Cube imaging- No visibility to map

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Cube imaging- No visibility to map

Postby saracmbr » Fri Mar 01, 2013 12:29 pm

Hi,

I've been trying to make a cube image of different stokes parameters but I face the error No Visibility to map.
There is no problem with options=mfs. There is no RFI or phase error in the image field(MFS).
The observation is at 16cm. I just tried a pre-CABB dataset (1.4GHz) and I get the same error.
Can anybody help me to find the problem.

Cheers,
Sara
saracmbr
 
Posts: 38
Joined: Fri Jan 20, 2012 3:40 pm

Re: Cube imaging- No visibility to map

Postby Mark.Wieringa » Fri Mar 01, 2013 1:04 pm

Hi Sara,

it looks like there is some selection happening which results in there being no visibilities left.
E.g., you could be asking to image polarizations that are not present in the data, or the line parameter could be selecting flagged channels only.

Try a prthd in=visfile to see what is present in your visibility file. You can post the results here together with your invert inputs if you are still scratching your head after that..

Cheers,

Mark
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Re: Cube imaging- No visibility to map

Postby ste616 » Sun Mar 03, 2013 11:48 am

Hi Sara,

The most common cause of this problem is due to the incorrect setting of the 'slop' parameter in invert.

By default, invert requires that every spectral channel (in the range that you are trying to image) be good before it will use that visibility. This is almost never the case, and certainly not in the 16cm band.

To allow invert to use visibilities that have flagged channels, set the 'slop' parameter in invert to 0.5 (or higher if you think there are more than 50% bad channels in your selection).
cheers
Jamie Stevens
ATCA Senior System Scientist
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Re: Cube imaging- No visibility to map

Postby saracmbr » Mon Mar 04, 2013 11:07 am

Hi Jamie,

I used slop=1 and it worked. It is 30% of the data flagged. Is this a problem I use slop=1 instead of 0.5?

Many thanks,
Sara
saracmbr
 
Posts: 38
Joined: Fri Jan 20, 2012 3:40 pm

Re: Cube imaging- No visibility to map

Postby ste616 » Mon Mar 04, 2013 11:18 am

Hi Sara,

I wouldn't use slop=1 myself, since this would make invert "use" visibilities that are entirely flagged as bad. In itself, this shouldn't make your image worse, but it could potentially slow down the imaging process.
cheers
Jamie Stevens
ATCA Senior System Scientist
ste616
Site Admin
 
Posts: 211
Joined: Thu Feb 04, 2010 3:27 pm
Location: Paul Wild Observatory Narrabri NSW


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