UVPLT shows interesting image!

[Mandy]

Hi

I'm trying to reduce data for the first time and following the instructions carefully. Having split and flagged data I'm now following the calibration instructions. I've got as far as mfcal, gpcopy, gpcal and now I've tried uvplt. For the first file I get the following image:
uvplt vis=1934-638.1419 stokes=i axis=real,imag options=equal,nobase,nofqav device=/xwindow

snapshot1.png (9.28 KiB) Viewed 134404 times

For the following files e.g uvplt vis=1934-638.1664 stokes=i axis=real,imag options=equal,nobase,nofqav device=/xwindow i get this:

snapshot2.png (21.78 KiB) Viewed 134405 times

The second one is what I was expecting to see and from the 7 files 6 of them are indeed like that - it is just the first one that looks odd.

Has anyone else had an image similar to this, should I be worried about it?

Any thoughts are welcome.

Thanks, Mandy

[len067]

Hi Mandy,

Welcome to the ATCA Forum ... that's certainly the coolest uvplt I've seen to date Unfortunately, it doesn't look quite right. Even in your second plot the spread of the points looks to high. I noticed that the frequency of the input visibility file for the first plot is different to your other example - are the 7 files that you're referring to different parts of the band for the same observation? i.e. did you split up the band? It might be worth doing a uvspec to make sure that the bandpass correction looks good for each of the files.

Cheers,

Emil.

[Mandy]

Hi Emil!

Yes - my supervisor nicknamed it Rudolph!! As it is my first attempt I was just doing a quick flag of the data and then following the steps through to see what issues arose so I know the spread is not as good as it could be for the second. Yes the files are all different parts of the band for the same observation; I did uvsplit after atlod and before flagging. I'll try uvspec and see what happens.

No doubt I'll be on here quite a bit!

Cheers

Mandy

[Mandy]

Hi Emil

I tried uvspec following the userguide instructions as below:
uvspec vis=1315-46.1750 select=ant[1] stokes=xx,yy interval=15 options=nocal,nopol,nopass axis=freq,phase yrange=-185,185 device=x/window nxy=5,6

however using the () brackets gave me the error 'Badly placed ()'s' changing them to [] brackets returned 'uvspec: No match' leaving them out gave '### Fatal Error: Unrecognised selection command: ant1'

I'm obviously doing something wrong here but don't know what!

Any idea's

Thanks

Mandy

[Mandy]

I found what I was doing wrong! I forgot the " "

Cheers

Mandy

[Mandy]

Hi Emil

I forgot to mention that the second of the two images in the first post is from a Zoom band.

Having done uvspec for the two files above this is what I got; the first image being for the first image above which isn't right:

snapshot3.png (30.61 KiB) Viewed 134393 times

This is for the second image which is a zoom band;

snapshot4.png (69.28 KiB) Viewed 134393 times

Antenna 4 was out of action that night; I found it difficult to read the text and enlarging it didn't help much

It would seem there are phase errors on the first image; indeed while on target during the night there were tracking errors on ant 2 and 3 of up to 28", advice from DA (we were remote observing) was not to worry unless there was drift on the calibration source - there wasn't.

Could this be part of the problem? If so do I need to flag or indeed ignore the baselines with the big phase differences. We are mainly interested in the zoom band data.

Thanks in advance

Mandy

[len067]

Hi Mandy,

It's good to hear that you worked out the uvspec problem - it was indeed the missing quotes.

For your uvspec plots, did you plot it for 1934-638? I noticed that when you were debugging your uvspec command you included the source 1315-46 ... it's worthwhile sticking with 1934-638 for now because until that source is well calibrated you can't really rely on anything else being right. Also can you remove the "nocal,nopol,nopass" options because that's just going to show you the uncalibrated data. Ideally, what you should see is a flat phase at 0 deg (with a small amount of scatter) and if you plot the amplitude (instead of the phase) it should show the amplitude of the flux calibrator to within about a percent.

Cheers,

Emil.

[Mandy]

Hi Emil

I did as you suggested (I should have used 1934-638 in the first place!) and the plots look exactly as you describe them.This is for the continuum spectrum plotting phase:

snapshot5.png (9.16 KiB) Viewed 134386 times

This is plotting amplitude:

snapshot6.png (9.16 KiB) Viewed 134386 times

This all looks OK to me, so I've still no idea why the uvplt for this looked so odd.

Cheers

Mandy

[len067]

Hi Mandy,

That's looking a bit better ... could you also remove the yrange specifier so that it is automatically scaled? It's a bit hard to see the details in the plot with a +/-185 range.

Cheers,

Emil.

[Mandy]

Ah -yes of course!