Can someone explain what the visualizer is showing in simple terms?


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Zan Sullivan-Wilson
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Message 1092553 - Posted: 2 Apr 2011, 7:16:43 UTC

I've read through the information posted in the "about" section, but I still don't seem to get all of it. I would love it if you guys could fill in some gaps for me.

On the top left pane of the visualizer there is a bar graph/histogram, but the axes are not labeled. I'm pretty sure the y-axis shows signal power. But I'm not sure if the x-axis refers to time or frequency. Also, how does the top left pane relate to the 3D pane on the bottom?

From the "about" section of this website it seems like time is on the x-axis of the top left pane. When it talks about pulses and triplets it shows spikes spread out along the x-axis (if pulses that are repeated in time are spread out over the x-axis, it seems to imply that time is on the x-axis). However, in the 3D graph on the bottom it shows frequency on the x-axis. Is the 3D graph showing the same data as the top left pane?

Thanks!

Profile Johnney Guinness
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Message 1092574 - Posted: 2 Apr 2011, 9:27:45 UTC - in response to Message 1092553.
Last modified: 2 Apr 2011, 9:30:46 UTC


On the top left pane of the visualizer there is a bar graph/histogram, but the axes are not labeled. I'm pretty sure the y-axis shows signal power. But I'm not sure if the x-axis refers to time or frequency. Also, how does the top left pane relate to the 3D pane on the bottom?

The x-axis does refer to time! The SETI@home uses a computer algorithm called Fast Fourier transform to analyze the signal data looking for sequences that don't happen naturally. See wikipedia; http://en.wikipedia.org/wiki/Fast_Fourier_transform


From the "about" section of this website it seems like time is on the x-axis of the top left pane. When it talks about pulses and triplets it shows spikes spread out along the x-axis (if pulses that are repeated in time are spread out over the x-axis, it seems to imply that time is on the x-axis). However, in the 3D graph on the bottom it shows frequency on the x-axis. Is the 3D graph showing the same data as the top left pane?

Thanks!

Its 3D, remember time is constant so time is on the x-axis. If you watch the screensaver, you will see it "stacking" the layers one in front of the other to form the 3D effect. But really its 2D data, its just stacking in 3D to make it look cool and attract more users. The screensaver looks cool but its just nice graphics, don't read into it too much :)

John.
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Zan Sullivan-Wilson
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Message 1092739 - Posted: 2 Apr 2011, 19:19:33 UTC - in response to Message 1092574.

Thanks for the response. That makes sense now. Just a couple more questions if you don't mind. :)

Each histogram in the top left is 2D data showing a range of signal powers over time. So each histogram represents a time range at a single frequency. But I also know that data is analyzed over a range of frequencies. So let's say I see a histogram that represents data at frequency x. Once my computer finishes analyzing that histogram a new one pops up. Is that new histogram at the same time range as the first histogram, just at frequency x+10kHz? I'm guessing that once a single time range is analyzed at all frequencies (filling up that 3D graph entirely), then it moves on to the next set of histograms at the next time range. Am I on the right track?

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Message 1092854 - Posted: 3 Apr 2011, 1:24:45 UTC - in response to Message 1092739.
Last modified: 3 Apr 2011, 1:27:43 UTC

Zan,
The SETI@home algorithm is only searching for signals at one frequency. Its called the Hydrogen line, its a 1420MHz; http://en.wikipedia.org/wiki/Hydrogen_line. This is natural resonant frequency for atomic hydrogen. So any info that is displayed in the screensaver graphics is at that frequency. But it looks for different things they call Spikes, Gaussians, Pulses and Triplets. So that histogram you describe is probably displaying stuff like that.

Sullivan....Hmmmmm.....Won't take me too many guesses too guess where your family roots are from...LOL

John in Ireland.
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Zan Sullivan-Wilson
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Message 1093008 - Posted: 3 Apr 2011, 17:13:45 UTC - in response to Message 1092854.

Thanks for replying again. You're right on about the Sullivan! Although sadly, I've never visited. Someday I need to make the trek.

I think there must be range in the frequency. The "about" section mentions that there will likely be a doppler effect in the signal if it is coming from a rotating planet and earth itself is rotating. So it is centered on the hydrogen line but it looks like a range of frequencies around it are also analyzed. Here is a link to where it talks about this: http://seticlassic.ssl.berkeley.edu/about_seti/about_seti_at_home_2.html

I wish this website had a better explanation of the graphics. Or at least labeled the axes and data better. Oh well, its still fun to contribute!

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Message 1093031 - Posted: 3 Apr 2011, 18:21:17 UTC - in response to Message 1093008.
Last modified: 3 Apr 2011, 18:22:23 UTC

Zan,
Ahhhh.... I found a full page of information for you!! Feast your eyes on this info;
http://www.boinc-wiki.info/Screen_Saver_&_Graphics_Display_-_SETI@Home
Everything you need to know about the screensaver.

That will keep you busy for a while. Do make the trip to your ancestral home in the coming years if time and money allow Zan.

John
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Zan Sullivan-Wilson
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Message 1093179 - Posted: 4 Apr 2011, 2:05:18 UTC - in response to Message 1093031.

Good find! That answers a lot of questions. Thanks for the help.

Message boards : SETI@home Science : Can someone explain what the visualizer is showing in simple terms?

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