= CABB Reduction Example =

Data was taken by J Stevens (JBS) and M Voronkov (MV) on the night of 2009-04-01. This experiment is described [http://svn.atnf.csiro.au/trac/operations/wiki/NFO/Development/CABB/Logs/001,here].

This data is a set of 3-point mosaics on calibrators around 0823-500 and 1934-638. This reduction
is to test:
 * bandpass stability on calibrators
 * mosaic reduction with CABB data
 * can we detect polarisation on 1514-241?
 * check for decorrelation at offset pointings

== Loading the data ==

For this example I will load only the data from 2009-04-01_1407 onwards as the RA half-power
point problem was resolved and the observations include a possibly polarised source 1514-241.

The files we are using are:
{{{
4.5G  2009-04-01_1407.C999
4.7G  2009-04-01_1543.C999
2.8G  2009-04-01_1723.C999
1.9G  2009-04-01_1822.C999
3.1G  2009-04-01_1938.C999
}}}
for a total of 17G.

First atlod:
{{{
atlod% inp
  Task:   atlod
  in       = *.C999
  out      = firstnight_1934.uv
  ifsel    =  
  restfreq =  
  options  = noif
  nfiles   =  
  nscans   =  
}}}

We use options=noif since there are actually 4 IFs in each CABB file: IFs 1 & 2 are the 2 GHz 2048 channel
wide-bands, while IFs 3 and 4 are the 4096 channel areas that the zoom bands will use. Since the IFs have
different numbers of channels, ATLOD will fail if you ask it to map the IFs to the same channel axis. After
using options=noif you may select the different IFs using the select=window options.

Let's look at the data using uvplt (this takes quite a while with all the data!):
{{{
uvplt% inp
  Task:   uvplt
  vis      = firstnight_1934.uv/
  line     =  
  select   = -auto,window(1),pol(xx,yy)
  stokes   =  
  axis     = time,amp
  xrange   =  
  yrange   =  
  average  =  
  hann     =  
  inc      =  
  options  = nobase
  subtitle =  
  device   = firstnight_firstlook.png/png
  nxy      =  
  size     =  
  log      =  
  comment  =  
}}}

[[Image(firstnight_firstlook.png)]]

This image shows us that something weird happened - we didn't observe on April 2! A quick
uvindex shows the problem:
{{{
uvindex% inp
  Task:   uvindex
  vis      = firstnight_1934.uv/
  interval =  
  log      =  
  options  =  
}}}
{{{
09APR01:16:58:33.2 aa1              n  6      2049        0      1  318505
09APR01:16:59:34.0 aa2              n  6      2049        0      1  321097
09APR01:17:00:34.0 aa3              n  6      2049        0      1  323689
09APR02:17:01:27.4 aa3              n  6      2049        0      1  326009
09APR02:17:02:03.2 bb1              n  6      2049        0      1  326225
09APR02:17:03:04.0 bb2              n  6      2049        0      1  328817
09APR02:17:04:04.0 bb3              n  6      2049        0      1  331409
09APR01:17:05:38.2 cc1              n  6      2049        0      1  334001
09APR01:17:06:39.0 cc2              n  6      2049        0      1  336593
09APR01:17:07:39.0 cc3              n  6      2049        0      1  339185
}}}

A little quirk has meant that the timestamp is wrong for a few scans. Since the quirk may have
also corrupted the data, we take no chances and flag it out with uvflag:
{{{
uvflag% inp
  Task:   uvflag
  vis      = firstnight_1934.uv/
  select   = time(09APR02:00:00:00)
  line     =  
  edge     =  
  flagval  = flag
  options  =  
  log      =  
}}}

And looking at the data again shows us the following plot.

[[Image(firstnight_aftertimeflag.png)]]

So we can see that we are observing different sources and that the data looks as one would
expect it to. Now let's just look at 1934-638, as we will use it as our primary calibrator.
{{{
uvplt% inp
  Task:   uvplt
  vis      = firstnight_1934.uv/
  line     =  
  select   = -auto,window(1),pol(xx,yy),source(aa1)
  stokes   =  
  axis     = time,amp
  xrange   =  
  yrange   =  
  average  =  
  hann     =  
  inc      =  
  options  = nobase
  subtitle =  
  device   = 1/xs
  nxy      =  
  size     =  
  log      =  
  comment  =  
}}}
Here we use the source name aa1 for the mosaic pointing on 1934-638 with no offset.

[[Image(firstnight_1934_beforecal.png)]]

And we can plot phase too:

[[Image(firstnight_1934p_beforecal.png)]]

And the bandpass:
{{{
uvspec% inp
  Task:   uvspec
  vis      = firstnight_1934.uv/
  select   = -auto,window(1),pol(xx,yy),source(aa1)
  line     =  
  stokes   =  
  interval = 10
  hann     =  
  offset   =  
  options  = nobase,avall
  axis     = freq,amp
  yrange   =  
  device   = firstnight_1934b_beforecal.png/png
  nxy      = 3,4
  log      =  
}}}

[[Image(firstnight_1934b_beforecal.png)]]

Now we calibrate:
{{{
mfcal% inp
  Task:   mfcal
  vis      = firstnight_1934.uv/
  line     =  
  stokes   =  
  edge     =  
  select   = window(1),source(aa1)
  flux     =  
  refant   =  
  minants  =  
  interval = 0.1
  options  =  
  tol      =  
}}}