[daip] questions regarding prtan and imagr
Hiroko Shinnaga
shinnaga at caltech.edu
Tue Jun 3 06:07:54 EDT 2008
Dear Eric,
Thank you very much for your kind response to my questions.
All the tools that you mentioned are useful.
Conclusion is that somehow the problem was gone now.
I calibrate the data a bit differently and that might have helped
fixing the problem. Everything looks working properly.
> Try the task PRTAB on your INEXT='AN' file. My bet is that you
> have only 8 rows in that table. The AN file is not used a great
> deal - it provides labels for antennas in plotting tasks but that
> is not essential and the tasks should run without them. The only
> task that requires the AN table in a completely essential way is
> UVFIX. You cannot run that task without an AN table that is correct.
You are right. I found only 8 antennas there. It's good to know
that the antenna table matters only when we do "uvfix".
> The weights are with the data - displayed by PRTUV etc. Check them
> that way. The weighting in IMAGR is wuite complex - it does the
> weight summing and normalizing starting with the weights in the
> data samples themselves. Note that those weights are assumed to be
> proportional to 1/uncertainty squared.
I tried "PRTUV" and confirmed that all weightings look reasonable now.
Result images look reasonable and very nice.
It's good to know that I can use PRTUV if this kind of weird things
happen.
Thanks very much again. I appreciate your great help.
Hiroko
On 2008/05/19, at 7:47, Eric Greisen wrote:
> Hiroko Shinnaga wrote:
>>
>> It's good to know that UVPLT does not use the antenna table. If I
>> do PRTAN,
>> the output for the 8 antennas looks reasonable, like
>> .............................................
>> Array reference position in meters (Earth centered)
>> Array BX= -5462428.40757 BY= -2491960.45618 BZ=
>> 2286526.65343
>> Polar X = 0.00000 Polar Y = 0.00000 arcsec
>> Earth rotation rate = 360.9856449756 degrees / IAT day
>> GST at UT=0 = 202.5367277361 degrees
>> UT1-UTC= 0.0000000 Data time(UTC )-UTC= 0.0000000
>> seconds
>> Solutions not yet determined for a particular FREQID
>> Mount=ALAZ Axis offset= 0.0000 meters IFA IFB
>> Feed polarization type = R L
>> Ant 1 = AN01 BX= 0.0000 BY= 0.0000 BZ=
>> 0.0000
>> Ant 2 = AN02 BX= 90.4130 BY= -276.1790 BZ=
>> -263.6168
>> Ant 3 = AN03 BX= 85.4508 BY= 1.9548 BZ=
>> -209.1038
>> Ant 4 = AN04 BX= 37.0243 BY= -405.5341 BZ=
>> -149.5777
>> Ant 5 = AN05 BX= 154.5661 BY= -60.0895 BZ=
>> -399.4778
>> Ant 6 = AN06 BX= 128.0491 BY= 73.5067 BZ=
>> -295.3008
>> Ant 7 = AN07 BX= 139.7886 BY= 19.8421 BZ=
>> -336.0244
>> Ant 8 = AN08 BX= -3.2893 BY= -178.0796 BZ=
>> 14.1085
>> .............................................
>> So, I guess the antenna table is fine except for the fact that the
>> other two
>> antenna's information is not included. Do you agree on that?
> It looks okay - try PRTAB to see if PRTAN is interpreting things
> oddly and omitting some display.
>
>> If the antenna table is used only for the calibration process,
>> would we
>> expect that the final map after processing IMAGR should be correct
>> as long
>> as we process the calibration elsewhere?
>
> Actually the AN table is not even used in calibration so you should
> be able to
> do CALIB (self-cal) when you get the imaging to work.
>
>
>> I understand IMAGR does not use the antenna table now. From where
>> does AIPS
>> get information required for UVWTFN?
>
> The weights are with the data - displayed by PRTUV etc. Check them
> that way. The weighting in IMAGR is wuite complex - it does the
> weight summing and normalizing starting with the weights in the
> data samples themselves. Note that those weights are assumed to be
> proportional to 1/uncertainty squared.
>
> Eric Greisen
>
On 2008/05/19, at 7:33, Eric Greisen wrote:
> Hiroko Shinnaga wrote:
>> Dear AIPS experts,
>> I'm Hiroko Shinnaga, a staff scientist at the Caltech
>> Submillimeter
>> Observatory. I have two general questions regarding tasks of PRTAN
>> and IMAGR.
>> Q1. I'm dealing with some interferometric data that contains
>> 10 antennas in total. I first create FITS file using a
>> calibration tool
>> called MIR (IDL base) and generated a FITS file. Then I read the
>> FITS file to AIPS. When I inspect the data using the task "UVPLT"
>> for example, it looks like it contains all data of all
>> baselines. However,
>> when I use the "PRTAN", I see only information of 8 antennas. From
>> the output of "PRTAN", it seems the antenna table seemed to not be
>> transfered properly. Could you let me know what kind of effect I
>> should expect if I don't have a correct antenna table?
>> Q2. When I tried to process the above image with IMAGR, I found
>> I was able to make sensible image only when I use UVWTFN = ' '
>> (uniform weighting). Does this indicate that something may be
>> wrong for the table that contains weighting information of each
>> antenna?
>
> Try the task PRTAB on your INEXT='AN' file. My bet is that you
> have only 8 rows in that table. The AN file is not used a great
> deal - it provides labels for antennas in plotting tasks but that
> is not essential and the tasks should run without them. The only
> task that requires the AN table in a completely essential way is
> UVFIX. You cannot run that task without an AN table that is correct.
>
> I find your statement in Q2 hard to believe. The weights are part
> of the visibility data (as real, imaginary, weight). You can look
> at them with PRTUV, UVPRT, and even plot them with UVPLT et al. If
> you attempt UVWTFN = 'NA' then you get the actual values present in
> the data. If there is something really wrong with them, then the
> resulting image would be strange. Really wrong means something
> like 10000 for one baseline and 0.001 for the others. Weights that
> are <= 0.0 flag the associated data and so would not appear in any
> image independent of UVWTFN.
>
> Eric Greisen
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