DORIS and the Determination of the Earth's Polar Motion

International audienceDORIS (Détermination d'Orbite et Radiopositionnement Intégrés par Satellite) is a system used for precise orbit determination (POD) and ground-station positioning. It has been implemented on-board various satellites: the SPOT (Système pour l'Observation de la Terre) remote sensing satellites SPOT-2, SPOT-3, SPOT-4, SPOT-5, TOPEX/Poseidon and more recently on its successors Jason-1 and ENVISAT. DORIS is also a terrestrial positioning system that has found many applications in geophysics and geodesy; in particular, it contributes to the realization of the International Terrestrial Reference Frame, ITRF2000 and the forthcoming ITRF2005. Although not its primary objective, DORIS can bring information on Earth orientation monitoring, mainly polar motion and length of day (LOD) variations that complement other astrogeodetic techniques. In this paper, we have analyzed various recent polar motion solutions derived from independent analysis centers using different software packages and applying various analysis strategies. Comparisons of these solutions to the International Earth Rotation and Reference Systems Service (IERS) C04 solution are performed. Depending on the solutions, the accuracy of DORIS polar components are in the range of 0.5 1 mas corresponding to a few centimeters on the Earth's surface. This is approximately ten times larger than results derived from GPS, which are typically 0.06 mas in both components. This does not allow DORIS results to be taken into account in the IERS EOP combinations. A gain in the precision could come from technical improvements to the DORIS system, in addition to improvement of the orbit, tropospheric, ionospheric and Earth gravity field modeling

Monitoring Earth orientation using space-geodetic techniques: state-of-the-art and prospective

International audienceEarth orientation parameters (EOPs) provide the transformation between the International Terrestrial Reference Frame (ITRF) and the International Celestial Reference Frame (ICRF). The different EOP series computed at the Earth Orientation Centre at the Paris Observatory are obtained from the combination of individual EOP series derived from the various space-geodetic techniques. These individual EOP series contain systematic errors, generally limited to biases and drifts, which introduce inconsistencies between EOPs and the terrestrial and celestial frames. The objectives of this paper are first to present the various combined EOP solutions made available at the EOP Centre for the different users, and second to present analyses concerning the long-term consistency of the EOP system with respect to both terrestrial and celestial reference frames. It appears that the present accuracy in the EOP combined IERS C04 series, which is at the level of 200 muas for pole components and 20 mus for UT1, does not match its internal precision, respectively 100 muas and 5 mus, because of propagation errors in the realization of the two reference frames. Rigorous combination methods based on a simultaneous estimation of station coordinates and EOPs, which are now being implemented within the International Earth Rotation Service (IERS), are likely to solve this problem in the future

Apport des techniques spatiales à l'évaluation des paramètres de la rotation de la Terre

not availableJusqu’aux alentours de 1970, seule 1'astrométrie utilisant les observations d'étoiles permettait d’évaluer les paramètres de la rotation terrestre. Quelques années plus tard, de nouvelles techniques fondées sur l'observation de radio-sources extragalactiques par interférométrie, de satellites naturels (Lune) ou artificiels par télémétrie laser ou par effet Doppler se sont développées; elles ont montré rapidement leur aptitude à déterminer les coordonnées du pôle avec des précisions équivalentes au début et très supérieures actuellement à celles de 1'astrométrie. A partir des solutions obtenues par ces diverses techniques, le BIH calcule une série pondérée des paramètres de la rotation de la Terre. A l'heure actuelle, pour le mouvement du pôle, les poids des techniques spatiales dans la solution combinée du BIH sont devenus prépondérants (plus de 90 % pour les deux composantes)

Evolution of consistencies between EOP series and international reference

International audienc

The IERS combined solution C04: recent improvements

International audienc

Earth rotation monitoring, UT1 determination and prediction

International audienceMonitoring the Earth's rotation angle is essential in various domains linked to reference systems such as space navigation, precise orbit determinations of artificial Earth satellites including the Global Navigation Satellite Systems (GNSS), positional astronomy and for geophysical studies on time scales ranging from a few hours to decades

Prediction of UT1 and LOD Variations

International audienc

Prediction of UT1 and LOD Variations

International audienc

Monitoring UT1 using both VLBI and GPS estimates

International audienc