The ATCA Forum

Hi Mark,

I've been thinking about the uvplt of the two calibrators. Even in the uvplt of the raw visibilities before any flagging/calibration, I still couldn't see any region on the real-imag plane which might become disks/ellipses afterwards. The data just look similar to the uvplt that I've shown, and include more "wild" points. Is it because of any corrupted calibrator data so that I just can't reach that ideal plot, or the distribution of these points will change to a better state after calibration/flagging?

Thanks again!

Tai-An

Hi Tai-An,

I couldn't figure it out until I loaded the data for that day and had a closer look.
I think the main problem is that some of your data suffers from shadowing at the start of the observation.
There were also two scans on 1934 - I flagged the second one around 18:50 since it looked rather bad on the plot.
The following commands take care of this (run this before the uvsplit and calibration steps):
uvflag vis=myvis.uv "select=shadow(25)" flagval=flag
uvflag vis=myvis.uv "select=time(18:41,18:54)" flagval=flag
I'm not sure exactly what happened during the observation, but I see there was a stow command at 16:28 and a new dcal (delay calibration) at 18:52.
There is some bad RFI at 9 GHz from about 23:30-23:45, this has affected the calibrator scan around that time, you may need to flag this time range as well for best results.

In any case flagging the shadowed data and the second 1934 scan seems to have cleared up the real/imag plots.

Cheers,
Mark

Hi Mark,

I've tried to flag the shadowed data and the second 1934 scan as you suggested, but it seems that there are still ~3 "wild" points in 1934's uvplt: And 0023-263 doesn't look good either: While I don't know what's going on, I wonder if I can flag bad points directly on the real-imag plane? Also, it seems that I copied the calibration tables of 1934 to 0023 using gpcopy before calibrating 0023. Is it the correct procedure? (In Miriad's webpage they calibrate 1934 and 0023 separately and then use gpboot after calibrating 0023...)

Thanks again!

Tai-An

Hi Tai-An,

I've emailed you my processing script so you can compare the results

Cheers,

Mark