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Balancing source strength and sky coverage in IVS-INT01 scheduling

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Abstract

The international very-long-baseline interferometry service for Geodesy and Astrometry’s INT01 sessions originally observed small sets of strong quasars (“sources”). But the sources were unevenly distributed, causing bad observation coverage and high UT1 formal errors at times of the year, especially early October. To improve coverage, in 2009, we introduced the maximal source strategy (“MSS”), the strategy of using all geodetic sources that are mutually visible at the two primary INT01 stations. But although the MSS reduced the UT1 formal errors from 32.0 to \(15.1\,\upmu \)s in the first half of October in 2 years of testing, the MSS increased them from 10.0 to \(12.0\,\upmu \)s in the first half of November; the MSS had introduced weaker sources, which take longer to observe, leading to fewer observations and higher UT1 formal errors. Starting in 2014, we investigated balancing source strength and sky coverage in source sets through their size and through the use of the Goddard Space Flight Center’s Sked program’s “Bestsource” command, which balances these factors. We used the UT1 formal error and two sensitivity metrics to evaluate schedules made from “balanced” source sets of seven sizes and selected 50 as the best size. We tested this “Balanced 50” (BA50) strategy against the MSS strategy in six R&D sessions. The results led to the BA50’s use in operational INT01 scheduling on a trial basis. We report on the selection of the BA50 strategy, the R&Ds that tested it, and its operational use.

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Data availability statement

The MSS and BA50 operational INT01 sessions and the 24-h R&D sessions are publicly available through the International VLBI Service for Geodesy and Astrometry (IVS) data archives. The uncorrected Intensive R&D sessions have names that do not fit the current IVS naming conventions, so we are working on finding a way to submit them to the IVS. We hope that they will be added to the IVS archives by early 2020. Meanwhile, the sessions may be requested from the corresponding author. The corrected Intensive R&D sessions used for analysis are not part of the standard IVS data set, but the data are available from the corresponding author upon reasonable request and with the permission of the National Aeronautics and Space Administration’s Goddard Space Flight Center (NASA GSFC).

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Acknowledgements

This work was supported by the National Aeronautics and Space Administration (NASA) under contracts NNG12HP00C and NNG17HS00C. The authors thank the International VLBI Service for Geodesy and Astrometry (IVS) (Behrend 2013) for allocating the six R&D sessions discussed in this paper. We thank the IVS OPC and Cynthia Thomas for supporting the special needs of the R&D sessions. We thank Chris Coughlin and the USNO/NASA Kokee Park station and Dr. Torben Schüler and the Bundesamt für Kartographie und Geodäsie’s Wettzell station for their observation of the six sessions and their assistance with the special needs of the sessions. We thank Mike Titus and the Massachusetts Institute of Technology’s Haystack Correlator for correlation of the data. We thank Merri Sue Carter (USNO Flagstaff) for testing a BA50 source set within the IVS-INT01 operational sessions. We thank the IVS for the use of its operational INT01 data. We thank Daniel MacMillan (NVI, Inc.) for providing information about atmospheric turbulence modeling. Finally, we thank David Gordon (NVI, Inc.) for providing helpful advice about using the Greenwich Sidereal Time (GST) to compare the Intensive sessions in our original study of the MSS.

Funding

The authors are employed by NVI, Inc. This work was supported by contracts NNG12HP00C and NNG17HS00C between the National Aeronautics and Space Administration (NASA) and NVI, Inc. The authors are associate members of the International VLBI Service for Geodesy and Astrometry (IVS), but receive no financial support from the IVS.

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Authors and Affiliations

  1. NVI, Inc., 7257D Hanover Parkway, Greenbelt, Maryland, 20770, USA

    Karen Baver & John Gipson

Authors
  1. Karen Baver
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  2. John Gipson
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Contributions

KB designed and performed the simulations. KB requested, designed, scheduled, and analyzed the R&D sessions. KB evaluated the operational BA50 sessions. KB wrote the paper. JG was the lead for the R&D accuracy analysis. JG also provided some technical advice and assisted with the 2014 simulation design, the request for R&D observing time, and some rephrasing during editing.

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Correspondence to Karen Baver.

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The authors are unaware of any other potential conflicts of interest.

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Baver, K., Gipson, J. Balancing source strength and sky coverage in IVS-INT01 scheduling. J Geod 94, 18 (2020). https://doi.org/10.1007/s00190-020-01343-1

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