READme File for Argus Beam-2/3 swap Issue

All Argus data collected before 2018.10.22 19:30 UT have a cable swap
issue between Beams 2 and 3.  This cable mis-match was in the
equipment room such that the Argus Beam-2 channel was connected to
VEGAS channel labled as beam-3, while the Argus Beam-3 channel was
connected to the VEGAS channel labled as beam-2.  Nothing is wrong
with the data, but the positional information for the data labeled as
Beam2 and Beam3 would need to be swapped to be consistent with the
actual positions on the sky for these beams.

The Argus beam naming convention is from 1-16.  Note the GBTIDL naming
convention for "fdnum" is from 0-15, but the actual feed/beam labels
are from 1-16 (as given by !g.s[0].feed within GBTIDL).

---------------------
Listing_argus_beam23:

This file lists all of the affected Argus observing sessions.  If you
find an error with this list, please contact David Frayer.
Eventually, the NRAO/GBO archive will be populated with a warning
message to inform potential archival scientists.


================
Fixing the Issue


There are many different approaches to fixing this issue depending on
the current state of your data.  Originally, IDL example solutions
were derived to assist users (see argus_23swap.pro and
argus_23swapRawSDFITS.pro), but the output files made by these scripts
caused issues with the gbtgridder.  Python solutions were then made,
and these python based solutions work well with the gbtgridder (which
is also in python).  This directory includes these scripts which are
recommended for fixing your data.

-------------------
swap23RawSDFITS.py:

This script can be used to fix the raw SDFITS files.

#Usage: %swap23RawSDFITS.py raw.vegas.C.fits  raw.vegas.D.fits
#Warning: Replaces data in original input files  
#Beam-3 data are in VEGAS Bank-C and Beam-2 are in VEGAS Bank-D 

The script can be used in calibrated SDFITS files where the beam-3
data are in first input name and the beam-2 data are in the second
input name, as long as the data in both files are in the same scan and
integration order.

The file "NOTES_testing" shows how this script was tested and can be
used to understand what is being done.

-----------
swap23.py:

This script can be used to fix calibrated SDFITS files (e.g., KEEP
files) where the input file contains both the beam-2 and beam-3 data
and the data are in the same scan and integration order for both
beams.


#Usage: %swap23.py SDFITSfile.fits
#Warning: Replaces data in original input file 


============

If you have questions or find issues with the scripts and/or your
data, please contact David Frayer.