The presence of polarimetric measurements in the IMB-FITS file is described in the POLAR column of the BACKEND table. For a non-polarimetric scan, all the chunks in the POLAR column have the NONE value. For a polarimetric scan, values can be NONE, AXIS, REAL or IMAG (note that non-polarimetric chunks -NONE- can be mixed with polarimetric ones).
When processing a polarimetric scan, MRTCAL will offer 2 modes:
Finally, the polarimetric status (does this scan contains polarimetric data?) is saved in the index file. The command MFIND /POLARIMETRY YES|NO|* allows to make the desired selections in this context.