Observing UT1‑UTC with VGOS

We present first results for the determination of UT1-UTC using the VLBI Global Observing System (VGOS). During\ua0December 2019 through February 2020, a series of 1 h long observing sessions were performed using the VGOS stations\ua0at Ishioka in Japan and the Onsala twin telescopes in Sweden. These VGOS-B sessions were observed simultaneously\ua0to standard legacy S/X-band Intensive sessions. The VGOS-B data were correlated, post-correlation processed,\ua0and analysed at the Onsala Space Observatory. The derived UT1-UTC results were compared to corresponding results\ua0from standard legacy S/X-band Intensive sessions (INT1/INT2), as well as to the final values of the International Earth\ua0Rotation and Reference Frame Service (IERS), provided in IERS Bulletin B. The VGOS-B series achieves 3–4 times lower\ua0formal uncertainties for the UT1-UTC results than standard legacy S/X-band INT series. The RMS agreement w.r.t. to\ua0IERS Bulletin B is slightly better for the VGOS-B results than for the simultaneously observed legacy S/X-band INT1\ua0results, and the VGOS-B results have a small bias only with the smallest remaining standard deviation

Combining VGOS, legacy S/X and GNSS for the determination of UT1

We perform a combination on the observation level (COL) between VLBI and co-located GNSS in the context of VLBI intensive sessions. Our approach revolves around an estimation procedure which uses 3 h of GNSS data that uniformly encapsulate the 1-h VLBI data, in order to provide consistent troposphere information. We test this approach on both VGOS and Legacy S/X using the VGOS-B and concurrently observed INT1 sessions. The COL strategy is found to increase the precision by 15 % over both session types and leads to an increase of 65 % in the agreement between the sessions when estimating tropospheric gradients every 3 h. A more frequent estimation of the gradients every 1 h, which can be rigorously pursued with the utilization of multi-GNSS, results in a further convergence of the two session types by 30 %. The COL-aided length-of-day (LOD) products also show a 55 % better agreement to external GNSS-derived LOD. In the light of the increasing precision of broadcast GNSS orbits and clocks, this COL strategy can be used to derive rapid UT1-UTC products

VGOS VLBI Intensives between MACGO12M and WETTZ13S for the rapid determination of UT1-UTC

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 $\sigma_{UT1-UTC}$ of 3.1 $\mu$s and a bias w.r.t. IERS C04 of 1.1 $\mu$s. Later, the session performance decreased due to multiple technical difficulties.Comment: 8 pages, 5 figure

Evaluating the feasibility of short-integration scans based on the 2022 VGOS-R&D program

In this work, we report on activities focusing on improving the observation strategy of the Very Long Baseline Interferometry (VLBI) Global Observing System (VGOS). During six dedicated 24-hour Research and Development (R&D) sessions conducted in 2022, the effectiveness of a signal-to-noise ratio (SNR)-based scheduling approach with observation times as short as 5-20 seconds was explored. The sessions utilized a full 8 Gbps observing mode and incorporated elements such as dedicated calibration scans, a VGOS frequency source-flux catalog, improved sky-coverage parameterization, and more. The number of scans scheduled per station increased by 2.34 times compared to operational VGOS-OPS sessions, resulting in a 2.58 times increase in the number of observations per station. Remarkably, the percentage of successful observations per baseline matched the fixed 30-second observation approach employed in VGOS-OPS, demonstrating the effectiveness of the SNR-based scheduling approach. The impact on the geodetic results was examined based on statistical analysis, revealing a significant improvement when comparing the VGOS-R\&D program with VGOS-OPS. The formal errors in estimated station coordinates decreased by 50 %. The repeatability of baseline lengths improved by 30 %, demonstrating the enhanced precision of geodetic measurements. Furthermore, Earth orientation parameters exhibited substantial improvements, with a 60 % reduction in formal errors, 27 % better agreement w.r.t. IVS-R1/R4, and 13 % better agreement w.r.t. IERS EOP 20C04. Overall, these findings strongly indicate the superiority of the VGOS-R&D program, positioning it as a role model for future operational VGOS observations

Observations of radio sources near the Sun

Geodetic Very Long Baseline Interferometry (VLBI) data are capable of measuring the light deflection caused by the gravitational field of the Sun and large planets with high accuracy. The parameter $\gamma$ of the parametrized Post-Newtonian (PPN) formalism estimated using observations of reference radio sources near the Sun should be equal to unity in the general relativity. We have run several VLBI experiments tracking reference radio sources from 1 to 3 degrees from the Sun. The best formal accuracy of the parameter $\gamma$ achieved in the single-session mode is less than 0.01 percent, or better than the formal accuracy obtained with a global solution included all available observations at arbitrary elongation from the Sun. We are planning more experiments starting from 2020 using better observing conditions near the minimum of the Solar activity cycle.Comment: Proceeding of the EVGA 2019 Meeting. arXiv admin note: substantial text overlap with arXiv:1806.1129

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

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Optimizing geodetic VLBI schedules with VieSched++

