IDS contribution to ITRF2008

The International DORIS Service (IDS), in operation since 2003, submitted three sets of solutions to ITRF2005 from the IGN/JPL, LEGOS/CLS, and INASAN analysis centers, but no DORIS technique combination. Since that time new analysis centers have become operational including the Geodetic Observatory Pecny (GOP), the European Space Operations Center (ESOC), Geoscience Australia (GAU), the NASA Goddard Space Flight Center (GSC), and the University of Newcastle (NCL). These analysis centers run different software, including Gypsy (IGN & INASAN), GINS (LCA), Bernese (GOP), NAPEOS (ESOC), GEODYN (Geoscience Australia and NASA GSFC) and FAUST (NCL). In order to contribute to ITRF2008, seven analysis centers processed DORIS data from TOPEX/Poseidon, SPOT2, SPOT3, SPOT4, SPOT5, and ENVISAT from 1992 to 2008, producing weekly SINEX solutions or normal equations. The weekly SINEX files from seven AC’s were processed with the CATREF software. Three iterations of an IDS weekly combined time series were completed. The IDS-1, and IDS-2 combinations were preliminary station-only solutions. In the final combination, IDS-3, both stations and the Earth Orientation Paramters (EOP’s) were adjusted. Between each of the IDS combinations, the combination strategy (station filtering, outliers, weighting, scale or geocenter contributions) was improved and the AC’s SINEX series were refined. Some series were extended in data span while others were recomputed to correct anomalies or to improve the quality of the submissions, based on feedback from the combination analyses and intercenter comparisons. For example in IDS-1, both the GAU and GSC solutions were affected by a 20 mm scale offset that was removed in IDS-2 and IDS-3 after the application of improved troposphere modelling in the GEODYN software. The analysis for IDS-1 showed a higher station position WRMS in the vicinity of the high solar flux periods (late 2001-2002). Consequently for IDS-2, several AC’s (LCA, GAU, GSC) recomputed their orbits to estimate drag coefficients more frequently to mitigate this effect. The analysis of the frequency and amplitude of geocenter and scale signals was used to define the AC contributions to geocenter and scale in the final combination IDS-3. The comparisons of IDS-3 w.r.t. ITRF2008 are presented. Future prospects and plans for the IDS DORIS analyses are discussed.