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 Universität 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/.

The possibility of observing satellites with the very long baseline interferometry (VLBI) technique has been discussed for several years in the geodetic community, with observations of either existing satellites of the global navigation satellite systems or of satellites dedicated to realise a space tie. Such observations were carried out using the Australian telescopes in Hobart and Ceduna which, for the first time, integrated all the necessary steps: planning the observations (automated scheduling), correlation of the data and the generation of a series of time delay observables suitable for a subsequent geodetic analysis. We report on the development of new and the adaptation of existing routines for observing and data processing, focusing on technology development. The aim was to use methods that are routinely used in geodetic VLBI. A series of test experiments of up to six hours duration was performed, allowing to improve the observations from session to session and revealing new problems still to be solved. The newly developed procedures and programs now enable more observations. Further development assumed, this bears the prospect of being directly applied to the observation of dedicated space-tie satellites.

The possibility to observe satellites with the geodetic Very Long Baseline Interferometry (VLBI) technique is vividly discussed in the geodetic community, particularly with regard to future co-location satellite missions. The Chinese APOD-A nano satellite can be considered as a first prototype—suitable for practical observation tests—combining the techniques Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS) and VLBI on a single platform in a Low Earth Orbit (LEO). Unfortunately, it has hardly been observed by VLBI, so major studies towards actual frame ties could not be performed. The main reason for the lack of observations was that VLBI observations of satellites are non-standard, and suitable observing strategies were not in place for this mission. This work now presents the first serious attempt to observe the satellite with a VLBI network over multiple passes. We introduce a series of experiments with the AuScope geodetic VLBI array which were carried out in November 2016, and describe all steps integrated in the established process chain: the experiment design and observation planning, the antenna tracking and control scheme, correlation and derivation of baseline-delays, and the data analysis yielding delay residuals on the level of 10 ns. The developed procedure chain can now serve as reference for future experiments, hopefully enabling the global VLBI network to be prepared for the next co-location satellite mission.

The D-A-CH geoid project was initiated in 2017 between the national mapping agencies of Germany (BKG), Austria (BEV) and Switzerland (swisstopo), as well as the regional authorities of the German federal states of Bavaria (LDBV) and Baden-Württemberg (LGL), with the motivation to better harmonize the basis for height determination.In these countries, the official national height reference systems that are still in use apply different definitions of the height and the zero levels refer to different tide gauges and epochs. Additionally, the treatment of the permanent tide is not fully consistent. This causes differences at the decimeter scale which also vary along the national borders. At the same time, Austria and Switzerland do compute and store also EVRS-compatible geopotential numbers that are valuable for height system unification.The ambitions of the initiative therefore mirror the situation as described above ‒ to foster and to intensify the cooperation between the partners regarding regional gravity field modeling and to provide better information about the transformations between the national height systems.It was agreed that the cooperation should first focus on a case study area around Lake Constance, with envisaged extension to the complete territories of the “D-A-CH countries” and/or, ideally, to the most of the European Alps. The following achievements have been reached for the focus area:In view of these developments, and taking into account that these challenges are not unique for this specific area, it is planned to extend this initiative to the computation of the entire European Alps (and surrounding lowland areas) and rename the project to “European Alps Geoid (EAlpG)”.We believe that this project can contribute to a better understanding of height differences across borders. Such height differences are for instance of great interest for ground water level investigations or flood protection. Other crucial applications for cross-border height unification are engineering projects such as tunnels, bridges, supply lines, etc.What is more, these activities shall be embedded in a pan-European geoid initiative within EUREF. Contributing to the upcoming EUREF Working Group “European Height Reference Surface”, the European Alps Geoid will be one of many cornerstones to build an official EVRS height reference surface.Potential cooperation partners have been contacted. Nevertheless, the initiative shall be open to interested parties. A virtual meeting is planned to be held shortly after the vEGU2021.