Amir AlexanderJul 18, 2003

Analyzing the Reobservations

Many of you have probably been wondering by now whatever became of the mass of data gathered during SETI@home's Stellar Countdown back in March. At the time, as you may remember, SETI@home chief scientist Dan Werthimer and his team went back to Arecibo to reobserve the most promising candidate signals detected by the project so far. Unlike most of the year, when SETI@home piggy-backs on the regular operations of the telescope, this time the Werthimer's crew had the full use of the resources of the giant dish. They pointed it to whichever direction they wanted, using the most sophisticated receivers and recorders available. They came away with 24 hours worth of very high quality data, gathered from the most promising locations in the sky. It is time to catch up with the SETI@home team on how the analysis of all this information is coming along.

During the Stellar Countdown, the data collected by the telescope was inscribed on two separate recorders of differing sensitivity. The 2 bit recorder, which SETI@home uses throughout the year, and a highly sensitive 8 bit recorder. Because of their different format, the data collected by each of these instruments must be analyzed differently.

Processing the data from the 8 bit data recorder is no simple matter. Because SETI@home had never before used this instrument, there are no computer programs in place ready to perform the necessary analysis. The standard SETI@home program, which is installed on all users' computers, was not designed to process this type of information. New processing programs for this data must be designed, and SETI@home Project Director David Anderson is working hard on the project. Along with other members of the SETI@home team he is devising a new distributed computing system designed specifically to deal with the data from the 8 bit recorder. The system, however, will not be ready for several more months, and in the meantime Anderson, Werthimer and their crew are concentrating on the data from the less sensitive 2 bit recorder.

This instrument presented an easier challenge to SETI@home scientists. All normal SETI@home work units are produced from the information collected by the 2 bit recorder, and the SETI@home crew could therefore process the recordings from the reobservations data in the same manner they process information recorded throughout the year. The data was carved up into standard work units, and sent out to millions of users around the world for processing. They analyzed the data and then sent back their results to SETI@home headquarters in Berkeley, just as they do with any ordinary work unit.

When this process was completed last month the SETI@home team turned to the next stage of their analysis. The processing by SETI@home users had turned up a host of potential candidate signals, which must now be correlated with the candidates detected previously. Each new candidate will be given a score based on several factors including its strength, origin, and - most importantly - whether it had been detected previously. They will, in other words, be processed and ranked in exactly the same way as were the candidate signals before the Stellar Countdown, only this time - with additional data from the targeted reobservations. The SETI@home team is particularly interested to find out whether the score and ranking of any of the 166 candidate signals revisited during the Countdown had increased as a result of the reobservations. Such a candidate would certainly be the object of much further study.

And so, the hard work of analyzing the results of the Stellar Countdown continues apace. It's taking somewhat longer than hoped, but once it is completed SETI scientists will be that much closer to answering that persistent question: is anybody out there?

We promise to keep you posted.

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