SETI@home scientists will have to wait for several weeks for the full analysis of the data collected during the reobservations (see Reobservations Report no. 2). But even while the observations are going on at Arecibo, they will already have a good idea if they have found something significant.
This is thanks to SERENDIP IV - the 168 million channel SETI spectrometer that piggy-backs on the Arecibo radio telescope throughout the year. As the giant dish scans the skies during the reobservations from March 18th through the 20th, SERENDIP IV will be processing the data in real time and telling to Dan Werthimer and his team if they are onto something interesting. These "real time" results will also help the SETI@home crew direct the reobservations more effectively. If a certain candidate signal seems particularly promising, they may decide to spend some extra time on it even at the expense of other candidates lower down on the priority scale.
SERENDIP IV has been operating at Arecibo since June of 1997, when it replaced the earlier 4 million channel spectrometer SERENDIP III. Like SETI@home, during most of the year it gathers its data from the SETI receiver at the base of the line feed. During the reobservations, however, it will be analyzing the data collected by the L Band receiver located in the Gregorian dome. That is the receiver that will be used by SETI@home scientists to revisit their most promising candidates.
In some ways, the SERENDIP IV search closely resembles SETI@home. Both projects look for signals near the hydrogen line at 1420 MHz, though SETI@home's unlimited computing power allows for a more sensitive analysis than is possible with SERENDIP. SERENDIP, however, scans a far wider frequency band around the hydrogen line - 100 MHz as against a mere 2.5 MHz for SETI@home. In fact, since both projects use the same receiver at Arecibo, the SETI@home data is simply the middle 2.5 MHz of the 100 MHz band analyzed by SERENDIP.
Unlike SETI@home, SERENDIP IV does not record the raw data collected by the Arecibo receiver. Instead, it processes it quickly by breaking it down to 168 million channels, each only 0.6 Hertz wide. Only significant radio pulses that rise substantially above the natural background noise of the spectrum are registered and referred for further analysis.
This makes SERENDIP IV ideally suited for real time analysis during the reobservations. While detailed analysis of the data will have to wait, SERENDIP IV will be on the spot, telling SETI scientists if they are onto something. If a true alien signal is out there among the 200 candidates, SERENDIP IV will most likely be the first to know about it.