More space at the CSIR

Johannesburg, 26 May 2008

The Council for Scientific and Industrial Research`s Hartebeeshoek radio observatory (Hartrao) last week took part in the first real-time broadband-based electronic Very Long Baseline Interferometry (e-VLBI) space scan to simultaneously use telescopes in Africa, Europe, North America and South America.

e-VLBI is a technique by which remotely located radio telescopes observe the same region of sky simultaneously. Data from each telescope is sampled and sent to a central processor, in real-time via broadband.

The e-VLBI data centre, located in Dwingeloo, in the Netherlands, contains a purpose-built supercomputer that decodes, aligns and correlates the data for every possible pair of telescopes. It can generate images of cosmic radio sources with up to a hundred times better resolution than images from the best optical telescopes.

Traditional VLBI relies on storing data on high-capacity disk arrays that are shipped to the correlator. Huib Jan van Langevelde, director of the Joint Institute for VBLI in Europe (JIVE), says the elimination of the long delay between observations, correlation and subsequent data reduction, electronic real-time VLBI enables astronomers to respond rapidly to so-called transient phenomena, like supernova explosions and gamma ray bursts.

The development of e-VLBI also holds the potential for deeper and more sensitive observations by taking advantage of the explosive growth of Internet bandwidth. This will ensure the JIVE network, that now also includes Hartrao, "will remain both competitive and complementary to next-generation astronomical observatories", including the proposed Square Kilometre Array for which SA is bidding.

Van Langevelde says Thursday`s observation of a distant quasar (a type of star) numbered 3C454.3 linked Hartebeesthoek with Arecibo, in Puerto Rico, Effelsberg, in Germany, the Transportable Integrated Geodetic Observatory, in Chile, in addition to Medicina, in Italy, Onsala, in Sweden, and Westerbork, in the Netherlands.

"These results are very significant for the advance of radio astronomy; it shows not only that telescopes of the future can be developed in worldwide collaboration, but that they can also be operated as truly global instruments," says Van Langevelde.

Technical challenges

JIVE head of technical operations and R&D Arpad Szomoru says connecting telescopes across the distances involved posed some unique challenges. "Transport via TCP/IP is not suitable, but the use of UDP can cause serious disturbances in connectivity for other users.

"For this demo we have applied a number of methods, like the use of 1Gbps light paths with guaranteed bandwidth, VLANs and plain IP-routed connections. The success of this test demonstrates that global e-VLBI has become an operational reality."

Szomoru says data from the seven telescopes was routed across a number of networks, including AtlanticWave, AMPATH, Centennial, DFN, G'EANT2, Netherlight, NGIX, RedCLARA, Reuna, SANReN, StarLight and Tenet.

JIVE is presently running a project to connect 16 of the world`s most powerful radio telescopes to the data correlator at Dwingeloo, with an aggregate data flow of up to 16Gbps by September next year.