In this work, we present a status update and results of the designated research and development VLBI Intensive program VGOS-INT-S, observed between MACGO12M and WETTZ13S for the rapid determination of the Earth's phase of rotation, expressed via UT1-UTC. The main novelty of these sessions is the use of a special observation strategy, rapidly alternating between high- and low-elevation scans, enabling an improved determination of delays caused by the neutral atmosphere. Since 2021, 25 Intensive sessions have been observed successfully. In early 2022, VGOS-INT-S was among the most accurate Intensive programs with an average formal error σ_UT1-UTC of 3.1 μs and a bias w.r.t. IERS C04 of 1.1 μs. Later, the session performance decreased due to multiple technical difficulties.

We report the results of position ties for short baselines at eight geodetic sites based on phase delays that are extracted from global geodetic very‐long‐baseline interferometry (VLBI) observations rather than dedicated short‐baseline experiments. An analysis of phase delay observables at X band from two antennas at the Geodetic Observatory Wettzell, Germany, extracted from 107 global 24‐hr VLBI sessions since 2019 yields weighted root‐mean‐square scatters about the mean baseline vector of 0.3, 0.3, and 0.8 mm in the east, north, and up directions, respectively. Position ties are also obtained for other short baselines between legacy antennas and nearby, newly built antennas. They are critical for maintaining a consistent continuation of the realization of the terrestrial reference frame, especially when including the new VGOS network. The phase delays of the baseline WETTZ13N – WETTZELL enable an investigation of sources of error at the sub‐millimeter level. We found that a systematic variation of larger than 1 mm can be introduced to the Up estimates of this baseline vector when atmospheric delays were estimated. Although the sub‐millimeter repeatability has been achieved for the baseline vector WETTZ13N – WETTZELL , we conclude that long term monitoring should be conducted for more short baselines to assess the instrumental effects, in particular the systematic differences between phase delays and group delays, and to find common solutions for reducing them. This will be an important step toward the goal of global geodesy at the 1 mm level.

<p>The rapid determination of the Earth's phase of rotation, expressed through the Earth rotation parameter dUT1, is one of the core tasks of geodetic Very Long Baseline Interferometry (VLBI). To ensure a low latency between observation and analysis results, dedicated 1-hour-long VLBI sessions, so-called Intensives, are regularly observed. Two of these Intensive programs, namely INT2 and INT3, are organized and monitored by the joint IVS operation center DACH. </p><p>Within this study, a detailed overview over the last five years of the VLBI Intensive observing programs INT2 and INT3 is provided. INT2 sessions are typically observed on Saturdays and Sundays using a single baseline and a recording rate of 256 Mbps. INT3 sessions are multi-baseline Intensives with up to five stations, observed on Mondays with a recording rate of 1 Gbps. </p><p>Starting in 2019, the scheduling strategy of the INT3 sessions was significantly changed, leading to a reduction of the estimated average dUT1 formal errors by 25% (from (6.1 ± 2.0) µs to (4.5 ± 1.0) µs) for the 4-station network. The improvement w.r.t. dUT1 mean formal errors for the 5-station network is 45% (from (6.3 ± 1.7) µs to (3.5 ± 0.5) µs). </p><p>The best performing INT2 baseline is observed between station MK-VLBA (USA) and WETTZELL (Germany). Mid-2020, the same change was applied for these INT2 sessions, leading to a reduction in the average dUT1 mean formal error of 44% (from (11.7 ± 5.7) µs to (6.6± 4.7) µs). </p><p>Furthermore, comparisons of dUT1 estimates from various analysis centers w.r.t. IERS EOP C04 and JPL EOP2 are conducted. It is revealed that the previously mentioned INT2 baseline shows a bias of only -2.5 µs and 1.9 µs based on the estimates provided by the analysis centers Goddard Space Flight Center (GSF) and Bundesamt für Karthographie und Geodäsie (BKG), respectively, when compared with JPL EOP2. In contrast, the bias is 10.4 µs and 14.9 µs w.r.t. IERS EOP C04. </p><p>Besides analyzing dUT1 formal errors, the latency of the dUT1 results is compared. For INT3 sessions, results are typically available within 24 hours, while it takes two to three days for INT2 sessions, due to observations occurring on weekends. This reveals that the increased data volume recorded by the up to five stations with 1 Gbps does not increase the latency of the analysis results and dUT1 estimates can be obtained within 24-hours. </p><p>Overall, this work provides a detailed insight into the INT2 and INT3 session performances, revealing a strong positive trend in the precision of dUT1 measurements over the last few years.</p>

