Copying polarisations

As of version 5.6.1, CASA cannot deal with single polarisations on some antennae when generating a Stokes I image. This results in the telescope being flagged and sensitivity thus lost. To remedy this, the copy_ms_pols.py script copies the 'good' polarisation to the non-observed polarisation.

For Stokes I only, this doesn't artificially affect the sensitivity of the observation as the correlated noise between the two polarisation negates the sqrt(2) factor you would get from having both polarisations available. It is not advised to use this script if you are doing polarisation work.

Usage

The script can be used simply as follows (replacing everything in <>):

For self-contained CASA (v5 & 6):

casa -c <path_to_vlbi_pipeline_repo>/copy_ms_pols.py <measurement_set> <input_file>

For modular CASA (v6+):

python <path_to_vlbi_pipeline_repo>/copy_ms_pols.py <measurement_set> <input_file>

You need to provide an input (ascii) file which tells what polarisation should be copied. Each line corresponds to a new command and should have the format as follows:

<antenna>:<pol_from>-><pol_to>

e.g., EF:LL->RR means transfer polarisation LL to polarisation RR on telescope Effelsberg (EF)