Tuesday, June 19, 2007

Where did R go?

Ok, this is kind of a strange thing. I'm working with Pband data. I've gone through initial flagging, and then I run CALIB. But for some reason it's not finding my R data... so I get 1/2 good solutions and 1/2 failed solutions (because it finds the L just fine). But I look at the data (and when I flagged it too) and it's *there*. Has anyone encountered this? What's going on and how to I fix it? I'm using pretty standard inputs...


amanda said...

Try checking to make sure you haven't accidentally flagged your entire right polarization. Sometimes if you don't have the flag source tag on it will flag everything, not just your source.

Kisha said...

Do you mean the SOURCES adverb within TVFLG or something within CALIB? In TVFLG I'm doing each source individually so set it to something like: SOURCES 'source1','';

I also set "stokes" to 1111 while in TVFLG, which is what I ususally do, so that I can flag LL as well (because for some reason it doesn't pay attention to the adverb STOKES in the inputs).

amanda said...

Even if you set sources='source1', make sure the all source flag on the botton the tvflag screen is not set. Laura had a problem a while ago where her secondary calibrator was accidentally entirely flagged because she had flagged some other source.

Might also be worth copying your flag tables using tacop and then nuking your flag table on the original uvfile and seeing what happens.

The Stokes input paramter sounds good.

Kisha said...

Well, I did discover that the flags were applying to all sources. A quick update using TABED has fixed that so all my flags are applying to the correct sources now.

However, that doesn't fix the fact that it's completely flagging all of the RPOLs. I'm not sure what to do about that. It's fine for my two primary calibrators, but for the secondary ones, CALIB returns:

RPOL, IF= 1 The average gain is 0.000E+00
RPOL, IF= 2 The average gain is 0.000E+00
LPOL, IF= 1 The average gain is 4.445E+00
LPOL, IF= 2 The average gain is 4.590E+00

The gains on the LPOLs look about right. So, I'm wondering about the "PFLAGS" column in the FG table. If it refers to RR, LL, RL and LR, would then a 1111 *marked down* actually mean it was flagging all four? And a 1011 would be flagging RR, RL, LR but not LL?

Unfortunately, if this is the case, I don't know of a good way to fix it - I'm not sure WHY it got recorded that way in the first place, but I have no way of separating out which ones really should have applied to all, which should have been applied to RR and which should be LL, etc. If I knew a way to do that, I could use TABED again and replace values. But I really have no idea...

Kisha said...

Ok an update - LISTR sees all polarizations, when I use the flag table (and it's definitely flagging stuff). So it has to be an issue with CALIB itself.

It turns out that CALIB sometimes has issues with sighal-to-noise especially when the allowable UVRANGE for a given source is very short.

Some things that were suggested for me to try, in decreasing desirableness:

1) specify which antennas which fall in the UVRA (& keep the UVRA in place)

2) work SNR down to 4 or 3 (then on a later calibration, e.g. selfcal, go back to the default of 5)

3) take the minimum # of antennas [aparm(1)] down to 3 and see if that helps (again, later set it back to the default)

amanda said...

Interesting that it would only happen in the R polarizations. Let us know how if you get signal playing with the S/N stuff!

emily said...

i find it really hard to believe that you've lost an entire polarization due to signal to noise. do one quick check: run CALIB with flagver = -1 so that no flagging is being applied and just see if you get any signal in RR.

emily said...

okay, i actually just saw this problem in some gmrt data. i ran calib and it gave this:

gtac4.> CALIB1: Writing SN table 8
gtac4.> CALIB1: RPOL, IF= 1 The average gain over these antennas is 0.000E+00
gtac4.> CALIB1: RPOL, IF= 2 The average gain over these antennas is 1.563E+00
gtac4.> CALIB1: LPOL, IF= 1 The average gain over these antennas is 1.563E+00
gtac4.> CALIB1: LPOL, IF= 2 The average gain over these antennas is 1.528E+00
gtac4.> CALIB1: Found 1080 good solutions
gtac4.> CALIB1: Failed on 1080 solutions

i remembered that these observations had one antenna with a bad bandpass giving lots of bad baselines. i flagged this antenna and then calib found solutions for that polarization. so maybe you still have some (very) bad data somewhere?