Because GNSS (Global Navigation Satellite System) satellite orbits realize a quasi-inertial system, the analysis of tracking data from the global IGS (International GNSS Service) network allows the estimation of Earth rotation parameters (ERPs). As a result x and y positions of the Earth's rotation axis in an Earth-fixed frame (polar motion) and their rates as well as the excess length of day (LOD) values are obtained.
CODE computes ERPs with a 1-day resolution, represented as piece-wise linear parametrization. To deliver them in SINEX format to the IGS for combination, the representation of the parameters is transformed to offset and drift by applying some continuity conditions. Separate time series are provided directly to the IERS (International Earth Rotation and Reference Systems Service) for analysis. Today a time series of more than 13.5 years, covering more than 11.5 Chandler periods, is available from CODE. The Figures show the Chandler wobble of the Earth's rotation axis starting in June 1993. The accuracy of the daily values is of the order at 0.1 mas.
Last update of the plots: 18-Jan-2020
Since January 1995 CODE is internally using a 2-hours resolution for polar motion and LOD parameters, extending the unique high resolution time series to more than 12 years. Since April 1994 also daily values for drifts in nutation in longitude and obliquity are estimated at CODE. These particular time series covers more than 13 years by now.
CODE is processing global GPS and GLONASS tracking data in a fully combined analysis since June 2003. Due to the different orbital characteristics of GLONASS with respect to GPS - the orbital period is 11:16 instead of 11:58 hours - a slight improvement of estimated pole parameters may be expected. Due to the small number of GLONASS satellites and, in particular, the sparse global GLONASS-tracking network, it was not possible to see a clear improvement of the ERP series.