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| Version 1.9 Build 1488 |
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A Miriad dataset stores correlations for different polarization correlation types (e.g. RR, RL, etc.) in separate records, even if they were observed simultaneously. (Thus, it is up to the Miriad I/O software to properly combine records to form new Stokes correlations.) This is in contrast with AIPS++ which can store polarizations observed at the same time in the same record. Furthermore, BIMA can only observe one polarization per baseline at a time.
mirfiller by default will load visibilities of different polarizations into separate polarization setups; thus, each out MS record will contain a single polarization. This is most appropriate for uncalibrated BIMA data. (Normally, the polarization data are edited and calibrated separately; then, the data is smoothed in time to approximate simultaneous observations.) However, when the data contains multiple, simultaneously-observed polarizations-e.g., VLA data or calibrated and time-averaged BIMA data-it is possible to collect the polarizations into a single polarization setup record using the joinpol option (see setoptions()). Thus, when joinpol is set to True, each MS record will contain the visibilities for all polarizations. One caveat of this option is that data for any polarization not found for a given baseline will be set to zero. Thus, if you use set joinpol=T when loading the raw (unaveraged) BIMA data, it will be N times larger than if it were set to false, where N is the number of different polarizations.