[daip] AIPS. VTESS: mem mapping

[Eric Greisen]

On 8/2/2020 3:20 AM, Alexey Nikonov wrote:
> Thank you for your answer, Eric!
>
> I`ve tried VTESS with different odd inputs, but didn't get the result. 
> Did you have experience on MEM mapping? Maybe other software exists to 
> make MEM a little easier?


You might try giving VTESS the DIFMAP Clean image as the initial guess 
in IN3NAME.  I have little experience with MEM.  Multi-scale Clean in 
IMAGR sometimes helps with extended sources.

Eric Greisen

>
> чт, 30 июл. 2020 г. в 01:05, Eric Greisen <egreisen at nrao.edu 
> <mailto:egreisen at nrao.edu>>:
>
>     On 7/29/2020 2:48 PM, Alexey Nikonov via Daip wrote:
>>     Hello,
>>
>>     I`m writing to ask help in mem VTESS mapping. Can I?
>>
>>     I`ve self-calibrated and restored image of an extended source
>>     1308+326 with CLEAN in DIFMAP. So I know the estimate of noise
>>     level from this map.
>>
>>     Loaded to AIPS calibrated UV-file just to do VTESS mem
>>     deconvolution. Done IMAGR with 0 iterations to obtain beam and
>>     dirty map.
>>     As I know in CLEAN image results I`ve pick the same cellsize as
>>     in DIFMAP and twice image size compared to source area, that can
>>     be seen in CLEAN image.
>>
>>     After that VTESS couldn`t find a solution. Instead of extended
>>     structure I can see only one Gaussian peak and noise.
>>
>>     I couldn`t find many recommendation to VTESS. Documentation says
>>     that noise is crucial parameter, so I played with it, but
>>     nothing changed. Also played with FLUX parameter and number of
>>     iterations.
>>
>>     Can you please help :)
>>
>>     -- 
>>     Sincerely yours,
>>     Aleksei Nikonov
>>     AstroSpace Center,
>>     Lebedev Physical Institute,
>>     Moscow, Russia
>>
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>>     Daip at listmgr.nrao.edu  <mailto:Daip at listmgr.nrao.edu>
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>
>
>     VTESS is a peculiar task whose author was never even in the AIPS
>     group.  It can do nice things but with strange inputs at times. 
>     The Y2K test we run on a Cygnus A data set sets NOISE=.0024 with
>     is close to the noise in the result.  But FLUX is set to -18 (note
>     minus sign!) when the actual flux will turn out to be ~200 Jy.  In
>     other words odd inputs are needed to kick the task into converging
>     on a good answer.  (It did not work when I set FLUX=200 despite
>     the excellent quality of the data.)
>
>     Good luck
>
>     Eric Greisen
>



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