[daip] Request for experimental Task

[Leonia Kogan]

Frazer,

I looked at the UVAVG codes yesterday (Thursday) and found I'll be able to 
create the private version of UVAVG which can average the UVdata along a 
huge time interval and then subtract the result of averaging (one complex 
number for each baseline, channel, IF) from the original UV data.
Right now I am at ABQ but having returned back on Tuesday I'll work to do 
it.

:)

Leonia

******************************************************************************
Dr. Leonid Kogan
1221 Apache Dr.
Socorro, NM 87801
(505) 838-1216
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On Thu, 14 Sep 2006, Frazer Owen wrote:

>
>    Dear Eric et al,
>
>    I have been working with GMRT continuum data for the first time.
> I find that there is an artifact in the center of the field which limits
> severely
> the noise. It looks a little like a correlator offset but is a bit messy.
>
>    To explore the effect, I have averaged the residuals from my imaging
> (after UVSUB) over the full 10 hours of the run. I then looked at the
> results with POSSM by baseline and polarization. There are 124 channels.
>
>    The result shows that on some baselines there is a coherent signal which
> appears to be approximately constant. In general it has some spectral shape
> in amplitude. Sometimes,it is a fast sine wave sometimes it only has a
> little
> structure. Usually the phase across the 124 channels changes coherently.
> Sometimes I see a less serious problem of a narrowband birdy as well.
>
>    I would like to try to subtract this averaged signal from each
> visibility
> in the database to see if that will remove the effect or at least reduce it.
> However, there is no way that I can find to do this in AIPS. Thus I
> am requesting an experimental task which allows me to subtract the
> grand average of each baseline and channel from the time original
> uv database used to make that average.
>
>    One can think of many wrinkles on such a task for general use but
> right now I would just like some way to try out making such a correction.
> If this proves useful, then it would be possible to do something fancier.
> Leonia is looking into it but maybe Eric can see some way to do this with
> little or no work.
>
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