Acta Geodyn. Geomater., Vol. 16, No. 1 (193), 85–97, 2019 DOI: 10.13168/AGG.2019.0007 journal homepage: https://www.irsm.cas.cz/acta ORIGINAL PAPER ON THE ASSESSMENT OF THE TEMPORAL EVOLUTION OF GLOBAL TERRESSTRIAL REFERENCE FRAMES: THE VEDA APPROACH Dimitrios AMPATZIDIS BKG German Federal Agency for Cartography and Geodesy, Richard Strauss Allee 11, 60598 Frankfurt a.M. Germany Corresponding author‘s e-mail: Dimitrios.Ampatzidis@bkg.bund.de ABSTRACT In this paper, we describe an alternative methodology for the assessment of global Terrestrial Reference Frames (TRFs), called the Velocity Decomposition Analysis (VEDA). Although it is related to the well-known Helmert transformation, a new conceptual manner is presented and discussed. All the necessary mathematical formulas for the adjustment and the quality assessment are provided, as well as a discussion of the similarities and differences to the existing approaches. The core of the VEDA concept lays on the separation of the velocities in two parts: the transformation related one and the optimal velocities, respectively. Using the suggested strategy, we test the global TRFs, the ITRF2008 and the DTRF2008. Their comparison in terms of Helmert transformation parameters reveals discrepancies reaching 0.83 mm/yr for the orientation rates, 0.97 mm/yr for the translation rates and 0.32 mm/yr for the scale rate. The comparison between the new approach and the classical Helmert transformation shows a consistency at the level of 0.66 mm/yr in a mean sense. In addition, we find a relative bias between the two frames reaching 0.44 mm/yr. The new approach also allows quantifying the geometric effect which corresponds to the impact of the systematic inconsistencies and the effect of the set of stations global distribution. ARTICLE INFO Article history: Received 11 September 2018 Accepted 28 January 2019 Available online 15 February 2019 Keywords: Terrestrial reference frame Helmert transformation Reference frame assessment Geometric effect ITRF2008 DTRF2008 the combination of the geometric space geodetic techniques: Doppler Orbitography and Radio- positioning Integrated by Satellite (DORIS), Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI); see e.g., Altamimi et al. (2002). Concerning the accuracy assessment, different possibilities for TRF validation exist. In general, they can be separated into internal and external validation (see Collilieux et al., 2013). The internal validation is implemented through the comparison of the combined solution to each of the technique-wise TRFs. For instance, the ITRF origin consistency is assessed through its comparison with the SLR-based TRF (e.g. Dong and Fang, 2007; Altamimi et al., 2008). The origin is realized from SLR-only with an accuracy of 10 mm over the time-span of the SLR observations (Altamimi et al., 2011). The global TRF scale consistency can be assessed with the comparison to the VLBI and the SLR based TRFs (Altamimi et al., 2008) since the ITRF2008 scale and its rate agree with the associated scale of VLBI and SLR at the level of 1.05 ppb and 0.05 ppb/yr, respectively (Altamimi et al., 2011). The orientation and its rate are defined through constraining the new ITRF solution having 1. INTRODUCTION Global Terrestrial Reference Frames (TRFs) play a prominent role in precise 4D point determination. Highly accurate and stable TRFs are an indispensable prerequisite for a correct interpretation of geodetic products describing the geometry, the gravity field, and the rotation of the Earth, especially in the framework of the Global Geodetic Observing System (Beutler et al., 2009). The most recent International Terrestrial Reference Frame (ITRF), adopted by the International Earth Rotation and Reference Systems Service (Petit and Luzum, 2010), is the ITRF2014 released on January of 2016 (Altamimi et al., 2016). The previous solution was the ITRF2008 (Altamimi et al., 2011) provided by the National Institute of Geographic and Forest Information (IGN). Alternatively, the DTRF2008 (Seitz et al., 2012) as a realization provided by the German Geodetic Research Institute of the Technical University of Munich (DGFI-TUM) as another official Combination Centre of the (International Earth Rotation and Reference Systems Service, IERS) is available. Another recent realization of a global reference frame is the JTRF2014, provided by the Jet Propulsion Laboratory (JPL, Wu et al., 2015). In general, the ITRFs provided within the last 20 years are based on Cite this article as: Ampatzidis D: On the assessment of the temporal evolution of global terrestrial reference frames: the VEDA approach. Acta Geodyn. Geomater., 15, No. 1 (193), 85–97, 2019. DOI: 10.13168/AGG.2019.0007