[daip] WSRT Tsys correction

[M.A.W. Verheijen]

Dear aips supporter,

thank you very much for your quick reply to my student's inquiry
regarding the Tsys correction for our WSRT data.  There seems to have
been some confusion about what we are trying to achieve, which is
correcting the visibility data from a standard WSRT 21cm spectral line
observation for the time-dependent variations in Tsys.  We started with
a 30min observation of 3C48, followed by 12 hours on our source and
finishing with another 30 min on 3C147.  Every visibility record has its
own Tsys measurement, not only the visibilities of the two calibrators
but also those of the source. 

With good old trusted AIPS we load the UVFITS files into AIPS with FITLD
which creates the TY and GC tables.  Attached is a plot showing the Tsys
behaviour as a function of time for all 14 antennas for LL pol of IF1 as
stored in the TY table. 

Subsequently, we run APCAL that takes the GC and TY tables and produces
a SN table.  This SN table contains the Tsys corrections and shows a
similar behaviour as the points in the attached plot, be it with a
different scale. So far, so good,

Next we try to run CLCAL that takes the CL-1 and SN-1 tables to produce
a new CL-2 table which we can then apply with SPLAT to produce a new
dataset in which the Tsys correction has actually been applied to the
visibility data.  Our problem lies with the behaviour of CLCAL.  Since
all visibility records have their own entry in the SN table,
interpolation in time is not necessary.  Therefore we use
INTERPOL='SELN'.  We want to apply the Tsys corrections not only to the
calibrators but also to the source itself so we select SOURCES='' and
CALSOUR=''.  We also apply a smoothing with SAMPTYPE='MWF' and suitable
BPARM settings.  The full set of parameter settings in included below. 

The problem is that CLCAL does what it is expected to do, but the new
CL-2 table it produces only contains data for the two calibrators.  The
12-hour timerange that contains the visibility data of our source has no
data in the CL-2 table.  Somehow, it seems as if CLCAL ignores any
source that it can not identify as a known calibrator source. 

Any suggestion you may have to fix this problem would be very much
appreciated. Many thanks in advance!

 Best wishes from Groningen,

 Marc


-- 
*************************************************************************
* Marc A.W. Verheijen                                                   *
* Kapteyn Astronomical Institute    Phone : +31-50-363-4077             *
* Postbus 800                       FAX   : +31-50-363-6100             *
* 9700 AV  Groningen                Email : verheyen at astro.rug.nl       *
* The Netherlands                   URL   : www.astro.rug.nl/~verheyen  *
*************************************************************************


AIPS 3: CLCAL     Task to manage SN and CL calibration tables
AIPS 3: Adverbs     Values                 Comments
AIPS 3: ----------------------------------------------------------------
AIPS 3: INNAME     'PPOBS08'               Input UV file name (name)
AIPS 3: INCLASS    'UVDATA'                Input UV file name (class)
AIPS 3: INSEQ         1                    Input UV file name (seq. #)
AIPS 3: INDISK        1                    Input UV file disk unit #
AIPS 3: SOURCES    *all ' '                Source list to calibrate
AIPS 3: SOUCODE    ' '                     Source "Cal codes"
AIPS 3: CALSOUR    *all ' '                Cal sources for calibration
AIPS 3: QUAL         -1                    Source qualifier -1=>all
AIPS 3: CALCODE    ' '                     Calibrator code '    '=>all
AIPS 3: TIMERANG   *all 0                  Time range to calibrate
AIPS 3: SUBARRAY      0                    Subarray, 0=>all,
AIPS 3: ANTENNAS   *all 0                  Antennas selected, 0=> all
AIPS 3: SELBAND      -1                    Bandwidth to select (kHz)
AIPS 3: SELFREQ      -1                    Frequency to select (MHz)
AIPS 3: FREQID       -1                    Freq. ID to select.
AIPS 3: OPCODE     'CALI'                  Operation 'MERG','CALI',
AIPS 3:                                    'CALP'; ' ' => 'CALI'
AIPS 3: INTERPOL   'SELN'                  Interpolation function,
AIPS 3:                                    choices are: '2PT','SIMP',
AIPS 3:                                    'AMBG','CUBE','SELF','POLY',
AIPS 3:                                    'SELN'; see HELP for details
AIPS 3: CUTOFF        0                    Interpolation limit in
AIPS 3:                                    time (min); 0=> no limit.
AIPS 3: SAMPTYPE   'MWF'                   Smoothing function
AIPS 3: BPARM         0.2         0.2      Smoothing parameters
AIPS 3:               0.2         0.2         0.2      *rest 0
AIPS 3: ICUT          0.1                  Cutoff for functional forms
AIPS 3: DOBLANK      -1                    Blanked value interpolation
AIPS 3: DOBTWEEN     -1                    > 0 -> smooth all sources
AIPS 3:                                    together; else separate them
AIPS 3: SMOTYPE    ' '                     Data to smooth
AIPS 3: SNVER         1                    Input SN table, 0=>all.
AIPS 3: INVERS        1                    Upper SN table vers in a
AIPS 3:                                    range.  0=>SNVER
AIPS 3: GAINVER       1                    Input Cal table 0=>high
AIPS 3: GAINUSE       2                    Output CAL table 0=>high+1
AIPS 3: REFANT        8                    Reference antenna 0=>pick.
AIPS 3: BADDISK    *all 0                  Disks to avoid for scratch

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