Die Very Long Baseline Interferometry (VLBI) ist ein geodätisches Weltraumverfahren, welches global verteilte Teleskope benützt, um Signale von extragalaktischen Radioquellen zu beobachten. Durch die unterschiedlichen Ankunftszeiten der Signale an den Stationen, welche durch Kreuzkorrelation bestimmt werden, können die Positionen und Bewegungen der Teleskope sowie die Position von Radioquellen und die Orientierung der Erde bestimmt werden. Da mehrere Stationen gleichzeitig dieselbe Quelle beobachten müssen, ist es notwendig einen Beobachtungsplan zu erstellen. Die Erzeugung eines solchen Beobachtungsplans kann als ein komplexes Optimierungsproblem betrachtet werden. Es müssen die Beobachtungszeiten und die Beobachtungsabfolge unter Einhaltung vieler Nebenbedingungen optimal angeordnet werden. In dieser Arbeit wird das Problem des Erzeugens von VLBI Beobachtungsplänen erörtert und alle dafür nötigen Modelle und Algorithmen wie subnetting, fillin-mode und tagalong-mode erklärt. Der Hauptteil der Arbeit befasst sich mit der Entwicklung einer neuen, modernen Software namens VieSched++. Alle Algorithmen von VieSched++ wurden basierend auf Erfahrungen von anderen Softwarelösungen und Simulationen für diese Software neu entwickelt. Die Algorithmen werden im Detail erklärt und diskutiert. Die VLBI Beobachtungspläne werden von vielen verschiedenen und miteinander verwobenen Parametern beeinflusst. VieSched++ versucht dabei, einen optimalen Parametersatz zu finden. Dafür erzeugt die Software viele verschiedene Beobachtungspläne mit unterschiedlichen Parametern. Diese Beobachtungspläne können in Folge basierend auf Monte-Carlo Simulationen verglichen werden. VieSched++ wird bereits operationell für Beobachtungsprogramme des International VLBI Service for Geodesy and Astrometry (IVS) und für andere Anwendungen eingesetzt. Erste Resultate zeigen eine signifikante Verbesserung der Genauigkeit der geodätischen Parameter. Dabei wurde die Anzahl an Beobachtungen für das T2 Beobachtungsprogramm um einen Faktor von zwei bis drei erhöht. Außerdem wurde das EURR&D Beobachtungsprogramm signifikant verbessert. Im Durchschnitt wurden die Genauigkeiten um einen Faktor von zwei bis drei verbessert. Zusammenfassend kann gesagt werden, dass sich diese Arbeit mit der Notwendigkeit des Verbesserns von geodätischen VLBI Beobachtungsplänen befasst und zeigt wie diese Verbesserungen erreicht werden können.Very Long Baseline Interferometry (VLBI) is a technique that uses globally distributed radio telescopes to observe signals from extragalactic objects to measure their difference in arrival time at the telescopes by cross-correlation. Thereby, VLBI measures the positions and movements of these telescopes as well as the positions of the observed sources and orientation of the Earth in space. Since multiple stations have schedule, has to be generated. The generation of a geodetic VLBI schedule can be seen as an advanced optimization problem. It is necessary to optimize the time and observations of every telescope while many boundary conditions exist. A geodetic VLBI schedule is typically generated scan after scan by testing and evaluating all possibilities. In this work, a general overview about VLBI scheduling is given followed by a discussion of the models and concepts which are used in existing scheduling software, such as subnetting, fillin-mode, and tagalong-mode. The main topic of this thesis is the development of a new VLBI scheduling software which is called VieSched++. The software is written in modern C++ for enhanced performance and uses an objectoriented software design. Every algorithm in VieSched++ is developed from scratch based on the knowledge gained through analyzing existing schedules and scheduling software. The design ideas of these algorithms are discussed in this work in all details. Since VLBI scheduling is a complex task with many parameters and requirements interfering with each other, VieSched++ is designed to optimize schedules based on a brute-force approach, meaning, that it does not only generate one schedule for a session but is able to generate hundreds of schedules simultaneously by using different scheduling input parameters. These schedules can then be compared based on scheduling statistics or through Monte-Carlo simulations to pick the most appropriate schedule for the given session and scientific goal. VieSched++ is already used to schedule multiple official observing programs for the International VLBI Service for Geodesy and Astrometry (IVS) and other parties. First results reveal a significant improvement in the accuracy of geodetic parameters during the analysis of sessions scheduled with VieSched++. It was possible to increase the number of observations for the T2 observing program by a factor of two to three and the schedules for the EURR&D program were also improved significantly. On average, the improvement in accuracy of the geodetic parameters is also a factor of two to three. In summary, this work highlights the need to improve geodetic VLBI scheduling and reveals how this can be achieved.14814

Advancements and Challenges in Operational VLBI Scheduling Automation, VGOS, and Future Prospects

The coordination of telescopes is paramount in VLBI observations, where a meticulously crafted schedule determines the observations available for analysis. Recent years have witnessed substantial enhancements in VLBI scheduling, notably by the introduction of novel scheduling software within the IVS community. At the same time, the development of the VGOS network created new challenges and opportunities. This presentation provides an overview of the current VLBI scheduling landscape, highlighting advances made in automation and the integration of VGOS. The focal point of the talk is a robust, fully automated scheduling pipeline inaugurated in 2020, standing as a resounding success story. The transition to automated scheduling has demonstrated its effectiveness by significantly improving numerous observing programs. Through carefully designed optimization metrics combined with Monte-Carlo-based scheduling, human biases could be reduced while simultaneously increasing operational robustness, resulting in a higher quality of VLBI products.Moreover, the talk illuminates the current situation of VGOS scheduling, pinpointing areas ripe for improvement. Although VGOS is considered to be operational, in VGOS scheduling, there are still many unfortunately often poorly documented workarounds necessary.Open challenges and issues are examined in depth to increase community awareness. In addition, the need for greater standardization is highlighted, allowing for further automation and increased robustness. The discussion draws on insights from the VGOS R&D sessions, analyzes the methodologies used in these sessions, and suggests ways to refine VGOS operational planning.