One of the core products of VLBI is the rapid determination of the Earth rotation parameter, expressed through dUT1. Multiple so-called Intensive observing programs exist that are observing dUT1 on a regular basis. Within this work, a detailed overview over the last five years of the VLBI Intensive observing programs INT2 and INT3 is provided. INT2 sessions are typically observed with a single baseline using a recording rate of $${256}\,\hbox {Mbps}$$ while INT3 sessions are multi-baseline Intensives with up to five stations and a recording rate of $${1}\,\hbox {Gbps}$$ . The median dUT1 precision estimated from INT2 sessions is $${10.5}\,{\mu }\hbox {s}$$ while it is $${5.9}\,\mu \hbox {s}$$ for INT3 sessions. The best performing INT2 baseline is between station MK-VLBA and WETTZELL with a median dUT1 formal error of $${6.4}\,\mu \hbox {s}$$ and showing only a small bias of $${-2.5}\,\mu \hbox {s}$$ w.r.t. the JPL EOP2 series. Starting in 2019, the scheduling strategy of the INT3 sessions was significantly changed, leading to a reduction in the estimated average dUT1 formal errors by 25 % for 4-station sessions and 45 % for 5-stations sessions. Mid-2020, the same change was performed for INT2 sessions, leading to a reduction in the average dUT1 mean formal error of up to 44 % for the baseline between MK-VLBA and WETTZELL. It is further revealed that the precision of single-baseline INT3 analysis is not significantly better than its INT2 counterpart, although a four-times higher data-rate is used. The reason for this is differences in scheduling optimization. On average, the mean formal error of the best single-baseline INT3 analysis is 50 % higher compared to utilizing the whole network. Besides analyzing dUT1 formal errors, the latency of the dUT1 results is compared for three analysis centers. For INT3 sessions, results are typically available within 24 hours, while it takes two to three days for INT2 sessions, due to observations occurring on weekends. Overall, this work provides detailed insight into the INT2 and INT3 session performances while revealing a strong positive trend in the precision of dUT1 measurements over the last years due to changes in the scheduling strategy.

Multi-year sea level estimation at O´Higgins station using GNSS interferometric reflectometry Ole Roggenbuck, Axel Rülke, Elke Kühmstedt, Christian Plötz Bundesamt für Kartographie und Geodäsie, Richard-Strauss-Allee 11, 60598 Frankfurt am Main Precise knowledge of the local ocean tides is important to correct space geodetic observations for ocean tide loading displacements. In remote areas as Antarctica ocean tide models still suffer from limited coverage of satellite altimetry observations in high latitudes and especially in coastal areas. The coverage of tide gauges is poor in this region and their continues operation is still a challenge due to harsh environmental conditions. The GNSS interferometric reflectometry (GNSS-R) is a promising method for continues observations of the sea surface heights (SSH) near the coast. In GNSS-R the signal to noise ratio (SNR) is analyzed to obtain the height difference between the GNSS antenna phase center and the reflecting sea surface. The method determines the sea surface height directly in the global reference system. The German Antarctic Receiving Station (GARS) O’Higgins is located at the northern tip of the Antarctic Peninsula and jointly operated by the German Aerospace Center (DLR) and the German Federal Agency for Cartography and Geodesy (BKG). The radio telescope is used for VLBI observations within the International VLBI Service. In this study we analysed 1 Hz GNSS observation data from the GNSS marker OHI3 at O’Higgins in order to determine SSH. We analysed several years of data using an inverse modelling approach. We introduce the method and assess their error budget. The GNSS-R results are compared to simultaneous campaign-wise tide gauge observations. The multi-year solution is used to estimate a set of tidal harmonics which is compared to existing ocean tide models.

