Observing Program

CONT17

Continuous VLBI Campaign 2017

Citation reference. If you use CONT17 data in your papers and presentations please reference the following citation:

D. Behrend, C. Thomas, J. Gipson, E. Himwich, K. Le Bail, "On the organization of CONT17", J. Geod., 94:100, 2020. doi:10.1007/s00190-020-01436-x https://rdcu.be/b8q0I

Furthermore, please include an acknowledgement text in order to support the contributors of the campaign. The IVS Directing Board requests to use the wording as given in the Acknowledgements section.

Purpose

CONT17 is a campaign of continuous VLBI sessions, scheduled to be observed in November and December 2017 (28-NOV-2017 00:00 UT through 12-DEC-2017 24:00 UT). The CONT17 campaign will be a continuation of the series of very successful continuous VLBI campaigns that were observed at irregular intervals since 1994. The most recent CONT campaigns were observed in roughly three-year intervals as CONT05 (September 2005), and CONT08 (August 2008), CONT11 (September 2011), and CONT14 (May 2014). CONT17 differs from the previous CONT campaigns in that there will be three independent networks observed: two legacy networks will observe at S/X band, one VGOS network will do broadband observing. The VGOS broadband network will have a smaller size and will only be observed for about a third of the CONT17 period.

Goals

The plan for the CONT17 campaign is to acquire state-of-the-art VLBI data over a time period of about two weeks to demonstrate the highest accuracy of which the legacy S/X VLBI system is capable, to investigate possible network biases, and to demonstrate some of the VGOS capabilities limited by the size and geometry of the available VGOS network and observation period. This will support high resolution Earth rotation studies, investigations of reference frame stability, and investigations of daily to sub-daily site motions, among other things. A number of scientific and technical goals are set for the campaign:

• Science: Analysis of the two weeks of continuous high frequency (sub-daily) Earth Orientation Parameters (EOP) will address the discrepancies seen between the theoretical models (ocean tidal and atmospheric) and the observations at the M2 and S1 frequencies as well as between long-term and short-term values of tidal amplitudes. The two legacy networks of CONT17 have a reasonably balanced geographical distribution between the northern and southern hemispheres. Both networks are expected to provide at least comparable precision with respect to the most recent CONT campaigns. This will allow studies of high frequency EOP variations, analysis of ocean tide models, and tests of theoretical models using two independent data sets. It is also expected that the precision of CONT17 will further the studies of ter-diurnal signals related to M3 and S3 tidal phenomena in the oceans and the atmosphere. For ionospheric research, the large geographical coverage of CONT17 will allow the derivation of maps of total electron content (TEC) with an increased sensitivity to smaller scale features. Having two inpdendent data sets will allow to also get an estimate of the accuracy of the parameters of interest.
• Technique improvement: The two legacy S/X networks will be used to probe the accuracy of the VLBI estimates of the EOP and to investiate possible network biases. The VGOS broadband demonstration network will provide an initial indication of VGOS capabilities. Continuous VLBI data allows comparison of estimates of troposphere zenith delay and gradients across session boundaries as a measure of the accuracy of the observations and analysis. Experience from previous CONT campaigns shows the importance of observing tropospheric parameters with several complementary instruments for the derivation of robust geodetic results in particular for reference frame investigations. Comparisons with GPS estimates and with Numerical Weather Models (NWM) will be of great importance. High-resolution NWM are being used for the derivation of mapping functions. CONT17 will be an excellent test bed to develop this approach further by investigating the inclusion of atmospheric turbulence models and/or NWM derived tropospheric gradients in the geodetic VLBI analysis.
• Accuracy assessment: Analysis of reference frame repeatability day to day can be made with CONT17 and compared with previous continuous VLBI series. In particular the rigorous combination of reference frame realizations can be investigated. Continuous VLBI sessions have proven to be a very important source of information for these investigations.
• Comparisons: All stations have IGS GPS systems relatively nearby that are considered Global Stations, three stations are co-located with an ILRS SLR system, and four stations are co-located with an IDS DORIS station. The continuous high accuracy allows investigation of daily and sub-daily site motions for comparison with external factors such as atmospheric effects and temperature distortions of the antennas or pedestals.

Observation Period

The fifteen days of continuous VLBI observation have been fixed as follows:

Legacy S/X data will be taken over the entire period of CONT17. VGOS observations will be done for five days in the center week of CONT17 (December 4–8, 2017). In order to allow stations that participate both with a legacy S/X antenna and a VGOS broadband antenna sufficient time for a clean day changeover the actual start time of the VGOS observation day was shifted to one hour earlier. The fifth day of the VGOS observing period is 25 hours long so that the CONT17 VGOS observing days can be rearranged during correlation/analysis to directly coincide with the legacy S/X observing.

Network Resources

The following provides a description of the network resources that will be used during the CONT17 campaign.

