• This diagram illustrates the major components of LOFAR. Radiation is collected by wideband dipole antennas above a ground screen, and signals are immediately digitized. The antennas are clustered together in groups of approximately 100, forming "stations." An artist's impression of one station, located in a generic desert site, is shown (courtesy of ASTRON, Netherlands). Stations are connected by high bandwidth fiber optic lines, and may be arranged in a multiarmed log-spiral configuration. Signals are fed to a central processing facility featuring massive and highly parallel computational capacity. The array has no moving parts, and will be remotely operated over the internet.

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Haystack, CSR involved in major new digital telescope development


The development of a powerful new radio telescope for radio astronomy and for probing the solar terrestrial environment is the focus of a scientific and technical meeting at MIT's Haystack Observatory in Westford this week.

The Low Frequency Array (LOFAR), scheduled to be completed in 2006, will be the first major telescope that is fully digital. Spread over 240 miles, it will have no moving parts, as well as extreme frequency and pointing agility and the capability of observing in several directions at once. The project is an international collaboration among MIT's NEROC (Northeast Radio Observatory Corp.) Haystack Observatory, MIT's Center for Space Research, the Naval Research Laboratory in Washington, D.C., and the Netherlands Foundation for Research Astronomy (ASTRON).

"LOFAR's development and array design will be driven by radio astronomy goals to achieve a collecting area of one square kilometer at 15 MHz, and arc-second angular resolution at 150 MHz," said Colin Lonsdale, Haystack's principal investigator for the LOFAR project. "An important goal of this week's meeting is to introduce LOFAR to the scientific community, especially within the U.S., and to further define and expand the scientific goals." Around 100 scientists and engineers from 40 institutions in Europe and the United States are participating in the meeting, which runs from Oct. 15-19.

Initial funding for the design phase includes a $2 million grant to MIT from the National Science Foundation's Information Technology Research (ITR) initiative, with additional funding through ASTRON and the Naval Research Laboratory. The final cost of the project is estimated to be between $50 million and $75 million.

When completed, the array will have 13,000 dipole antennas operating in the 10-240 MHz frequency range clustered in roughly 100 stations spread over a region 400 km (240 miles) in diameter.

Connected through fiber-optical links, the interferometric array will be capable of digitally forming multiple simultaneous beams that can be electronically steered, will possess extreme frequency agility, and will provide a flexible system for distributed control, signal processing, monitoring and remote operation. Potential sites for LOFAR in the southwestern United States, western Australia and the Netherlands are being evaluated.

Professor of Physics Jacqueline Hewitt is one of the leaders on the project and is looking forward to the new scientific results. "One of the most exciting prospects for LOFAR is that we will be able to make pictures of clumpy clouds of hydrogen gas in the very early universe, right at the moment when the first stars and galaxies were forming and starting to shine. We cannot see these stars and galaxies directly, but by studying the hydrogen we can learn a great deal about how the universe was behaving during this key phase of its evolution," she said.

"Another unique capability of LOFAR is its ability to look in many directions at once, which makes it ideal for observing short-lived radio sources that may flare up for a few seconds or minutes then die away again," Hewitt said. "Such transient sources are rarely seen by conventional telescopes but are expected to be plentiful in the LOFAR sky, signposting the existence of a variety of exotic objects--some of which may be unknown to science today."

Not only will Haystack's radio astronomers benefit from the development of LOFAR, but the instrument also will be a powerful new tool for solar and ionospheric studies. Given its low frequencies of operation, an adaptive phase-based calibration of the instrument will be required to compensate for ionospheric delays with extremely high precision using astronomical radio sources observed along many lines of sight to the stations.

These observations will enable the application of radio tomographic techniques to construct a three-dimensional view of ionospheric structure above the array with exquisite detail and precision. There also may be opportunities for detecting and tracking coronal mass ejections from the sun through interplanetary scintillations and for passive radar observations using FM radio stations as transmitters of opportunity.

A version of this article appeared in MIT Tech Talk on October 17, 2001.


Topics: Space, astronomy and planetary science

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