Within this work, a new geodetic very long baseline interferometry (VLBI) scheduling approach inspired by evolutionary processes based on selection, crossover and mutation is presented. It mimics the biological concept “surviving of the fittest” to iteratively explore the scheduling parameter space looking for the best solution. Besides providing high-quality results, one main benefit of the proposed approach is that it enables the generation of fully automated and individually optimized schedules. Moreover, it generates schedules based on transparent rules, well-defined scientific goals and by making decisions based on Monte Carlo simulations. The improvements in terms of precision of geodetic parameters are discussed for various observing programs organized by the International VLBI Service for Geodesy and Astrometry (IVS), such as the OHG, R1, and T2 programs. In the case of schedules with a difficult telescope network, an improvement in the precision of the geodetic parameters up to 15% could be identified, as well as an increase in the number of observations of up to 10% compared to classical scheduling approaches. Due to the high quality of the produced schedules and the reduced workload for the schedulers, various IVS observing programs are already making use of the evolutionary parameter selection, such as the AUA, INT2, INT3, INT9, OHG, T2 and VGOS-B program.

Very Long Baseline Interferometry (VLBI) serves as one of the common geodetic methods to define the global reference frames and monitor Earth's 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.

Since mid-2020, various Very Long Baseline Interferometry (VLBI) observation programs organized by the International VLBI Service for Geodesy and Astrometry (IVS) are scheduled using a new algorithm inspired by evolutionary processes based on selection, crossover and mutation. It mimics the biological concept "survival of the fittest" to iteratively explore the scheduling parameter space looking for the best solution. In this work, we will present the general workflow of the algorithm as well as discuss its strengths and potential weaknesses. Moreover, we will highlight how the improved scheduling affects the precision of geodetic parameters. In the case of difficult-to-schedule OHG sessions, an improvement in the precision of the geodetic parameters of up to 15% could be identified based on Monte-Carlo simulations, as well as an increase in the number of observations of up to 10% compared to classical scheduling approaches.

The newly founded DACH Operation Center is a joint cooperation between the Federal Agency for Cartography and Geodesy in Germany (BKG), ETH Zurich (ETHZ), and Technische Universität Wien (TU Wien). The main motivation to establish a new Operation Center (OC) was to bring together the scheduling expertise at TU Wien and ETHZ and the technical and operational expertise at BKG. Together, it was possible to develop a fully automated scheduling procedure that is currently used for various IVS observation programs such as AUA, OHG, T2, INT2, INT3, EUVGOS, VGOS-B, and more. Within the cooperation, BKG is responsible for the technical aspects and is ensuring the long-term stability of the OC, while ETHZ and TU Wien are focusing on scientific studies and potential improvements to VLBI scheduling such as the newly developed scheduling parameter optimization based on Artificial Intelligence. 1 General Information With the retirement of Arno Müskens, who had maintained the scheduling activities at the University of Bonn (IGG) for the last 30 years, the official IVS sessions supervised at Bonn had to be transferred to another Operation Center (OC). Around the same time, a new VLBI scheduling software was developed at 1. ETH Zürich 2. Federal Agency for Cartography and Geodesy 3. Technische Universität Wien DACH Operation Center IVS 2019+2020 Biennial Report TU Wien: VieSched++1 [1]. To test the new scheduling software and to ensure a smooth transition of the scheduling activities from Bonn to a suitable successor, first tests were started in late 2018 by using the new scheduling software supervised at TU Wien. Initially, the work focused on improving the scheduling of the T2 sessions; but soon other observation programs followed. Meanwhile, it was decided that Wettzell should be designated as a new Operation Center and continue the work of Arno Müskens to ensure the long-term stability of the scheduling activities. Because there was evidence of significant improvement gained by using VieSched++ and by following the scheduling approaches developed at TU Wien, VieSched++ was selected as the scheduling software to be run by the Wettzell OC operationally. To ensure a generation of high-quality schedules and to benefit from the scheduling experience gained with the first tests of VieSched++, a cooperation between TU Wien and BKG was founded in 2019. With the move of Matthias Schartner, the main developer of the VieSched++ software package, from TU Wien to ETH Zürich, a third institution joined the cooperation, so that the BKG, the ETH Zürich, and the TU Wien jointly performed the assigned scheduling tasks in the context of the Operation Center Wettzell. In late 2020, it was decided to bundle the current activities as a joint Operation Center called “DACH”2 to streamline the activities and reduce the confusion about official responsibilities. 1 https://github.com/TUW-VieVS/VieSchedpp 2 https://www.bkg.bund.de/DE/Observatorium-Wettzell/IVSVLBI-Operations Center/IVS-VLBI-Operations Center.html

