1. What does SETI@home do? Mini-project for CSE 260 Qian Peng 15 November 2001 Ref. http://setiathome.ssl.berkeley.edu/

2. 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.

3. 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

4. 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

5. 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  2 fit to Gaussian (telescope beam profile) Search for triplets (three evenly spaced signals) Search for pulses (lots of equally spaced weak signals)

6. 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)

7. 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.

8. E.T.I. ?!