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What does SETI@home do?. Mini-project for CSE 260 Qian Peng 15 November 2001 Ref. http://setiathome.ssl.berkeley.edu/. Data Source. Sky survey conducted by National Astronomy and Ionospheric Center’s 305 meter radio telescope in Arecibo, Puerto Rico.
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What does SETI@home do? Mini-project for CSE 260 Qian Peng 15 November 2001 Ref. http://setiathome.ssl.berkeley.edu/
Data Source • Sky survey conducted by National Astronomy and Ionospheric Center’s 305 meter radio telescope in Arecibo, Puerto Rico. • Covers 28% of sky, most sky will be observed two or three times during the course of the project. • Recorded on 35GB DLT tape. Complete survey requires 1100 types, total of 39 TB data. • Tapes are mailed to Berkeley.
What to Look for • Extraterrestrial intelligence signals are of unknown bandwidth and time scale • Wide band (unlikely), narrow band (most likely) • Both continuous and pulsed signals are possible • Need to reject local radio frequency interference • Local source tends to be constant while sky drifts past the telescope (12 seconds for a target to cross the focus) • Look for 12-second Gaussian signal • Need to correct Doppler shift (frequency change) caused by relative motion
Distributing Data • Embarrassingly parallel • Frequency bands are independent of one another • An observation of one portion of the sky is independent of an observation of another part • Work unit of 107 sec. 10 kHz data sent to client • Survey covers 2.5 MHz data, centered at 1420 MHz • Broken into 256 blocks, each 9766 Hz wide • Need to record at 20 kbps for signal up to 10 kHz • 20kpbs x 107 s. + additional info -> 340 KB each unit
2.4 to 3.8 Tflops for Each Work Unit • Baseline smoothing to reject broadband noise • For Doppler shift rates from -50Hz/s to 50Hz/s, de-chirp data, for bandwidth resolutions from 0.075 to1220 Hz in 2X steps • FFT to generate time-ordered power spectra • Search for short duration signals above a threshold • For each frequency • c2 fit to Gaussian (telescope beam profile) • Search for triplets (three evenly spaced signals) • Search for pulses (lots of equally spaced weak signals)
SETI@home Server Side • 4 splitter workstations to divide 2.5MHz data into 256 sub-bands using FFT & inverse FFT, and form work units. Temporary storage. • 3 Sun Enterprise 450 servers • User database (work units completed, membership) • Science database • time, sky coordinates, frequency for each work unit • Parameters of potential signals detected by clients • Work unit storage (handle distribution, store results)
What Happens to Qualified Signals • Each work unit sent to multiple clients, cross-check results • Most signals rejected as RFI or test signals based on a large database of known RFI sources • Search remaining data for multiple detection • Follow up with dedicated observation • Have another team cross-check (different telescope, etc), then interferometry measurements.
