Ultra rapid oscillations in Earth rotation parameters derived from GNSS data

The purpose of this study is to investigate the potential of recent GNSS observations for determination of Earth rotation parameters (ERP) at short, down to subdaily, periods with the high precision currently achieved by this technique. The GPS is currently the most important technique to estimate the pole coordinates x, y and also provides the LOD estimates. Other GNSS measurements, such as those from GLONASS or Galileo, might be combined with GPS data to improve the precision of the parameter determination.

As currently only few observations of the Galileo system are yet available, we use here as input data the ERP based on GPS and GPS+GLONASS observations covering about 8 month in 2008 and 4 month in 2014. The GNSS solution is based on data from about 170 sites of the IGS network. For about 80 stable sites a NNR constraint to their ITRF2008 coordinates has been applied. Hourly ERPs were derived after applying all daily and sub-daily ERP-models provided by the IERS Conventions 2010. For the purpose of comparison we use also the 3-hourly atmospheric and oceanic angular momentum (AAM, OAM) data estimated by Schindelegger et al. (2016, submitted to Surveys in Geophysics).

We made spectral analysis of the derived ERP parameters and the excitation functions in the range of periods from 2 to 70 hours. The ERP parameters computed from two kinds of the GNSS observations are close but their differences are not negligible. Oscillations with periods of 8 and 12 hours are detected in the spectra of both GPS and GPS+GLONASS series of polar motion. Similar oscillations are also seen in the spectra of the polar motion excitation functions. This 8 hours oscillation is also apparent in the dUT1 series.

On top of this calculations we provide a rough estimate of the contribution of Galileo data (from the MGEX campaign resource) to the ERP estimation, based on simulated as well as real (but limited) observation data in 2015.