Re: SETI like tass project

[Doug Welch <welch@physics.mcmaster.ca>]

Chris,

Sadly, an FFT in not appropriate for non-uniformly
sampled data. DFT's are much slower!

Cheers,
Doug

On Tue, 29 Jan 2002, Chris Albertson wrote:

> Even a 1000 point FFT is fast to compute compared to the
> time to transmit the 1000 points in both directions.
> 
> Search problems typically take CPU time.  Here is one:
> Let's say you have a few thousand observation records of the
> form (ra, dec, mag) and they are all very close in ra,dec.
> you want to know if you are seeing one object or N unresolved
> objects.  Maybe they are at the limit and resolve some nights
> and not others or maybe in one color but not in the other
> color.  Doing this right could be a very large search space.
> 
> What you'd do is have all the observations in a database and
> the SETI-Like clients would querry the database for a few
> square minutes of data, work on the data.  The client would
> divide up all the observations into stacks for object "A",
> "B", "C" and "A+B blended", "C+B blend" and so on using total
> flux and color index.  It's not an easy problem and you need
> to keep re-computing as you add more observations.
> 
> A realated problem we found with the Mk III was that the database
> tends to fill up with "noise" stuff that was detected once and
> never again.  Someone or some system need to contiouly look for
> objects seen only once in areas of the sky that were imaged
> multiple times.  This isn't a SETI problem in of itself because
> the DBMS can turn this up directly but someone has to figure out
> if these "seen once" events are real.  We know that they are
> common but a very few may be real.
> 
> 
> --- Doug Welch <welch@physics.mcmaster.ca> wrote:
> > 
> > I fully agree with Dirk's assessment. A time-series analysis
> > for many hundreds or thousands of points per object to high
> > frequencies can be quite CPU-consuming. Obviously, the sampling
> > needs to be appropriate to the task.
> > 
> > Cheers,
> > Doug
> > 
> > On Tue, 29 Jan 2002, Dirk Terrell wrote:
> > 
> > > On Tue, 29 Jan 2002 16:02:52 -0600, Tom Droege wrote:
> > > 
> > > >Let's discuss how we might do this.
> > > 
> > > I have a bit of experience in this area. I do the OS/2 port of the
> > S@H
> > > client and I have written a distributed computing client/server
> > project
> > > called SwiftPC that does solar system dynamics calculations.
> > > 
> > > The TASS data situation is probably quite a bit different from S@H
> > or
> > > SwiftPC in that the CPU need per megabyte of data is much lower.
> > That
> > > is, we are probably bandwidth limited rather than CPU limited with
> > this
> > > problem. The time required to download data will be larger than the
> > > processing time. That's not the kind of problem that lends itself
> > to
> > > distributed computing. The way to tackle this problem is, as you
> > > suggest, to have a few machines chew through it. In the long run, I
> > > think you want to process the data as they are taken, eliminating
> > the
> > > need to do a huge amount all at once. Now, where it might get
> > > interesting is if you have a bunch of (date,magnitude) pairs for
> > huge
> > > numbers of objects and you want to do a variability analysis. That
> > > might be more appropriate for a distributed computing project.
> > > 
> > > Dirk
> > > 
> > > 
> > > 
> > 
> > ==============================================================
> >  Douglas L Welch     | Office/voicemail (905) 525-9140 x23186  
> >  Physics & Astronomy | FAX              (905) 546-1252 
> >  McMaster University | 
> >  Hamilton, Ontario   | 
> >  Canada L8S 4M1      | E-mail       welch@physics.mcmaster.ca
> > ==============================================================
> > 
> > 
> 
> 
> =====
> Chris Albertson 
>   Home:   310-376-1029  chrisalbertson90278@yahoo.com
>   Cell:   310-990-7550
>   Office: 310-336-5189  Christopher.J.Albertson@aero.org
> 
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==============================================================
 Douglas L Welch     | Office/voicemail (905) 525-9140 x23186  
 Physics & Astronomy | FAX              (905) 546-1252 
 McMaster University | 
 Hamilton, Ontario   | 
 Canada L8S 4M1      | E-mail       welch@physics.mcmaster.ca
==============================================================