VieSched++: A New VLBI Scheduling Software for Geodesy and Astrometry

2021

Earth Planets Space

Self Cite

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

Section: Scheduling and Observing The Vgos-b Sessionsmentioning

confidence: 99%

Observing UT1-UTC with VGOS

Haas

Matsumoto

2021

Earth Planets Space

Self Cite

“…The optimization of the schedules can be achieved using VieSched++ (Schartner and Böhm 2019) and in particular its multi-scheduling feature. For geodetic VLBI scheduling and in particular for VGOS scheduling, a proper selection of the so-called weight factors (Schartner and Böhm 2019) is elementary for generating an optimized schedule (Schartner and Böhm 2020).…”

Section: Schedulingmentioning

confidence: 99%

“…The idle time optimization criterion is mostly used as a precaution to make sure that every station is observing regularly. It gradually increases the probability of scheduling scans containing stations that were previously not scheduled for a longer period (Schartner and Böhm 2019).…”

Section: Schedulingmentioning

confidence: 99%

“…The weight factors ω define how much each optimization criterion contributes for to the scan selection (Schartner and Böhm 2019). One key aspect of optimized geodetic scheduling is to balance the different optimization criteria and thus scheduling approaches through the weight factors.…”

Section: Schedulingmentioning

confidence: 99%

“…Every schedule was generated by allowing subnetting (Gipson 2010) and using an iterative source selection (Schartner and Böhm 2019) with a minimum number of three scans per source. The iterative source selection requires that multiple schedules have to be generated iteratively to finalize the source selection for the final schedule.…”

Section: Table 1 Weight Factor Combinations Leading To the Best Schedule For The 12 + 1 And 18 + 1 Station Training Networkmentioning

confidence: 99%

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

Boehm

Nothnagel

2020

Earth Planets Space

Self Cite

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.

Dilution of Precision (DOP) Factors for Evaluating Observations to Galileo Satellites with VLBI

Wolf

Böhm

International Association of Geodesy Symposia

et al. 2022

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Installing a VLBI transmitter on Galileo satellites will allow observing satellites in parallel to quasars with Very Long Baseline Interferometry (VLBI) telescopes. This offers a variety of new applications such as the direct determination of the absolute orientation of the satellite constellation with respect to the International Celestial Reference Frame (ICRF) and the improvement of the Terrestrial Reference Frame (TRF) exploiting the possibilities of direct high precision tying of the different space geodetic equipment. In preparation of these observations by enhancing the capabilities of the VLBI scheduling program VieSched++, we perform an evaluation study of observations of a Galileo satellite employing Dilution of Precision (DOP) factors. The idea is to introduce DOP factors in the decision process of VieSched++ after a thorough assessment of DOP factors for individual parameters. In our study, we choose an existing network of VLBI Global Observing System (VGOS) type telescopes for observing Galileo satellite GSAT0212 within a 24 h arbitrary session. Preparing the DOP factor analysis, we first carry out a theoretical study to investigate the VLBI sensitivity to satellite orbit displacements in the local orbital frame with normal (radial), tangential and cross-track direction. This analysis shows that the highest sensitivity of a satellite observation is that of the tangential component if the direction of the satellite track is parallel to the direction of the observing baseline. A satellite observation is most sensitive towards the cross-track component if these two directions are orthogonal to each other. The DOP factor analysis itself is performed separating the satellite position again into its three components and adding a separate DOP factor for the UT1-UTC (dUT1) parameter. The periods, where satellite observations are possible, were determined using VieSched++. At a later stage, these DOP factors will be used as an optimization criterion for the scheduling process. The DOP factors of potential observations from the chosen VGOS network to GSAT0212 reach minimum DOP values of 27.13 in normal, 1.49 in tangential, and 1.67 in cross-track direction and 0.45 for determining dUT1. With these results, which have confirmed intuitive considerations on the relative magnitudes, we have laid the groundwork for using DOP factors as driving criteria in the scheduling process of Galileo satellites embedded in regular VLBI observations of quasars.