Importing data
When importing data, the violetfits_to_uvt script assumes by default
the data is unpolarized and produces the pseudo-polarisation
state "None" from the UVFITS file, by a properly weighted combination
of the two parallel hand states if more than one state is present. The
weighting is based on the relative noise in both polarization states.
Full polarization information can be preserved by adding the magenta /STOKES option to the magenta@ fits_to_uvt command.
The magentaREAD UV command will read data with any polarization state(s).
Processing data
On the contrary, practically all [rgb]1,0,0IMAGER commands cannot handle
more than 1 polarization state. So far, only two commands fully support polarized
data: magentaUV_TIME and magentaSTOKES.
Some imaging strategies cannot be used directly on polarized data.
Also, the automatic definition of supports (magentaMASK /THRESHOLD)
only makes sense on Stokes I or parallel hand polarization states, not
on Stokes Q,U,V or cross-hand states. The same applies to spectral
line identifications.
The script violetself-polar.ima just does that, and follows the naming
conventions used by the magentaMAP_POLAR command. It contains the following commands
The magentaMAP_POLAR command works through data files that follow
conventional naming rules to identify them. The implicit rule is
that Stokes S (where S is any of I,Q,U,V) is stored in a file
of name 'NameBegin'"-N"'NameEnd', e.g. if 'NameBegin' is My_Data
PIPELINE processing
The PIPELINE tools does not automatically handle polarization data.
However, through judicious use of the magentaPIPELINE SELECT
and magentaPIPELINE FIND commands with ad-hoc filters, imaging,
including self-calibration, is possible through custom (though simple)
scripts.
CATALOG ! No catalog, no Line emission
! "Split the X+Y (XX,YY,XY,YX) UVFITS file into I,Q,U,V Stokes UV tables"
@ stokes-split &1
! Setup the pipeline
IMAGER\PIPELINE ?
IMAGER\PIPELINE organize ! " Move UV tables to RAW/"
sic mkdir UVFITS
SIC\SYSTEM " mv *.uvfits UVFITS/"
SIC\SYSTEM " mv RAW/&1.uvt .." ! "Remove the X+Y UV table from RAW/"
!
! Select the I image for self-calibration
let all%filter *-I
IMAGER\PIPELINE select
IMAGER\PIPELINE compute
!
! Apply self-calibration solution to I,Q,U,V data
let all%filter *
IMAGER\PIPELINE find
IMAGER\PIPELINE select
IMAGER\PIPELINE collect
IMAGER\PIPELINE apply
! Image every thing consistently
IMAGER\PIPELINE image
PIPELINE SAVE
Analysing data
The magentaMAP_POLAR command allows to derive images
of the Polarized intensity and/or fraction and Polarization angle,
as well as display of the polarization vectors onto a background image.
So far, the command only works for a single plane image.
My_Data-I+C.uvt, My_Data-U+C.lmv-clean, etc..
Next: The STOKES command
Up: Polarization Handling
Previous: Polarization Handling
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Gildas manager
2023-06-01