Invert rejecting all visibilities

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Invert rejecting all visibilities

Postby ncy » Wed Jul 05, 2017 4:20 pm

Hi,

I have a snapshot observation made with H214 array configuration at cm wavelengths. After usual flagging and calibration, I tried form an mfs continuum image with only ant 6, all visibilities were rejected by invert. uvfstats indicates that only ~20% of data were flagged and uvplt also looks fine. I tried using slop with invert, as suggested by another post in the forum, but failed to work.

Best,
Stephen
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Re: Invert rejecting all visibilities

Postby ste616 » Wed Jul 05, 2017 4:30 pm

Hi Stephen,

Can you please post your inputs to invert in full please, and the terminal output?
cheers
Jamie Stevens
ATCA Senior System Scientist
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Re: Invert rejecting all visibilities

Postby ncy » Wed Jul 05, 2017 5:58 pm

sure.

invert vis=test.uv map=test.imap cell=10 imsize=1025 stokes=i robust=2 select="ant(6)" options=mfs

invert: Revision 1.22, 2016/01/20 03:03:49 UTC

Reading the visibility data ...
Making MFS images
Visibilities accepted: 0
### Warning: Visibilities rejected: 922050
### Fatal Error: No visibilities to map
ncy
 
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Re: Invert rejecting all visibilities

Postby ste616 » Wed Jul 05, 2017 7:01 pm

Thanks Stephen. Based on the output, I would first check that antenna 6 is present in the data, because I can't immediately see any problem with the command.
cheers
Jamie Stevens
ATCA Senior System Scientist
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Re: Invert rejecting all visibilities

Postby ncy » Wed Jul 05, 2017 8:55 pm

I saw the data points when plotting out with uvplt

uvplt vis=test.uv device=/xs select="ant(6)" stokes=i options=nobase

so those are not flagged, but for some reason just rejected by invert. I can send around the data for a closer look if needed.
ncy
 
Posts: 7
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Re: Invert rejecting all visibilities

Postby ste616 » Wed Jul 05, 2017 9:17 pm

Yes, I think we may need to look at the data. What does the output of that uvplt command look like in PGPLOT?
cheers
Jamie Stevens
ATCA Senior System Scientist
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Posts: 206
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Re: Invert rejecting all visibilities

Postby ncy » Thu Jul 06, 2017 1:29 pm

Hi Jamie,

I've attached a few plots, made with the following commands respectively

uvplt vis=test.uv stokes=i select="ant(6)" nxy=3,2 device=plt1.png/png
uvplt vis=test.uv stokes=i select="ant(6)" nxy=3,2 axis=freq,amp options=nofqav device=plt2.png/png
uvplt vis=test.uv stokes=i select="ant(6)" nxy=3,2 axis=uc,vc options=nofqav device=plt3.png/png

Best,
Stephen
Attachments
plt1.png
plt1.png (9.57 KiB) Viewed 2119 times
plt2.png
plt2.png (16.55 KiB) Viewed 2119 times
plt3.png
plt3.png (7.65 KiB) Viewed 2119 times
ncy
 
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Re: Invert rejecting all visibilities

Postby Mark.Wieringa » Thu Jul 13, 2017 10:13 am

Hi Stephen,

Have you tried a smaller cellsize? Try 1 or 2 and see what happens. It may be that the long baselines are falling of the edge of the uv grid.
On another note, from your uv plot it doesn't look like you have enough data for a 2-d image. Unless test.uv is just a small subset of the data.

Cheers,

Mark
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Re: Invert rejecting all visibilities

Postby ncy » Thu Jul 13, 2017 1:12 pm

Using a small cellsize as suggested works perfectly! Thanks Mark. The observation was a snapshot with very short integration time of a few min only.
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