Legacy S/X Stations

The geographical distribution of the two CONT17 legacy S/X networks is shown in the station distribution map. The names of the stations of the Legacy-1 (blue) and Legacy-2 (red) networks are listed in their corresponding tables.

• Legacy-1 observation network (blue network): 14 stations alloted observing time in this network for the 15 days of the CONT17 campaign. The stations are:
  
  

  Name	Code	Observatory name and location
  BADARY	Bd	Badary Radio Astronomical Observatory, Russia
  FORTLEZA	Ft	Space Radio Observatory of the Northeast (ROEN), Fortaleza, Brazil
  HART15M	Ht	Hartebeesthoek Radio Astronomy Observatory, South Africa
  HOBART26	Ho	Mt. Pleasant Radio Astronomy Observatory, Hobart, TAS, Australia
  KASHIM11	K1	Kashima VLBI Station, Japan
  KATH12M	Ke	Katherine Observatory, Katherine, NT, Australia
  KOKEE	Kk	Kokee Park Geophysical Observatory, Kauai, HI, USA
  MATERA	Ma	Centro di Geodesia Spaziale G. Colombo, Matera, Italy
  NYALES20	Ny	Ny Ålesund Geodetic Observatory, Spitsbergen, Norway
  ONSALA60	On	Onsala Space Observatory, Sweden
  WARK12M	Ww	Warkworth VLBI Station, New Zealand
  WETTZELL	Wz	Geodetic Observatory Wettzell, Germany
  YEBES40M	Ys	Astronomical Center at Yebes, Spain
  ZELENCHK	Zc	Radioastronomical Observatory Zelenchukskaya, Russia

  
  
• Legacy-2 observation network (red network): 14 stations alloted observing time in this network for the 15 days of the CONT17 campaign. The stations are:
  
  

  Name	Code	Observatory name and location
  BR-VLBA	Br	VLBA Station, Brewster, WA, USA
  FD-VLBA	Fd	VLBA Station, Ft. Davis, TX, USA
  HN-VLBA	Hn	VLBA Station, Hancock, NH, USA
  KP-VLBA	Kp	VLBA Station, Kitt Peak, AZ, USA
  LA-VLBA	La	VLBA Station, Los Alamos, NM, USA
  MK-VLBA	Mk	VLBA Station, Mauna Kea, HI, USA
  NL-VLBA	Nl	VLBA Station, North Liberty, IA, USA
  OV-VLBA	Ov	VLBA Station, Owens Valley, CA, USA
  PIETOWN	Pt	VLBA Station, Pie Town, NM, USA
  SC-VLBA	Sc	VLBA Station, St. Croix, VI, USA
  MEDICINA	Mc	Medicina Radio Astronomy Station, Italy
  SESHAN25	Sh	Shanghai Astronomical Observatory, Seshan, China
  WETTZ13N	Wn	Geodetic Observatory Wettzell, Germany
  YARRA12M	Ya	Yarragadee Observatory, Yarragadee, WA, Australia

VGOS Broadband Stations

The geographical distribution of the CONT17 VGOS broadband network and the names of the stations are described below.

• VGOS broadband demonstration network: 6 stations alloted observing time for this network for 5 session days of the CONT17 campaign. The stations are:
  
  

  Name	Code	Observatory name and location
  GGAO12M	Gs	Westford Antenna, Haystack Observatory, MA, USA
  ISHIOKA	Is	Ishioka VLBI Station, Japan
  KOKEE12M	K2	Kokee Park Geophysical Observatory, Kauai, HI, USA
  WESTFORD	Wf	Westford Antenna, Haystack Observatory, MA, USA
  WETTZ13S	Ws	Geodetic Observatory Wettzell, Germany
  RAEGYEB	Yj	Astronomical Center at Yebes, Spain

  
  * Note that Hobart (HOBART12) dropped out of the original list. Onsala (ONSA13NE) is still verifying the VGOS broadband signal chain.
  

Additional Station Items

The following summarizes a few more station-related items of CONT17:

• The CONT17 stations committed to a pre-campaign station checkout to ensure that the data acquired during the campaign are of the highest quality. The observing modes for the participating stations were tested in the even numbered IVS-R1 and in select IVS-RDV sessions. As a very late addition to the legacy networks, Seshan performed RFI tests for the frequencies used with the Legacy-2 network. All stations checked out fine. The VGOS stations are checked out in 24-hour VGOS test sessions.
• Rapid disk return for the "R" type sessions during the CONT17 period so that IVS can keep up its commitment for two rapid-turnaround sessions each week. The equivalents of the IVS-R1 and IVS-R4 sessions will be shipped/e-transferred and processed rapidly using the data of the Legacy-1 network.
• While the stations of the Legacy-1 network are expected to mostly e-transfer their data to the Bonn Correlator (only Kokee Park and Matera will ship physically), the Legacy-2 stations will have to ship their recording modules physically to the VLBA Correlator at Socorro.
• Simultaneous acquisition of high quality GPS data during the campaign so that the comparison analyses can be done. Coordination with the IGS community will be done to make sure that the stations can be expected to produce good data reliably.
• Simultaneous observing by co-located SLR systems at HartRAO, Wettzell, and Yarragadee.

