Optimizing schedules for the VLBI global observing system

Schartner, Matthias; Boehm, J.

doi:10.1007/s00190-019-01340-z

Cited by 14 publications

(12 citation statements)

References 14 publications

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“…The ZWD and gradients are varying phenomena and as such have to be parametrized in a way that allows for temporal variability while keeping the number of estimated parameters low in order to maintain an overdetermined equation system. This can be achieved by using piecewise linear offsets (PWLO) for the parametrization of the ZWD and gradients (Schuh and Böhm, 2013). PWLO are based on offsets at certain reference epochs and linear interpolation in between.…”

Section: Tropospheric Delay Parametrizationmentioning

confidence: 99%

“…Subsequently a first global solution was calculated by solving all sessions together in a multi-year solution. The global solution uses a combination of the datum free normal equation matrices of the single session analysis to estimate parameters with higher accuracy (Schuh and Böhm, 2013). The geodetic datum for the global solution was defined in an unconstrained adjustment by fixing some parameters to their a priori values, as described in Sect.…”

Section: Station Coordinate Estimationmentioning

confidence: 99%

“…Although sophisticated simulations (Petrachenko et al, 2009) already indicated that rapid gradients will be beneficial for VGOS analysis, this is the first time to see this effect with real data. It is expected that the improvement will even be more visible with further optimized VGOS schedules (Schartner and Böhm, 2020).…”

Section: Troposphere Parametrizationmentioning

confidence: 99%

“…This investigation revealed that shorter estimation intervals for the gradients of 15 min and slightly longer estimation intervals of 45 min for the ZWD, compared to typical S/X analysis values, are beneficial. However, the ongoing maturing of VGOS, especially in terms of improvements in its scheduling (Schartner and Böhm, 2020), will likely continue to change the ideal parametrization of the tropospheric estimates.…”

Section: Stationmentioning

confidence: 99%

“…In order to improve the accuracies of geodetic parameters determined with Very Long Baseline Interferometry (VLBI) observations, the International VLBI Service for Geodesy and Astrometry (IVS) (Nothnagel et al, 2017) has developed the VLBI Global Observing System (VGOS) (Petrachenko et al, 2009). This new system is based on smaller and faster VLBI radio telescopes, allowing for a significantly increased number of observations, thereby enabling an improved estimation of tropospheric parameters which are considered one of the major error sources in geodetic VLBI (Schuh and Böhm, 2013). A recent demonstration of the possibilities with VGOS based on a single baseline between WEST-FORD (USA) and the station GGAO12M (USA) is provided by Niell et al (2018).…”

Section: Introductionmentioning

confidence: 99%

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Unconstrained Estimation of VLBI Global Observing System Station Coordinates

2021

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Abstract. The International VLBI Service for Geodesy and Astrometry (IVS) is currently setting up a network of smaller and thus faster radio telescopes observing at broader bandwidths for improved determination of geodetic parameters. However, this new VLBI Global Observing System (VGOS) network is not yet strongly linked to the legacy S/X network and the International Terrestrial Reference Frame (ITRF) as only station WESTFORD has ITRF2014 coordinates. In this work, we calculated VGOS station coordinates based on publicly available VGOS sessions until the end of 2019 while defining the geodetic datum by fixing the Earth orientation parameters and the coordinates of the WESTFORD station in an unconstrained adjustment. This set of new coordinates allows the determination of geodetic parameters from the analysis of VGOS sessions, which would otherwise not be possible. As it is the concept of VGOS to use smaller, faster slewing antennas in order to increase the number of observations, shorter estimation intervals for the zenith wet delays and the tropospheric gradients along with different relative constraints were tested and the best performing parametrization, judged by the baseline length repeatability, was used for the estimation of the VGOS station coordinates.

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Section: Tropospheric Delay Parametrizationmentioning

confidence: 99%

Section: Station Coordinate Estimationmentioning

confidence: 99%

Section: Troposphere Parametrizationmentioning

confidence: 99%

Section: Stationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Unconstrained Estimation of VLBI Global Observing System Station Coordinates

2021

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VLBI measurement of the vector baseline between geodetic antennas at Kokee Park Geophysical Observatory, Hawaii

Niell

Barrett

Cappallo

et al. 2021

J Geod

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We measured the components of the 31-m-long vector between the two very-long-baseline interferometry (VLBI) antennas at the Kokee Park Geophysical Observatory (KPGO), Hawaii, with approximately 1 mm precision using phase delay observables from dedicated VLBI observations in 2016 and 2018. The two KPGO antennas are the 20 m legacy VLBI antenna and the 12 m VLBI Global Observing System (VGOS) antenna. Independent estimates of the vector between the two antennas were obtained by the National Geodetic Survey (NGS) using standard optical surveys in 2015 and 2018. The uncertainties of the latter survey were 0.3 and 0.7 mm in the horizontal and vertical components of the baseline, respectively. We applied corrections to the measured positions for the varying thermal deformation of the antennas on the different days of the VLBI and survey measurements, which can amount to 1 mm, bringing all results to a common reference temperature. The difference between the VLBI and survey results are 0.2 ± 0.4 mm, −1.3 ± 0.4 mm, and 0.8 ± 0.8 mm in the East, North, and Up topocentric components, respectively. We also estimate that the Up component of the baseline may suffer from systematic errors due to gravitational deformation and uncalibrated instrumental delay variations at the 20 m antenna that may reach ± 10 and −2 mm, respectively, resulting in an accuracy uncertainty on the order of 10 mm for the relative heights of the antennas. Furthermore, possible tilting of the 12 m antenna increases the uncertainties in the differences in the horizontal components to 1.0 mm. These results bring into focus the importance of (1) correcting to a common reference temperature the measurements of the reference points of all geodetic instruments within a site, (2) obtaining measurements of the gravitational deformation of all antennas, and (3) monitoring local motions of the geodetic instruments. These results have significant implications for the accuracy of global reference frames that require accurate local ties between geodetic instruments, such as the International Terrestrial Reference Frame (ITRF).

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Automated VLBI scheduling using AI-based parameter optimization

Schartner

Plötz

Soja

2021

J Geod

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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.

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Optimizing schedules for the VLBI global observing system

Cited by 14 publications

References 14 publications

Unconstrained Estimation of VLBI Global Observing System Station Coordinates

Unconstrained Estimation of VLBI Global Observing System Station Coordinates

VLBI measurement of the vector baseline between geodetic antennas at Kokee Park Geophysical Observatory, Hawaii

Automated VLBI scheduling using AI-based parameter optimization

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