- All available sessions from 1984 up to now have been used.
- The solution is updated every three months.
- The combination is based on the approach of addition of normal equation matrices and makes use of datum-free normal equation matrices of VLBI sessions which are provided as SINEX files.
- The combined earth orientation parameter series will be updated all three month.
- Two combined series are available:
- Combined series (dX, dY):
The nutation offsets are dX, dY referred to IAU2006 precession-nutation model excluding free core nutation
- Combined series (dPsi, dEps):
The nutation offsets are dPsi, dEps referred to IAU2000A precession-nutation model excluding free core nutation
- Before accumulating the individual normal equation matrices the matrices are transformed to the mean epoch of all contributions by using the respective earth orientation parameter rates.
- Furthermore the individual normal equation matrices have to be transformed to a common set of apriori values for station coordinates and earth orientation parameters.
- Weighting factors determined by variance component estimation are applied to the normal equation systems.
- The datum-free normal equation matrices are accumulated.
- Earth orientataion parameters are estimated by fixing all station components to their ITRF2008 values.
- To perform a quality check comparisons are carried out
- internal comparisons of the individual solutions with respect to the combined solution,
- external comparisons with the earth orientation parameters of the IGS Final Combined Solution (igs00p03.erp) as well as with the IERS C04 (eopc04.62-now) earth orientation parameter series.
Notice: To get comparable results, the calculations of bias, WRMS and RMS were carried out only for those sessions that were analysed by every analysis center.