Context. Γ-ray detected radio-loud narrow-line Seyfert 1 (γ-NLS1) galaxies constitute a small but interesting sample of the γ-ray loud AGN. The radio-loudest γ-NLS1 known, PKS 2004−447, is located in the southern hemisphere and is monitored in the radio regime by the multiwavelength monitoring program TANAMI. Aims. We aim for the first detailed study of the radio morphology and long-term radio spectral evolution of PKS 2004−447, which are essential to understand the diversity of the radio properties of γ-NLS1s. Methods. The TANAMI VLBI monitoring program uses the Australian Long Baseline Array (LBA) and telescopes in Antarctica, Chile, New Zealand, and South Africa to monitor the jets of radio-loud active galaxies in the southern hemisphere. Lower resolution radio flux density measurements at multiple radio frequencies over four years of observations were obtained with the Australia Telescope Compact Array (ATCA). Results. The TANAMI VLBI image at 8.4 GHz shows an extended one-sided jet with a dominant compact VLBI core. Its brightness temperature is consistent with equipartition, but it is an order of magnitude below other γ-NLS1s with the sample value varying over two orders of magnitude. We find a compact morphology with a projected large-scale size < 11 kpc and a persistent steep radio spectrum with moderate flux-density variability. Conclusions. PKS 2004−447 appears to be a unique member of the γ-NLS1 sample. It exhibits blazar-like features, such as a flat featureless X-ray spectrum and a core dominated, one-sided parsec-scale jet with indications for relativistic beaming. However, the data also reveal properties atypical for blazars, such as a radio spectrum and large-scale size consistent with Compact-Steep-Spectrum (CSS) objects, which are usually associated with young radio sources. These characteristics are unique among all γ-NLS1s and extremely rare among γ-ray loud AGN.

We present results from the analysis of observations of the Chang’e 3 lander using geodetic Very Long Baseline Interferometry. The applied processing strategy as well as the limiting factors to our approach is discussed. We highlight the current precision of such observations and the accuracy of the estimated lunar-based parameters, i.e., the lunar lander’s Moon-fixed coordinates. Our result for the position of the lander is 44.12193^∘N , - 19.51159^∘E and - 2637.3 m, with horizontal position uncertainties on the lunar surface of 8.9 m and 4.5 m in latitude and longitude, respectively. This result is in good agreement with the position derived from images taken by the Narrow Angle Camera of the Lunar Reconnaissance Orbiter. Finally, we discuss potential improvements to our approach, which could be used to apply the presented concept to high-precision lunar positioning and studies of the Moon.

