IDS contribution to the IERS ITRF2008 call for participation

(First iteration Feb. 2009)

(Last iteration Nov. 2009)
The IDS-3 SINEX time series may be downloaded at ftp://ftp.ids-doris.org/pub/ids/combinations/ITRF2008-IDS/IDS-3/

ITRF2008 Call

IDS Analysis

Two IDS Analysis Working Group meetings have been organized in March and June 2008 in Paris, Bureau des Longitudes, and an IDS workshop in Nice, 12-14 November 2008. Eight DORIS analysis centers participated including four official analysis centers (IGN; LCA ; GOP ; ESA), and four candidate analysis centers (NCL - University of Newcastle; GAU - Geoscience Australia; INA - Institute of Astronomy, Russian Academy of Sciences, and GSC - NASA Goddard Space Flight Center). All these centers are working to provide SINEX solutions for inclusion in the IDS combined solution that will be submitted to the IERS for ITRF2008.

This is an important step for IDS Analysis centers! Indeed for ITRF2005, only two individual DORIS solutions were included: IGN and LCA. A main goal was to improve the models and processing strategies of the new ACs, to discuss the standards and to get ready for the IDS contribution to ITRF2008.

The IDS Analysis Centers are listed hereafter. Analysis activities are coordinated by F. Lemoine.

The IDS combinations of weekly solutions for the station coordinates and the Earth Orientation Parameters are realized with CATREF, the IGN/LAREG Software.

Weekly SINEX series contributions

The following table summarizes the AC submissions and associated main models as well as the DORIS SINEX series provided for the contribution to ITRF2008.
See also the DORIS satellites constellation history status.

(1) var-cov: variance-covariance, NEQ: Normal Equation
(2) Specific recommendation for Jason-1 is to exclude Jason-1 data after 2003 because of the USO sensitivity to SAA (cf AWG-June 2008)

Compliancy with IERS Call

The delivered SINEX are not yet fully compliant with the IERS call for participation requirements. The non compliant items are the followings:

• 3 ACs (ina, ign, gau/gsc) provide UT1 in the set of EOPs for each day while the call only expects VLBI to provides UT1,
• lca AC applies atmospheric correction while it is requested NOT to correct for any geophysical fluid loading effects, except for tidal ocean loading.

Concerning the last issue, LCA will provide a new SINEX series for which the weekly mean value of the atmospheric loading correction is removed.

SINEX preprocessing

The preprocessing of the SINEX solutions is realized per AC series and includes the following steps:

• verification of DORIS station identification (dome #, mnemo)
• rejection of stations over the whole time period (never used),
• rejection of stations over specific periods (partially used),
• verification of solution number and discontinuities (breaks - to be consolidated before weekly combination by analysis of all AC stations times series -),
• when NEQ provided, inversion of free singular equations,
• projection using minimal constraints and rejection of perturbating stations,
• weekly comparison with ITRF2005 at epoch of each solution,
• analysis and rejection of high residual stations.

(to be completed)

Per week Combination

The weekly combination results from a 7-parameter transformation calculated every week using an IDS ITRF2005 datum . This datum results from a selection of DORIS stations having the best on position (< 1 cm) and velocity (< 2 mm/yr), and included in the week solution to be processed. For each week, the steps are as follows:

• datum generation with selection of common stations to all ACs SINEX and propagation at epoch of the solutions,
• first CATREF combination,
• residual analysis and station rejection (minimum number needed),
• weighting with variance factor,
• iteration process and final combined solution with TRF parameters.

Note that at least 3 solutions are needed to generate a weekly combined solution. That is to say that a combination is possible over the 1997.0-2008.8 period.

Combination results (under construction)