[daip] [!5455]: aips - CALIB task for amplitude self-calibration : How the details are implemented ?

[Eric Greisen]

Eric Greisen updated #5455
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       Staff (Owner): Eric Greisen (was: -- Unassigned --)
              Status: Closed (was: Open)
                 Due: - Cleared - (was: 09 September 2014 06:57 AM)

CALIB task for amplitude self-calibration : How the details are implemented ?
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           Ticket ID: 5455
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/5455
           Full Name: Jae-Young Kim
               Email: jykim at astro.snu.ac.kr
             Creator: User
          Department: AIPS Data Processing
       Staff (Owner): Eric Greisen
                Type: Issue
              Status: Closed
            Priority: Default
      Template Group: Default
             Created: 05 September 2014 06:57 AM
             Updated: 05 September 2014 03:02 PM



We found that self-cal was not reliable with fewer than about
7 antennas in fact.  CALIB will simply try to fit the data to the
model.  Since one antenna phase is defined to be zero, there 
is a slight redundancy from the 3 measured phases.  But your
original calibration and image are crucial even for phase and
they totally determine the amplitude gains.  (Take your CC file
and multiply each component by two and all gains will change
by sqrt(2).)  For polarization, things are even worse.  You have
6 phases but require 5 numbers (phase for antennas 2 and 3
in R and phase for all 3 antennas in L since you require the
R-L phase for polarization calibration).  I suspect that the
science you are trying to do will not be reliable except perhaps
for very strong sources.

And frankly I do not understand this need to use difmap.
AIPS' IMAGR is a very powerful imaging task.

Eric Greisen






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