Currently the receiver position angle is not read from the RPFITS file and a position angle of zero is assumed. This severely hampers correct handling of polarimetry. In the future we aim to define a general framework and populate the RPFITS files with the data required for transparent polarimetric calibration.
It is possible that there is a phase offset between polarisation which will effect the phase of the cross polarisation correlation, and so give rise to spurious polarisation. rotate_xyphase can be used to correct for this error. At this point, the user must know how to determine the size of the phase offset themselves.
ASAP> scans.rotate_xyphase(10.5) # Degrees
Note that if this function is run twice, the sum of the two values is applied because it is done in-situ.
A correction for the receiver parallactic angle may need to be made, either because of how it is mounted or if parallactifiying had to track at 90 degrees rather than 0. Use rotate_linpolphase to correct the position angle. Running this function twice results in the sum of the corrections being applied because it is applied in-situ.
ASAP> scans.rotate_linpolphase(-20) # Degrees; correct for receiver mounting # Receiver was tracking 90 degrees rather than 0 ASAP> scans.rotate_linpolphase(90)