Correlator Resources

With three networks to be correlated, the correlation load will be shared among three correlators for the CONT17 data itself. The Bonn Correlator will correlate the Legacy-1 network, the VLBA Correlator at Socorro will correlate the Legacy-2 network, and Haystack Observatory will correlate the VGOS demonstration network. While not doing CONT correlation per se, the Washington Correlator will assist the Bonn and Haystack correlators by reducing their work load in the regular IVS observing program prior to and after the CONT17 campaign.

Expected Accuracies

The schedules will be standard geodetic schedules which achieves simulated EOP results of at least as good as 25 µarcsec for pole position and 1.0 µs for UT1 for the legacy networks. A covariance analysis without velocity estimation resulted in the following EOP formal errors (likely too optimistic but intercomparable):

* Note that the simulation runs were done with only 13 stations each for the legacy networks (as Kashima and Seshan were added later), but with 8 stations for the VGOS-Demo network (including Hobart and Onsala).

Schedules

The detailed observing schedule for CONT17 will be generated using the automatic scheduling algorithms of the NASA sked program. We will investigate the best combination of scheduling parameters, minimum SNR levels, source list, and flux models. The “best” schedule will be determined as a compromise between the optimum simulated formal errors, number of observations, number of scans per hour, sky coverage, and robustness. Unlike previous CONT campaigns, CONT17 will not have daily station check times. However, there will be a fringe test prior to CONT17 to check the stations' sanity.

The Intensive sessions IVS-INT1, IVS-INT2, and RuI have precedence over CONT17 observing (no IVS-INT3 will be observed during CONT17). The four stations that observe in the Intensive sessions (Kokee Park and Wettzell for the IVS-INT1 and IVS-INT2, Badary and Zelenchukskaya for the RuI sessions) have scheduled gaps in the CONT17 observing schedules; these gaps are one hour plus a padding at either end for schedule switchovers of 15-min (Kokee Park, Wettzell) and 10-min (Badary, Zelenchukskaya), respectively. The "Intensive stations" will be scheduled in tag-along mode during their Intensive periods.

Acknowledgements

The IVS Directing Board decided that any publication that uses CONT17 data has to include an acknowledgement text in order to support the contributors of the campaign. Please use the following Acknowledgements text in your publications:

Acknowledgements. We are grateful to all parties that contributed to the success of the CONT17 campaign, in particular to the IVS Coordinating Center at NASA Goddard Space Flight Center (GSFC) for taking the bulk of the organizational load, to the GSFC VLBI group for preparing the legacy S/X observing schedules and MIT Haystack Observatory for the VGOS observing schedules, to the IVS observing stations at Badary and Zelenchukskaya (both Institute for Applied Astronomy, IAA, St. Petersburg, Russia), Fortaleza (Rádio Observatório Espacial do Nordeste, ROEN; Center of Radio Astronomy and Astrophysics, Engineering School, Mackenzie Presbyterian University, Sao Paulo and Brazilian Instituto Nacional de Pesquisas Espaciais, INPE, Brazil), GGAO (MIT Haystack Observatory and NASA GSFC, USA), Hartebeesthoek (Hartebeesthoek Radio Astronomy Observatory, National Research Foundation, South Africa), the AuScope stations of Hobart, Katherine, and Yarragadee (Geoscience Australia, University of Tasmania), Ishioka (Geospatial Information Authority of Japan), Kashima (National Institute of Information and Communications Technology, Japan), Kokee Park (U.S. Naval Observatory and NASA GSFC, USA), Matera (Agencia Spatiale Italiana, Italy), Medicina (Istituto di Radioastronomia, Italy), Ny Ålesund (Kartverket, Norway), Onsala (Onsala Space Observatory, Chalmers University of Technology, Sweden), Seshan (Shanghai Astronomical Observatory, China), Warkworth (Auckland University of Technology, New Zealand), Westford (MIT Haystack Observatory), Wettzell (Bundesamt für Kartographie und Geodäsie and Technische Universität München, Germany), and Yebes (Instituto Geográfico Nacional, Spain) plus the Very Long Baseline Array (VLBA) stations of the Long Baseline Observatory (LBO) for carrying out the observations under the US Naval Observatory's time allocation, to the staff at the MPIfR/BKG correlator center, the VLBA correlator at Socorro, and the MIT Haystack Observatory correlator for performing the correlations and the fringe fitting of the data, and to the IVS Data Centers at BKG (Leipzig, Germany), Observatoire de Paris (France), and NASA CDDIS (Greenbelt, MD, USA) for the central data holds.