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CONT11 two week continuous Geodetic VLBI 2011/09/15 - 2011/09/29


Every three years a major campaign is carried out to test the latest advances in geodetic VLBI - precision position determination using astronomical radio sources. 'VLBI' is short for Very Long Baseline Interferometry, which means multiple radio telescopes observe the same source at the same time and the data from each pair of telescopes are combined to produce an interference pattern which depends on their position on the Earth.

The official webpage on CONT11 provides detail on the science that will be obtained.

The CONT11 campaign comprises 15 day-long experiments. Each experiment consists of many short observations of the distant quasars that form the 'reference beacons' in space for determining the positions of the radio telescopes involved to high precision.

The experiment on September 15, for example, had the HartRAO 26m antenna carrying out 324 observations, providing 1.83 Terabytes of data. Thirty three percent of the time was spent acquiring data while tracking on the radio sources, 53% was spent slewing from source to source across the sky, 4% was spent calibrating and only 9% was idle time - the lowest for any of the participating radio telescopes.

The IVS live website provides real-time view of what is happening in the world of geodetic VLBI.

The CONT11 experiment was successfully completed on Friday 2011/09/29 at 02h00 local time. Only one of the daily scheduled hour long maintenance periods was needed for the HartRAO telescope, to fix an intermittent wiring problem. A total of 2.5 hours of data recording was lost to that and other minor problems, from 360 hours of observing.

The participating telescopes are shown in the map below.

map
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The 26m HartRAO telescope is the only VLBI-capable one in Africa. It has mutual visibility with all the other telescopes except Kokee Park on Hawaii, which is on almost the opposite side of the Earth. 'Mutual visibility' means that the telescopes can observe the same radio source at the same time - an essential requirement for VLBI. The telescope shown at Warkworth, New Zealand dropped out owing to technical reasons. (Map courtesy of the International VLBI Service for Geodesy and Astrometry).

Marisa
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Geodetic VLBI operations controller Marisa Nickola checks the progress of the VLBI on the first morning of CONT11, seated at the VLBI control computer. The VLBI recording systems are visible behind her.

instruments
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The HartRAO 26m telescope is seen left of centre at 09h30 SAST slewing west from radio source 1156+295 to 0727-115. In the left background is the 15m antenna built as a prototype for the Karoo Array Telescope. It is being converted to be able also to do geodetic VLBI. Its advantage over the 26m telescope for this is its faster slew rate. Right of centre is another geodetic instrument, the NASA MOBLAS-6 Satellite Laser Ranger, seen ranging to the LAGEOS satellite. The SLR data are sent to the International Laser Ranging Service. To its right is the roll-off observatory containing a new laser ranger under development. In the left foreground is the small circular Global Positioning System basestation antenna that supplies data to the International Global Navigation Satellite System Service. These precise position measuring systems are co-located with the radio telescope to provide cross-referencing.

spectrum
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Inside the MOBLAS-6 SLR control van, Klaas Ramaoka is seen in the foreground optimising the tracking of the LAGEOS satellite. SLR Technical Manager Lusanda Ntsele, standing behind him, checks the SLR equipment.

spectrum
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HartRAO electronics technician and VLBI operator Lerato Masongwa checks the air temperature and weather around the radio telescopes.

spectrum
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Lerato notes the weather details at the VLBI terminal. Lerato took the first night shift, and started up the VLBI at HartRAO at 02h00 local time on September 15.

spectrum
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The HartRAO geodetic VLBI operations team. VLBI Manager Jonathan Quick (foreground) briefs (from the left) Marisa Nickola, Ronnie Myataza, Lerato Masongwa and Jacques Grobler.