- All available sessions from 1984 until the present are used, and the solution is updated every three months.
- The combination is based on 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 every three months.
- Two combined series are available:
Combined series (dX, dY):
The nutation offsets are dX and dY, referring to the IAU2006 precession-nutation model, excluding free core nutation
- Combined series (dPsi, dEps):
The nutation offsets are dPsi and dEps, referring to the IAU2000A precession-nutation model, excluding free core nutation
- Matrices are transformed to the mean epoch of all contributions by using the respective earth orientation parameter rates, before accumulating the individual normal equation matrices.
- The individual normal equation matrices are then transformed into 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 then accumulated.
- Earth orientation parameters are estimated by fixing all station components to their ITRF2008 values.
Finally, two types of comparisons are carried out for the purpose of quality control:
- 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 ensure comparable results, the calculations of bias, WRMS, and RMS were carried out only for those sessions that were analyzed by every Analysis Center.