Date: Tue, 04 Apr 2006 18:39:47 -0400
From: Ed Fomalont <efomalon@nrao.edu>
Subject: Re: A few uber comments

Hello all,

    One hybrid task we should consider in our thinking is the
equivalent of the AIPS CLCOR and UVFIX.  These are tasks which apply
corrections to the visibility amplitude and phase for antenna position
errors, source position errors, additional extinction corrections,
etc.  UVFIX actually changes the visibility data, CLCOR produces
calibration tables.  The use of CLCOR and UVFIX is more common for
VLBA data than for VLA data.

    How should these correction tasks be implemented and accessed in
casa?  Should they be applied to the data set, ie. 'DATA' to
'CORRECTED_DATA' like UVFIX, or should cal tables be made for each
type?

    A NEW WRINKLE for these methods is that the ms table needs
modification.  For example, if you change the position of a source
(for example, an incorrect source position was used for a calibrator),
how should the table with the source positions be modified?  Updated?
Duplicated with the new position?  What happens if you make a mistake
and want to redo the source position shift and also keep
accountability?


   CLCOR and UVFIX have the following options, separated into my view
of 'general' and 'specialized' ones.  These opcodes have been adhoc
additions over the years, and some of the methods could be combined
and a few outdated.  Clearly each method (eg, OPAC) would see a small
number of input parameters in cass however it is implement.

OPCODE: General
POLR: R-L phase difference
PHAS: RATE: Change phase and rate of an antenna
CLOC, Antenna residual delay
OPAC: Change atmospheric opacity
GAIN: Polynomial form of gain vs elevation
ADEL: ATMO, TROP:  Various atmosphere phase corrections
PANG: Parallactic angle correction (in casa already)
IONS: Apply ionospheric phase for input GPS data
ANTP, ANTC; Correction antenna position and/or source position
UVFIX: Recompute u,v,w, phases accurately for
      epoch change, position change, antenna change, time-offset
      
OPCODE: Specialized
PONT: Gross pointing error for object a field center
PCAL, PCFX: Specialized MKIII VLBI phase cal entries
SBLD, MBDL: Specialized MKIII VLBI delay entries
SSLO: Very VLA specific for non-identical IF pairs
ANAX: Antenna axis-offset term.  Should be part of ANTP.
SUND: Gravitational bending of solar-system objects

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