Input data

Space geodesy solutions. The used time series of solutions of space geodesy are summarized in the following table, indicating for each one, the time span and the type of constraints.

IDS-LCA solution

L. Soudarin (CLS)
J.F. Crétaux (LEGOS-GRGS)

A series of weekly station coordinates and daily pole coordinates has been computed using 13 years (January 1993 to December 2005) of DORIS measurements collected by the instruments onboard SPOT2, SPOT3, SPOT4, SPOT5, TOPEX/Poseidon and ENVISAT. The tracking data are processed nominally on 3.5-day arc (half a week of the GPS calendar) for all the 6 satellites using the GINS/DYNAMO software of the GRGS. Individual normal equations are accumulated to form weekly combined matrices. The inversion of these matrices yields the weekly solutions for the geodetic parameters. This time series of site and pole coordinates is expressed in free network with loose constraints (10 meter and 500 mas respectively). The coordinate solutions are expressed at the median epoch of the week. Pole coordinates are estimated daily at 12:00. The gravity field model used in the orbit computation is GRIM5-C1.

Computation strategy

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The strategy adopted for the ITRF2005 generation consists in the following steps, illustrated in $\fig1$:

• Apply minimum constraints equally to all loosely constrained solutions: this is the case of SLR and DORIS solutions
• Apply No-Net-Translation and No-Net-Rotation condition to IVS solutions provided under the form of Normal Equation
• Use as they are minimally constrained solutions: this is the case of IGS weekly solutions
• Form per-technique combinations (TRF + EOP), by rigorously staking the time series, solving for station positions, velocities, EOPs and 7 transformation parameters for each weekly (daily in case of VLBI) solution w.r.t the per-technique cumulative solution.
• Identify and reject/de-weight outliers and properly handle discontinuities using piece-wise approach. The discontinuity files used for each one of the 4 techniques are found here.
• Combine if necessary cumulative solutions of a given technique into a unique solution: this is the case of the two DORIS solutions.
• Combine the per-technique combinations adding local ties in co-location sites.

This final step yields the final ITRF2005 solution comprising station positions, velocities and EOPs. Note that EOPs start in the early eighties with VLBI, SLR and DORIS contribution starts on 1993 and GPS on 1999.5. The quality of the early VLBI EOPs is not as good as the combined EOPs starting on 1993.