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Simple Reduction - II

The example below has been supplied by Alberto, though some administrative details have been left out to make the example less cluttered.

First we define some convenient variables, so we can re-use them in the script. The rule of thumb should be any number, or certainly multiply occuring text, should be used in a (shell) variable. That rules is not quite followed in the current example:

  set FILE="c0001.n604_coC.1.miriad"
  set SRC="NGC604"
  set CAL1="0205+322"
  set CAL2="0237+288"
  set PBCAL="3C454.3"
  set NOISE="NOISE"
  set FLUX="URANUS"

  set WIDE="channel,1,1,15,1"
  set LINE="velocity,63,-317.521,2.54,2.54"
  set CAL=$CAL2
  set OCAL=$CAL1
  set RESTFREQ="115.271202"
  set REFA=9

Some of variables may be quite obvious, others less. For example, the setting for LINE= less came from gleaning the output of uvlist:

  % uvlist vis=$FILE options=spectra
 rest frequency     : 115.27120 115.27120 115.27120 115.27120 115.27120 115.27120
 starting channel   :         1        16        79       142       157       220
 number of channels :        15        63        63        15        63        63
 starting frequency : 111.47148 111.08239 111.05307 114.93370 115.32280 115.35211
 frequency interval :  -0.03125  -0.00049  -0.00049   0.03125   0.00049   0.00049
 starting velocity  :  9854.752 10866.791 10943.046   849.513  -162.527  -238.782
 ending velocity    : 10992.691 10945.532 11021.788  -288.426  -241.268  -317.523
 velocity interval  :    81.274     1.270     1.270   -81.274    -1.270    -1.270

First we note that the data set from CARMA is a single miriad dataset that contains all the sources. It is often , except in the most simple cases, much more convenient to keep track of things if the data is copied to single-source (or even single-setting) datasets:

  foreach i ($SRC $CAL1 $CAL2 $PBCAL $NOISE $FLUX)
    uvcat vis=$FILE out=$i select="-auto,source("$i")"
  end

It cannot be stressed enough to inspect the data data visually , in as many ways as you can imagine. Here are just a few examples:

# phase vs. time
  uvplt vis=$CAL device=/xs line=$WIDE axis=time,phase

# amplitude vs. time
  uvplt vis=$CAL device=/xs line=$WIDE axis=time,amp

# even for the source: it probably be random, unless there are false fringes
# or it is a very strong source
  uvplt vis=$SRC device=/xs line=$WIDE axis=time,phase

  uvspec  ...

As a result of this inspection perhaps we found some suspicious data, and it needs to be flagged. This could be in certain channels and/or time slots. Here is an example to flag a certain time-range for antenna 5:

  uvflag vis=$CAL,$PBCAL,$SRC flagval=flag select="ant(5),time(21:30:00,22:15:00)"

First we proceed with (astronomical) passband calibration, to make sure the trends we saw in phase vs. time are not washed out by passband slopes. Notice we're compressing the whole time-ranges to get a single passband shape for all times:

  
  mfcal vis=$PBCAL line="channel,282,1,1,1" interval=999 refant=$REFA

and inspect the result

  
  uvspec vis=$PBCAL axis=chan,phase line="channel,282,1,1,1" device=/xs interval=999 yrange=-180,180

copy the passband from the PBCAL to the CAL

  
  gpcopy vis=$PBCAL out=$CAL options=nocal

Create new dataset with calibration applied, otherwise linetype averaging does not work properly. Use all wideband channels.

  uvcat vis=$CAL out=$CAL.pb select="window(1,4)"

Proceed with amplitude-phase calibration

  gpcopy vis=$PBCAL out=$FLUX options=nocal
  uvcat vis=$FLUX out=$FLUX.pb select="window(1,4)"

  selfcal vis=$FLUX.pb options=apriori,amp,noscale interval=0.1 line="channel,1,1,30,1" refant=$REFA
  bootflux vis=$FLUX.pb,$CAL.pb primary=$FLUX line="channel,1,1,30,1" taver=999

Self calibrate the phase calibrator, with passband calibration applied, and imposing the flux found by bootflux solution

  selfcal vis=$CAL.pb line="channel,1,1,30,1" options=amp,noscale,apriori flux=1.2 interval=20 refant=$REFA

Inspect again. Now each channel should have a zero phase

  uvspec vis=$CAL.pb axis=chan,phase line="channel,272,1,10,1" device=/xs interval=999 yrange=-180,180

Show time series of selfcalibrated wideband channels:

  uvplt vis=$CAL.pb axis=time,phase device=/xs line="channel,1,16,15,1"
  uvplt vis=$CAL.pb axis=time,amp device=/xs line="channel,1,16,15,1"

Or for a phase-only calibration, we self calibrate on the phase calibrator, with passband calibration applied. Most of the time the online amplitude calibration seems very good... Note that we are averaging over all wideband channels. Channel linetype averaging does not weigh by bandwidths and/or Tsys. This is why we split out only the continuum windows.

 
  selfcal vis=$CAL.pb line="channel,1,1,30,1" interval=20 refant=$REFA

Inspect the results, again every channel should have zero phase:

  uvspec vis=$CAL.pb axis=chan,phase line="channel,272,1,10,1" device=/xs interval=999 yrange=-180,180

Now show a time series of self calibrated wideband channels:

  uvplt vis=$CAL.pb axis=time,phase device=$device line="channel,1,16,15,1"

Now that all calibration is done, it is a good idea to do some sanity checks. Looking at the gain amplitudes $>1$ indicate that the phase calibrator was weaker than expected, perhaps due to pointing errors,

  gpplt vis=$CAL.pb device=$device yaxis=amp

The phase gains should be smooth now:

  gpplt vis=$CAL.pb device=$device yaxis=phase

Looking at the phase vs time after selfcal, they should be centered around zero:

  uvplt vis=$CAL.pb device=$device axis=time,phase line=$WIDE

The phase vs baseline length plot should be inspected to assess atmospheric decorrelation, it should be flaring at the longer baselines but not overall decline:

  uvplt vis=$CAL.pb device=$device line=$WIDE axis=uvdist,phase options=nobase

And finally amplitude vs. time: it should be about was it was set to in the selfcal if an amplitude selfcal was done:

  uvplt vis=$CAL.pb device=$device line=$WIDE axis=time,amp

In the actual example script it now continues mapping the calibrator, and finally a number of the same set of observations for the source. It can be found in the examples directory as example-blabla.csh.


next up previous contents index
Next: Hybrid Mode Calibration - Up: Simple Reduction Previous: Simple Reduction - I
Peter
2009-10-05