In the framework of the TANAMI multi-wavelength and VLBI monitoring, we study the evolution of the parsec-scale radio emission in radio galaxies in the southern hemisphere and their relationship to the γ-ray properties. In this first paper, we focus on Fermi-LAT-detected sources. We perform a kinematic analysis for five γ-ray detected radio galaxies using multi-epoch 8.4 GHz VLBI images, deriving limits on intrinsic jet parameters. We analyzed Fermi-LAT data in order to study possible connections between the γ-ray properties and the pc-scale jets of Fermi-LAT-detected radio galaxies, both in terms of variability and average properties. We discuss the individual source results and draw preliminary conclusions on sample properties including published VLBI results from the MOJAVE survey, with a total of fifteen sources. We find that the first γ-ray detection of Pictor A might be associated with the passage of a new VLBI component through the radio core. For the peculiar AGN PKS 0521-36, we detect subluminal parsec-scale jet motions, and we confirm the presence of fast γ-ray variability in the source down to timescales of 6 hours. We robustly confirm the presence of significant superluminal motion, up to β_app∼3, in the jet of the TeV radio galaxy PKS 0625-35. Finally, we place a lower limit on the age of the Compact Symmetric Object (CSO) PKS 1718-649. We draw some preliminary conclusions on the relationship between pc-scale jets and γ-ray emission in radio galaxies. We find that the VLBI core flux density correlates with the γ-ray flux, as seen in blazars. On the other hand, the γ-ray luminosity does not show any dependence on the core brightness temperature and core dominance, two indicators of Doppler boosting, suggesting that γ-ray emission in radio galaxies is not driven by orientation-dependent effects.

The Geodetic Observatory Wettzell features three radio-telescopes dedicated to Geodesy: the 20-m telescope Wz (internally called RTW – Ratioteleskop Wettzell) has been in operation since 1984, and the two 13.2-m TWIN telescopes. Wn (TWIN 1, called “Wettzell North” by the IVS Coordinating Center) and Ws (Wettzell South) are VGOS-capable and were inaugurated in 2013. Wn is currently equipped with a triband receiving system (S/X/Ka) and regularly participates in routine IVS operations. Ws is equipped with a VGOS Elevenfeed and participates in the VGOS Pilot Test phase. Together, these three telescopes form a local triangle. The analysis software LEVIKA SBA (Short Baseline Analysis) was developed at the Observatory for local VLBI data adjustment. It serves the primary purpose of determining the relative positions of the three telescopes from original VLBI data and comparing these results with the local tie vectors from the precision engineering network regularly surveyed at Wettzell. In addition, the software was developed as part of a quality management initiative, in order to provide timely feedback to the engineers and operators regarding the health status of the overall system. Since telescopes with substantially different receiving systems are present at Wettzell, mixed-mode observations and analysis are of importance. This contribution depicts the analysis software, its functional basics and presents selected analysis results. 1. Geodetic Observatory Wettzell, Federal Agency for Cartography and Geodesy (BKG), Sackenrieder Str. 25, D-93444 Bad Kötzting, Germany 2. University of the Federal Armed Forces Munich, Faculty of Aerospace Engineering, Werner-Heisenberg-Weg 39, D-85577 Neubiberg, Germany

Scheduling is an integral part of every VLBI experiment and, at this stage, already determines the geometric stability of the final solution. To increase the quality of the schedule, the TU Wien scheduling concept consists of two steps. The newly developed VLBI scheduling software VieSched++ offers the possibility to generate hundreds of different schedules for a single experiment automatically. Each of these schedules is then simulated hundreds of times using the VieVS VLBI module ending up with hundred thousands of simulations for a single experiment. The results are used to investigate the connection between scheduling optimization criteria and scheduling parameters with geodetic results gained during the analysis of simulations for the selection of the best suited schedule for the session at hand. In this work, we are providing an in-depth analysis of these correlations for the schedule of the T2129 session. We will show the importance of OHIGGINS for this network and highlight which optimization criteria play the biggest role in this session.