Current Status of the EU-VGOS Project

The EU-VGOS project began in 2018 with\ua0the aim of using the VGOS infrastructure in Europe\ua0to investigate methods for VGOS data processing. The\ua0project is now structured into Working Groups dealing\ua0with operations (stations), e-transfer, correlation and\ua0post-processing, and analysis. This is a report on the\ua0status of the project

Beobachtung von atmosphärischen Gezeiten in den Erdrotationsparametern mit der VLBI

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersThe Earth's body is enveloped with fluids represented mostly by the atmosphere and oceans, which force the Earth's rotation vector to alter. On daily and sub-daily time scales, differential gravitational forces of the Moon and Sun govern the regular Earth rotation variations by raising ocean tides. A distinct addition and modulation of these ocean tide effects is provided by atmospheric tides, which result from cyclic absorption of insolation at upper air and boundary layer heating at the Earth's surface. Short period tidal mass variations that are of particular relevance to Earth rotation are those with Sun-locked diurnal S_1 (24 hour) and semidiurnal S_2 (12 hour) periodicities. Atmospheric tides were discovered first in the variations of the surface pressure field, whose measurements are ingested into weather models along with a presentation of the S_1 and S_2 cycles from remote sensing. The impact of these variations on Earth rotation can be determined from a geophysical modeling perspective by means of an angular momentum approach. In this thesis, the Earth's rotation effects related to atmospheric tides are evaluated in a separate approach based on the (vlbi) observations. Elucidating the potential reasons for the well-known discrepancies in Earth rotation between these two approaches formulates the core argumentation in this thesis. Overall, atmospheric tide effects in Earth rotation are detected on the expected level in the analysis of the (vlbi) observations. The reliability of these signals is confirmed directly through a comparison with geophysical estimates and indirectly validating the obtained high-frequency ocean tide terms against the range of reference solutions. For polar motion, previous studies have documented a significant discrepancy between the geodetic and geophysically derived S_1 terms at the order of 10 µas or large. This difference is mitigated to 5 µas in the present study, yet this value is above the best threefold formal error level in polar motion (2.5 µas) provided by the undertaken (vlbi) analysis. In a supplementary study Earth rotation tide models were considered in dependence on the applied corrections to the station (vlbi) positions due to the loading effects of the fluids as provided by different geophysical models and vice versa. However in both approaches, the parameter estimates based on different geophysical models demonstrate statistically insignificant variations under threefold formal error level.14

Vienna Vlbi And Satellite Software (Vievs) For Geodesy And Astrometry

The Vienna VLBI and Satellite Software (VieVS) is state-of-the-art Very Long Baseline Interferometry (VLBI) analysis software for geodesy and astrometry. VieVS has been developed at Technische Universitat Wien (TU Wien) since 2008, where it is used for research purposes and for teaching space geodetic techniques. In the past decade, it has been successfully applied on Very Long Baseline Interferometry (VLBI) observations for the determination of celestial and terrestrial reference frames as well as for the estimation of celestial pole offsets, universal Time (UT1-UTC), and polar motion based on least-squares adjustment. Furthermore, VieVS is equipped with tools for scheduling and simulating VLBI observations to extragalactic radio sources as well as to satellites and spacecraft, features which proved to be very useful for a variety of applications. VieVS is now available as version 3.0 and we do provide the software to all interested persons and institutions. A wiki with more information about VieVS is available at http://vievswiki.geo.tuwien.ac.at/.WoSScopu

Geodetic data analysis of VGOS experiments

Very Long Baseline Interferometry (VLBI) serves as one of the common geodetic methods to define the global reference frames and monitor Earth\u27s orientation variations. The technical upgrade of the VLBI method known as the VLBI Global Observing System (VGOS) includes a critical re-design of the observed frequencies from the dual band mode (S and X band, i.e. 2 GHz and 8 GHz) to observations in a broadband (2-14 GHz). Since 2019 the first VGOS experiments are available for the geodetic analysis in free access at the International VLBI service for Geodesy and Astrometry (IVS). Also regional-only subnetworks such as European VLBI stations have succeeded already in VGOS mode. Based on these brand-new observations we review the current geodetic data analysis workflow to build a bridge between geodetic observed delays derived from different bands