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Earth's Rotation

Parameters of the Earth’s Orientation Determined by the Combination of GINS-DYNAMO at the Observatoire de Paris

Project Managers : Jean-Yves Richard / Christian Bizouard
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Using the multi-technique combination created by the GRGS in 2000, the Observatoire de Paris/SYRTE team is responsible for the inversion of normal equations provided by each intra-technical center (GPS: CNES / CLS; VLBI: Observatoire de Bordeaux; SLR: Géoazur; DORIS: CNES / CLS) to determine the orientation parameters of the Earth, the coordinates of ground stations, and additionally parameters of the troposphere and the positions of quasars in the celestial frame. These intra-technical centers develop normal equations using the same software (GINS) and the same models or a priori assumptions. The inversion is performed using the DYNAMO software. Coherence between Earth’s rotation and reference frames is thus assured.

The joint processing of all the astro-geodetic observations by the GINS application thus avoids the pitfall of using inhomogeneous models or a priori assumptions. The combination of normal equations and their inversion by DYNAMO allows us to determine geodetic parameters both more frequently (e.g. every 3 hours for polar motion) and in principle more accurately.

This activity, begun in 2008, is growing rapidly: the procedures are currently in a test phase, in partnership with international centers (GFZ / ESOC / DGFI / AIUB / MAO).

The Department of Earth Rotation of the Observatoire de Paris evaluates the parameters of the Earth’s orientation that result from this inversion. Here are its conclusions about the state of the project:

Polar motion:a great many solutions have been made by adopting various strategies. While the variations of a few days concur with those of conventional solutions, the diurnal and sub-diurnal variations should be used with caution.

Nutations: VLBI observations supplemented by those from GPS enable us to determine nutations with a greater rate, at the level of a day, instead of 5 or 7 days. This allows us to explore the frequency band between 2 and 7 days. However, the fluctuations obtained have not been validated.

UT1: problematic solutions displaying strong deviations.

Coordinates of the Pole (x,y) every 6 hours (at 0h, 6h, 12h, 18h)

Differences in the celestial pole every 12 hours (at 0h and 12h)