SETI@home Plans
SETI@home Plans |
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Last updated: (24 Apr 2008 21:48:30 UTC)
We continually work on several long term projects which improve the power and scientific output of SETI@home. Recent accomplishments on this front as well as future plans are noted below.
This SETI@home Enhanced application was released to the public in May 2006. Because Moore's law has been continually increasing the computing power of our volunteers, we developed this new SETI@home application with increased sensitivity. The original SETI@home (a.k.a. SETI@home "Classic") stepped coarsely through doppler drift rates. Because of this, there was a possibility of a Gaussian shaped or pulsed signal drifting out of a frequency bin during the duration of the analysis. These signals would be recovered later when the analysis is performed at lower frequency resolution. However, because more noise is included in the analysis performed at lower resolution, it decreases our sensitivity to such signals by a factor of two. In the early days there wasn't enough computing power available to perform this full analysis at high resolution.
We developed a high speed data recording system to take advantage of the new 7 beam ALFA receiver at Arecibo. Conceptually similar to the SETI@home I data recorder, it was redesigned and implemented with a number of improvements.
It is capable of taking data much faster than the original SETI@home I recorder. While maintaining the sampling rate and instantaneous bandwidth of the old recorder, the new system is more than capable of taking data from all 7 beams (better sky coverage) at both linear polarizations (more sensitivity).
The multi-beam recorder is able to monitor the pointing coordinates of the telescope. When the telescope is tracking a point on the sky, the frequency band being recorded will be periodically changed. This gives us greater frequency coverage rather than redundant coverage of just one part of the spectrum.
The new recorder will also monitor the receiver state and when the ALFA receiver is off (for example, when AO is transmitting), data acquisition is idled in order to conserve I/O resources.
The data recorder consists of front end hardware, a host computer, and an array of high speed disks. The front end receives the analog signal from the receiver, converts it to a lower frequency and digitizes it. The host computer receives the digital data, collates it with timing and pointing data and writes it to disk, using a separate disk array as a buffer. It also makes decisions on whether or not to take data and controls frequency stepping.
Since the raw data is organized in a different manner, a new SETI@home application was created to analyze data in this new format. This application went public in the fall of 2007. We have been strictly sending out multi-beam data to our users ever since.
After applications return signals they are validated and stored in our master database. The goal of SETI is to find similar signals that appear at the same frequencies and points in the sky, but at different times. With a database containing billions of signals, this is a rather large task to do all at once. In the past we had no choice - we didn't have enough resources to create a real-time data analysis pipeline that wouldn't clobber our entire project. In fact, as of August 2005 we still had over 50 tapes' worth of data that had yet to be validated and put into our master science database.
But now we are using BOINC, which has the ability to hand us reduced data for final analysis within minutes of client completion. Plus our new master science database is on a machine with more memory and faster disk throughput. For the first time since its inception, SETI@home has the potential for finding the most interesting repeating signals soon after these signals enter the database. We hope to have daily reports updated with the current "best" results when this system is put into place.
Development is currently very active on the NTPCKR and we will have a look under the hood in a upcoming newsletter. In the meantime, you can read more about our original near time persistency checker plans in this older news story.
The current SETI@home application looks for signals that are narrow in frequency, but have long duration. That's one way that an extraterrestrial civilization can send a signal that stands up above the radio background noise. Another possibility is that they could put a lot of power into a short duration pulsed signal that has a wide bandwidth. As such a pulse travels through interstellar space, interactions with interstellar matter slow down low frequencies relative to high frequencies in a process called dispersion. This dispersion spreads the pulse out over time. If we know how much dispersion a pulse has experienced, we can correct for this effect. For an extraterrestrial signal we won't know how much interstellar matter the signal interacted with on its journey, therefore we have to try every possible dispersion measure. That takes a lot of computing time.
Astropulse is a SETI@home application that uses coherent dedispersion to search for pulsed signals. In addition to extraterrestrial signals we might see signs of evaporating black holes or discover new pulsars. You can read more about Astropulse here .
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