Document on Argus

A: Argus is a project to design radio telescopes that can observe the entire sky, all the time. This can be done using large, planar arrays of antenna elements with hemispherical patterns. Each antenna element has its own dedicated receiver, and the outputs of all receivers are combined in a computer to form radio images of the sky. This is in contrast to traditional radio telescopes, which are usually big paraboloidal reflectors (dishes), which can see only a very tiny portion of the sky at a time.

Argus was conceived by Bob Dixon, Assistant Director of the OSU Radio Observatory (Big Ear), in the early 1980's.

Q: Why Build Argus?

A: For nearly 30 years Big Ear was dedicated to the Search for Extra-Terrestial Intelligence (SETI), which involved searching the sky for weak radio signals. A big problem for SETI is that traditional radio telescopes (like Big Ear) have a narrow field-of-view. This is compounded by the fact that one does not know where in the sky to search. Thus, traditional SETI surveys are slow, and are likely to miss transient or one-time signals.

Bob Dixon realized in the early 1980's that an alternative, possibly better strategy is to look at the entire sky, all the time. This approach is currently limited by computer power; however, the amount of computer power available per dollar is increasing so fast that we do not expect this to remain a limitation for long.

In the last few years, it has become apparent that Argus technology has other uses as well. In recent years, it has become clear that the radio sky is more dynamic than once thought. For example, gamma ray bursts (GRB) -- currently of great interest to astronomers - are sometimes accompanied by strong radio signals, but only for a short time. It is unlikely that a traditional radio telescope anywhere in the world is looking at the right place when this happens. It is now suspected that there are many interesting natural, transient phenomena currently unnoticed simply because astronomers can only monitor a tiny fraction of the sky at any time. The Argus strategy is a practical means to detect these sources.

Another use for Argus technology, practical at this very moment, is to detect and track radio frequency interference from sources on the ground and from satellites in space. This information can then be used to set observing schedules for traditional radio telescopes, used in both mainstream radio astronomy and SETI, to avoid the interference.

Q: What is the current state of Argus development at OSU?

A: Currently, we are constructing a system with 8 antenna elements on the West Campus of OSU. This stage of the system should be fully operational within a few months. The antennas have been installed, and first few receivers have been constructed and tested. As part of the construction, we have tested various sections of the system. For example, we can now detect and track satellites as they move through the sky. We have done this at both edges of the frequency band of interest; in particular, 436 MHz and 1575 MHz. However, we will not be able to form images or deal with local RFI effectively until all 8 antenna/receiver signal chains are on line.

We currently have funding to build a system of 64 antennas. This will be mainly a process of repeating the initial 8-element system seven more times, and should go relatively quickly. We plan to have the 64-element system operational by Spring 2001.

It should be emphasized that Argus is unlike any radio telescope ever built. As a result, we have had to figure out a great deal of new theory and design rules for the first time. Much of the past two years has been spent not in building Argus per se, but rather in working out the theory and design methodology. For example, we have developed:

• A new broadband antenna element
• A novel wideband digital receiver with wide-tuning range
• Algorithms for calibrating the system using both locally-generated and distant sources of opportunity (e.g. satellites).
• Algorithms for detecting and suppressing RFI

Much of this has applications to radio astronomy as well as SETI, and we currently collaborate with radio astronomers in the US, Australia, and the Netherlands who have applications for this technology.

Q: Is Argus doing SETI?

A: At this moment, no. SETI requires very high sensitivity and an observing site with low radio frequency interfence (RFI). Currently, this is only practical with large dishes in remote locations; for example, Arecibo in Puerto Rico and Parkes in Australia. When the current version of Argus is completed, it's sensitivity will be less than that of a backyard satellite TV system. Furthermore, the RFI situation at the current location (the West Campus of OSU) is far too noisy for practical SETI work.

So why bother? The main goal of the current Argus project is to learn how to build practical omnidirectional radio telescopes. Based on what we learn in the next few years, a larger system suitable for practical SETI work may be built in rural areas where the RFI situation is better. However, much needs to be learned about the basic technology, which is why the first system is being implemented here at OSU.

Q: What will the 8- (ultimately, 64-) element Argus be able to do?

A: The 8/64-element system will be able to analyze a 3-MHz chunk of the radio spectrum from anywhere between 400 MHz and 2000 MHz, imaging the entire sky at a time. Despite the limitations, the system will easily detect the strongest interesting natural astronomical radio sources, such as the center of the galaxy (Sagittarius A) and several interesting supernova remnants. Argus should be able to detect a few pulsars as well. It will simultaneously be able to resolve interesting spectral features, such as the 1420-MHz spectral line associated with Hydrogen, which can be used to measure the relative velocity of astronomical objects. The purpose of these observations will be mainly to determine the limits of sensitivity of the system, since natural sources make excellent benchmarks. However, it will also be the first time such data have ever been captured for the entire sky at once.

Despite it's initial limitations, Argus will be capable of detecting certain classes of SETI candidate signals. In particular, any signal which is strong enough to be detected by a 1-meter dish with a few seconds of integration will also be detectable by the 64-element Argus. The difference is, of course, that Argus will have this sensitivity over the entire sky. Thus, Argus may detect strong signals which go unnoticed simply because no other radio telescope is looking in the right place at the right time.

The system will also be well-suited to the detection and tracking of satellites transmitting between 400 MHz and 2000 MHz. Satellites represent a perpetual headache for radio astronomers around the world. This is because reliable information on many of the troublesome satellites is not available to the public. Using Argus, however, we can periodically make an inventory of transmissions from orbit, which can then be analyzed to determine orbital parameters and possibly identify the satellite. Radio astronomers can then schedule their observations to minimize the impact of these satellites.

Q: Who is involved in the Argus project at OSU?

A: The key players are:

• Dr. Steven W. Ellingson, Senior Research Associate, OSU ElectroScience Laboratory (ESL) (Part of the Dept. of Electrical Engineering). Dr. Ellingson leads a team of researchers and students who are developing the 8/64-element Argus system described above.
• Dr. Robert S. Dixon, Chief Research Engineer, Office of the CIO, OSU. (Former Assistant Director of the OSU Radio Observatory, Big Ear)
• Dr. Philip E. Barnhart, Professor Emeritus of Physics and Astronomy, Otterbein College; Coordinator of NAAPO, a group of local volunteers who previously supported operations at Big Ear and now are working on various aspects of Argus.

Q: Who is supporting the Argus project at OSU?

A: Most of the support for Argus comes from the SETI Institute (www.seti.org), which in turn is supported primarily by private donations. OSU provides laboratory space, some of which is shared by several other projects. Significant support also comes from local volunteers (www.bigear.org), who contribute their own time and expertise, as well as coordinating donations of money and equipment from local businesses and private citizens.

Q: How can I learn more and keep track of the Argus Project?

A: The following web sites are recommended:

• OSU ESL RF Systems Engineering Group (http://esl.eng.ohio-state.edu/rfse)
• Big Ear Volunteer Group (http://www.bigear.org)

Q: Is there any way that the public can get involved?

A: The Big Ear volunteer group is always looking for motivated local volunteers; especially those with technical skills to offer. Donations of money and equipment are also appreciated. Click on the FEEDBACK link below for details.

Checks made out to NAAPO/Otterbein may be sent to:

     NAAPO
     C/o Dr. Philip E. Barnhart
     4655 Indian Ct
     Westerville,  OH  43082