by alteration of other rocks, over extant period of time, in the presence of liquid water. They have been detected and mapped from orbit by Mars Express (ESA) and Mars Reconnaissance Orbiter (NASA), and are driving the selection of landing sites on Mars for the future rover missions (Mars Science Laboratory, ExoMars...). Following the detection of these hydrated minerals, we need to understand the geological and climatological context of their formation, to constrain when water was present, how much and for how long, and the chemical environment at that time. I have been studying clay-bearing outcrops on Mars with many different datasets from the last 4 Martian orbiters. I will describe two very different types of environments were clays-bearing units formed, from kilometer depth to surface weathering.
14 octobre 2011 à 11h : Séminaire "GPS Array as a Sensor of Lithosphere, Troposphere and Ionosphere"
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