Journal of Geodesy

, Volume 90, Issue 3, pp 287–303 | Cite as

Improvement of the IVS-INT01 sessions by source selection: development and evaluation of the maximal source strategy

Original Article


The primary purpose of the International very long baseline interferometry (VLBI) Service for Geodesy and Astrometry Intensive sessions is the rapid estimation of UT1-TAI. Improving the robustness and the precision of the UT1 estimates from the Intensives is an important goal. The INT01 series, which usually uses the Kokee–Wettzell baseline and runs on weekdays, is the most regular IVS Intensive series. The United States Naval Observatory which schedules these sessions traditionally used a small list of strong sources. In 2009, the authors requested and received the use of nine IVS R&D sessions for the evaluation of a new strategy which draws on all sources mutually visible on the Kokee–Wettzell baseline. Analysis of these sessions was sufficiently promising that in July 2010, USNO began to alternate the use of the original and the new strategy in scheduling the INT01 sessions to assess the operational effectiveness of the proposed strategy. In this paper, we summarize our analysis of the R&D sessions, and we also analyze 2 years of operational INT01 sessions. Considered in toto, the new strategy performs as well as, or better than, the original strategy in terms of several measures of robustness and precision. Furthermore, the RMS difference of the UT1 estimates from the 1 h operational INTO1 sessions and concurrently run 24 h VLBI sessions is 21.0 \(\upmu \)s, compared to 30.7 \(\upmu \)s using the standard strategy, indicating that the new strategy is, on average, 30 % more accurate.


Very long baseline interferometry (VLBI) Space geodesy UT1 Radio astronomy 



This work was supported under NASA contract NNG12HP00C. The authors would like to thank David Gordon (NVI, Inc.) for providing helpful advice about using the Greenwich Sideal Time (GST) to compare the Intensive sessions. We would also like to thank Daniel MacMillan (NVI, Inc.) for providing information about atmospheric turbulence simulations and assistance in configuring them. We would like to thank Kerry Kingham and David Hall (USNO) for their support of the alternating operational IVS-INT01 sessions. Especially, we would like to thank Merri Sue Carter (USNO Flagstaff Station) for her scheduling of the alternating operational IVS-INT01 sessions.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.NVI, Inc.GreenbeltUSA

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