[Paper Review] VLBI analyses with the GINS software for multi-technique combination at the observation level

G. Bourda, P. Charlot+1 more|ArXiv.org|Mar 10, 2008

GNSS positioning and interference2 references3 citations

TL;DR

This paper presents VLBI data analyses using the GINS software for multi-technique geodetic combination at the observation level, demonstrating that GINS produces Earth Orientation Parameter (EOP) solutions with sub-milliarcsecond agreement (0.2 mas) against the IVS Analysis Coordinator's combined results. The study confirms GINS's capability to deliver high-precision, consistent EOP estimates comparable to other leading VLBI analysis centers, supporting its role in global geodetic reference frame and Earth system monitoring.

ABSTRACT

A rigorous approach to simultaneously determine a Terrestrial Reference Frame (TRF) and Earth Orientation Parameters (EOP) is now currently applied on a routine basis in a coordinated project within the Groupe de Recherches de Géodésie Spatiale (GRGS) in France. Observations of the various space geodetic techniques (VLBI, SLR, LLR, DORIS and GPS) are separately processed by different analysis centers with the software package GINS-DYNAMO, developed and maintained at the GRGS/CNES (Toulouse). This project is aimed at facilitating fine geophysical analyses of the global Earth system (GGOS project). In this framework, Bordeaux Observatory is in charge of the VLBI (Very Long Baseline Interferometry) analyses with GINS for combination with the data of the other space geodetic techniques at the observation level. In this paper, we present (i) the analyses undertaken with this new VLBI software, and (ii) the results obtained for the EOP from beginning 2005 until 2007. Finally, we compare this EOP solution with the IVS (International VLBI Service) Analysis Coordinator combined results. The agreement is at the 0.2 mas level, comparable to that of the other IVS Analysis Centers, which demonstrates the VLBI capability of the GINS software.

Motivation & Objective

• To evaluate the performance of the GINS software in processing VLBI observations for multi-technique geodetic combination at the observation level.
• To assess the accuracy of EOP solutions derived from GINS-processed VLBI data against the IVS Analysis Coordinator's combined EOP series.
• To validate GINS as a reliable tool for routine VLBI analysis within the coordinated multi-technique geodetic framework of the GGOS project.
• To support the integration of VLBI data into a unified, homogeneous solution across all space geodetic techniques (GPS, SLR, DORIS, LLR, VLBI).

Proposed method

• VLBI data from IVS intensive, R1, and R4 sessions (2005–2007) were processed with GINS using a fixed VTRF2005 terrestrial reference frame and ICRF celestial reference frame.
• EOP parameters (Xp, Yp, UT1-UTC, dψ, dε) were estimated weekly, along with station coordinates, clock corrections, and zenith tropospheric delays.
• Clock and tropospheric delays were modeled using piecewise continuous linear functions with 2-hour and 1-hour breaks, respectively, and continuity constraints of 10 μs and 10 cm.
• Tidal, atmospheric loading, and mapping models (IERS Conventions 2003, FES2004, 6h-ECMWF, Niell) were applied to improve modeling accuracy.
• Weekly normal equation matrices from VLBI were combined with those from GPS, SLR, LLR, and DORIS at the observation level to produce a unified solution.
• Comparisons were made between GINS-derived EOPs and the IVS combined EOP series (ivs06q3e.eops), using non-weighted RMS to assess differences.

Experimental results

Research questions

• RQ1 How accurately does the GINS software reproduce Earth Orientation Parameters (EOP) from VLBI observations compared to the IVS Analysis Coordinator’s combined solution?
• RQ2 What is the level of agreement between EOP solutions derived from GINS and the IVS combined EOP series in terms of RMS differences?
• RQ3 To what extent does the use of VTRF2005 instead of ITRF2000 affect the EOP solution consistency with the IVS combined series?
• RQ4 Can GINS produce EOP solutions with precision comparable to other established IVS analysis centers?
• RQ5 What are the residual delay errors in GINS-processed VLBI data, and how do they vary across different session types?

Key findings

• The GINS software produced VLBI-only EOP solutions that agree with the IVS Analysis Coordinator’s combined EOP series at the 0.20 mas level for polar motion coordinates.
• The agreement for celestial pole offsets (dψ sinε and dε) was 0.15 mas, demonstrating high consistency in Earth rotation and orientation parameters.
• The difference in UT1-UTC was 10 μs, indicating high accuracy in Earth's rotation angle estimation.
• Post-fit weighted RMS delay residuals averaged 1.08 cm (36 ps) for IVS-R1 sessions and 0.97 cm (32 ps) for IVS-R4 sessions, indicating good data fit.
• The mean differences between GINS and IVS EOP series were small, with RMS values of 212 μas for Xp and 211 μas for Yp, confirming high solution stability.
• The results demonstrate that GINS is capable of producing EOP solutions of comparable quality to other leading IVS analysis centers, validating its use in multi-technique geodetic combination.