e-VLBI Measures Earth and Sky

October 19, 2005

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by Katie Yurkewicz, Science Grid This Week

The technique of Very Long Baseline Interferometry has been used since the late 1960s by astronomers to make detailed images of distant radio-emitting objects in the universe, and by geoscientists to precisely measure the dynamics of the Earth. This well-established technique uses an array of independent antennas, scattered over the surface of the earth and synchronized with atomic clocks, to make simultaneous observations. With the use of global multi-gigabit optical networks, VLBI may be poised for a major upgrade.

"VLBI was originally developed by radio astronomers to make high- resolution measurements of quasars," said Alan Whitney from the Massachusetts Institute of Technology's Haystack Observatory. "In some VLBI observations, scientists can make high-resolution images of a distant radio source equivalent to discerning the dimples on a golf ball 3,000 miles away. The distances between the antennas can also be measured to an accuracy of a few millimeters anywhere on the surface of the Earth. This allows geophysicists and geologists to make direct measurements of the motion of the tectonic plates, as well as extremely accurate measurements of the motion of the Earth in space."

Traditionally, VLBI data from up to 20 antennas are simultaneously recorded to magnetic tapes or disks and physically shipped to a central location, where a specialized processor called a correlator searches for common signals in the data. High-speed networks directly linking the antennas with the correlator would allow scientists to view the correlated signals very soon after they are recorded and adjust their observations accordingly. A networked e-VLBI system would also have the potential to move data at much higher rates, dramatically increasing the technique's sensitivity.

"e-VLBI offers scientists two important advantages: a quick look at their results to refine their observation strategy in near-real-time; and the potential to increase data rates well beyond what they are now," explained Whitney. "Increased data rates will increase the sensitivity of the observations, which will allow scientists to look at broader selection of distant objects in the universe, and to make more precise measurements of the dynamics of the Earth's motion in space."

While widely available 10 or 100 gigabit networks are still some years away, the e-VLBI team led by MIT demonstrated the technique's possibilities at iGrid 2005 in September. High-speed optical networks transferred data in real time from antennas in Westford, Massachusetts; Greenbelt, Maryland; and Onsala, Sweden at 512 Mbps per station directly to the correlator at MIT's Haystack Observatory. The processed results from the quasar observation were then streamed to the conference floor in San Diego. Direct high-speed optical connections were dynamically created, configured and then destroyed using the DRAGON (Dynamic Resource Allocation over GMPLS Optical Networks) control plane and Internet2 HOPI (Hybrid Optical and Packet Infrastructure) network.

The e-VLBI team, led by MIT, has been working for about 3 years to integrate VLBI with these new networking technologies, and similar efforts are underway in Europe, Japan and Australia.

The e-VLBI iGRID demonstration was supported by MIT, the National Science Foundation, University of Maryland, Mid-Atlantic Crossroads, NASA, MIT Lincoln Labs, Internet2, StarLight, University of Manchester, UKLight, SURFnet, JIVE, ASTRON, Onsala Space Observatory, SUNET, ESLEA, NORDUnet, NICT and JGN2.

For information on the MIT Haystack Observatory, see: