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

Pipeline for Large-Scale Microdroplet Bisulfite PCR-Based Sequencing Allows the Tracking of Hepitype Evolution in Tumors

Cytosine methylation provides an epigenetic level of cellular plasticity that is important for development, differentiation and cancerogenesis. We adopted microdroplet PCR to bisulfite treated target DNA in combination with second generation sequencing to simultaneously assess DNA sequence and methylation. We show measurement of methylation status in a wide range of target sequences (total 34 kb) with an average coverage of 95% (median 100%) and good correlation to the opposite strand (rho = 0.96) and to pyrosequencing (rho = 0.87). Data from lymphoma and colorectal cancer samples for SNRPN (imprinted gene), FGF6 (demethylated in the cancer samples) and HS3ST2 (methylated in the cancer samples) serve as a proof of principle showing the integration of SNP data and phased DNA-methylation information into “hepitypes” and thus the analysis of DNA methylation phylogeny in the somatic evolution of cancer

Optimal antenna locations of the VLBI Global Observing System for the estimation of Earth orientation parameters

To support monitoring subtle effects in the Earth system such as a mean sea level rise of 3 mm/year, a next-generation VLBI system, the VLBI Global Observing System (VGOS), has been developed and a new VGOS station network is being built. However, the geometry of the current VGOS network and its planned extension suffer from a lack of stations in the southern hemisphere. In this investigation, we identify optimal locations for additional VGOS radio telescopes with a new method based on bulk observing schedule generation and subsequent large-scale Monte-Carlo simulations. The location of the additional station is varied over 477 possible locations, homogeneously distributed over land areas on the globe. For each antenna location, several schedules have been generated and simulated to minimize the effects of scheduling and the randomness of simulations. Thereby, it is possible to judge, in which regions an additional VGOS station would have the biggest impact on the precision of the estimated geodetic parameters, in our case assessed by the repeatabilities of the estimated Earth orientation parameters (EOPs). To generate highly optimized schedules and to remove effects due to non-optimized scheduling, a total of 93 thousand schedules were iteratively generated, investigating over 300 billion scans and 2.4 trillion observations. Each schedule was further simulated 1000 times, leading to over 5 trillion simulated and analyzed observations. Although the optimum location of a future VLBI station depends on the EOP of interest and the geometry of the existing network, it is shown that the more the VGOS network grows, the more the lack of southern stations becomes prominent. The best location for an additional VGOS station for most EOP components and especially in the case of future VGOS networks would be the southern part of South America. It is further shown that the location of the additional antenna highly determines the expectable precision of the EOP estimates. For a 6-station network, the location of an additional seventh antenna can improve the precision of the EOP by a factor of 2.4 to 3.8. For an 18-station network, the location of an additional 19th station still improves the repeatability by a factor of 1.6. It is also found that adding a station at some locations will not improve the precision at all.ISSN:1343-8832ISSN:1880-598

Optimal VLBI baseline geometry for UT1-UTC Intensive observations

One of the main tasks of Very Long Baseline Interferometry (VLBI) is the rapid determination of the highly variable Earth’s rotation expressed through the difference between Universal Time UT1 and Coordinated Universal Time UTC (dUT1). For this reason, dedicated one hour, single baseline sessions, called “Intensives”, are observed on a daily basis. Thus far, the optimal geometry of Intensive sessions was understood to include a long east–west extension of the baseline to ensure a dUT1 estimation with highest accuracy. In this publication, we prove that long east–west baselines are the best choice only for certain lengths and orientations. In this respect, optimal orientations may even require significant inclination of the baseline with respect to the equatorial plane. The basis of these findings is a simulation study with subsequent investigations in the partial derivatives of the observed group delays τ with respect to dUT1 ∂τ/∂dUT1. Almost 3000 baselines between artificial stations located on a regular 10×10 degree grid are investigated to derive a global and generally valid picture about the best length and orientation of Intensive baselines. Our results reveal that especially equatorial baselines or baselines with a center close to the equatorial plane are not suited for Intensives although they provide a good east–west extension. This is explained by the narrow right ascension band of visible sources and the resulting lack of variety in the partial derivatives. Moreover, it is shown that north–south baselines are also capable of determining dUT1 with reasonable accuracy, given that the baseline orientation is significantly different from the Earth rotation axis. However, great care must be taken to provide accurate polar motion a priori information for these baselines. Finally, we provide a better metric to assess the suitability of Intensive baselines based on the effective spread of ∂τ/∂dUT1.ISSN:0949-7714ISSN:1432-139

Precision of Galileo satellite orbits obtained from simulated VLBI observations

Observing Earth-orbiting satellites additionally to natural extra-galactic radio sources with Very Long Baseline Interferometry (VLBI) radio telescopes offers a variety of new possibilities and allows expanding the research activities of this highly accurate technique. The combination of observations to satellites and quasars permit the determination of the satellite orbit from VLBI observations in the terrestrial as well as in the International Celestial Reference Frame. The latter is enabled by the unique capability of VLBI to determine Universal Time UT1. In this contribution for the first time, the precision of short satellite orbital arcs determined with simulated VLBI observations to Galileo satellites for different observation geometries using various VLBI networks and arc lengths is investigated. For this purpose, schedules including both, observations to quasars and satellites, are created using the scheduling software VieSched++. The simulations of the scheduled observations and the estimation of the satellite arcs are carried out using the Vienna VLBI and Satellite Software (VieVS). The quality of the estimated orbits is investigated and assessed based on the mean formal errors and the repeatabilities of the individual components of the satellite positions based on Monte Carlo simulations

On the geometry of baselines suitable for UT1 estimation with VLBI Intensive sessions

One hour single baseline VLBI sessions, so-called Intensives, are routinely observed to derive UT1-UTC with a short latency. The selection of baselines for VLBI Intensive sessions and their application for the determination of UT1-UTC is a complex task. Thus far, it has been understood that long east-west extensions are critical for the accuracy of UT1-UTC. In this presentation, we show, that the answer is not as simple as that. We run Monte-Carlo simulations for a global 10° grid of artificial station locations and discuss the suitability of the individual baselines for UT1-UTC estimation based on the formal error of dUT1. The antennas are located at latitudes of -80° to 80° and longitudes of 0° to 180° and are assumed to have the same properties than the WETTZ13S telescope. The nine stations at longitude 0° on the northern hemisphere are defined as reference stations. In total, 2898 possible baselines between the reference stations and other artificial stations are investigated over one year based on monthly schedules to minimize potential seasonal variations. Thus, with this study, it is possible to derive a complete picture of which baselines are most suitable for dUT1 estimates. In general, the findings show optimal global geometries concerning Intensives. For example, we can confirm that the IVS-INT1 baseline including the stations Kokee and Wettzell is among the best ones available. Furthermore, we show that north-south baselines are also sensitive to dUT1 as long as their orientations are not parallel to the Earth rotation axis. Moreover, we highlight that east-west baselines on the equator are not suitable for estimating dUT1 due to the lack of variety in right-ascension of the visible sources. Additionally, we highlight, that very long baselines are problematic due to the highly restricted mutual visibility