IVS Observing Program

Session Descriptions: 2003

This section has brief descriptions of each type of session coordinated by IVS. Refer to the master files for the details of each session such as start times, participating stations, correlator, and current status.


IVS-R1 and IVS-R4:

The purpose of of the IVS-R1 and IVS-R4 sessions is to provide twice weekly EOP results on a timely basis. These sessions provide continuity with the previous NEOS and CORE series.

The "1" and "4" indicate that the sessions are on Mondays and Thursdays, respectively. Widely separate sessions during the week gives approximately even spacing between these two sessions for monitoring periodic terms in tides and nutation.

The "R" stands for rapid turnaround because the stations, correlators, and analysts have a commitment to make the the time delay from the end of recording to results as short as possible. The time delay goal is a maximum of 15 days. Participating stations are requested to ship tapes to the correlator as rapidly as possible. Tapes from the Monday session should arrive no later than Friday, tapes from the Thursday session (ending late on Friday) should be shipped as early on Monday as possible to arrive no later than Thursday.

Each network for R1 and R4 has 7 stations. There is a core network for each day plus one or two other stations. The R1 will be recorded with a data rate of 256 mbits. The R4s with Matera as a participating station will be recorded with a data rate of 56 mbits. The R4s with Tigo as a participating station will be recorded with a data rate of 112 mbits so that more scans per hour could be observed at Tigo.

The networks and correlators are:

Session Day Networks Correlator
R1 Monday Cycle through these networks:
R4 Thursday Cycle through these networks:


The purpose of the IVS-T2 sessions is to monitor the TRF via monthly sessions. All geodetic stations participate in at least two T2 sessions each year. These sessions replace the IRIS-S sessions observed in previous years until 2002.


The purpose of the IVS-E3 sessions is to provide an additional monthly EOP monitoring session. These sessions will use S2 technology for recording and processing. The network will be fixed because of the limited number of stations currently equipped with geodetic S2 capability. Stations are: Algonquin, Yellowknife, the Canadian Transportable VLBI Antenna (CTVA), TIGO, and Kokee. When more stations have geodetic S2 equipment these sessions may be expanded.


The INT1 and INT2 sessions are 1-baseline, 1-hour "intensive" sessions to monitor UT1. These sessions are designed to provide rapid service UT1 results. Sessions for INT1 are observed four times weekly. Sessions for INT2 are currently being coordinated and specific details will be posted later.

Session Days Baseline Correlator
I1 Mon,Tue,Wed,Fri Wettzell-Kokee WACO
I2 to be decided Wettzell-Tsukuba GSI


The primary purpose of the APSG sessions is to continue monitoring the relative motions of the plates in the Asia-Pacific region. These sessions involve sites on the four plates. Tsukuba and Fairbanks are on the North American Plate, Hobart is on the Australian Plate, Seshan and Urumqi are on the Eurasian Plate, and Kokee is on the Pacific Plate. Thus, these sessions will produce critical data for the investigation of the current crustal motions in the Asia-Pacific region combined with the data from the APSG SLR and GPS campaigns which will also be performed in the same month as the APSG experiments. Also, these experiments will improve the accuracy of the geocentric coordinates of the participating stations, especially Urumqi and Tuskuba.


The purpose of this experiment is to determine the station coordinates and their evolution in the European geodetic VLBI network. This process will be done with the highest precision possible.


The purpose of the IVS-OHIG (Southern Terrestrial Reference Frame) sessions is to tie together optimally the sites in the southern hemisphere. The participating sites include all the sites in the south - O'Higgins, Fortaleza, Hartebeesthoek, Hobart, TIGO - as well as Kokee Park. The last two sites are the southern-most of the northern sites and have been included to make the geometry more robust and to increase the number of observations per scan. Syowa will participate when the station is available. Because these sessions concentrate on the southern sites and do not use observing time to accurately tie these sites to far northern sites (as the Global Sessions do) they should yield a very accurate regional TRF around the South Pole. Syowa (Japan/Antarctica) are willing to participate in this experiment. The characteristics of this network have changed slightly due to more weigh of the southern part.

Syowa Anarctica:

These experiments were designed to strengthen the reference frame in the southern hemisphere, and to detect plate motion, in close collaboration with the JARE (Japanese Antarctic Research Expedition) project.


There are six bi-monthly coordinated astrometric/geodetic experiments each year that use the full 10-station VLBA plus up to 10 geodetic stations.

These experiments are being coordinated by the geodetic VLBI programs of three agencies: 1. USNO will perform repeated imaging and correction for source structure.; 2. NASA will analyze this data to determine a high accuracy terrestrial reference frame.; and 3. NRAO will use these sessions to provide a service to users who require high quality positions for small numbers of sources.


The Celestial Reference Frame (CRF) sessions are intended purely to provide astrometric observations useful in improving the current CRF, and in extending and densifying the CRF by observing "new" sources. The CRF sessions are scheduled 8 times this year.


The Survey sessions are two station networks intended purely to survey for southeren sources. The SURVEY sessions are scheduled 3 times this year.


The goal of the R&D sessions, as decided by the IVS Program Committee, is to compare the results of the IVS-R1 and the IVS-R4 sessions. The IVS-R4 sessions seem to be achieving better earth orientation results with a lower data rate (56 vs. 256). The R&D sessions are being scheduled to aide the analysts in understanding the 2002 results of the IVS-R1 and IVS-R4 sessions by scheduling sessions with a simular IVS-R4 network using the IVS-R1 observing mode. There are 10 sessions planned for 2003.