Bandpass

The baseline bandpasses can be measured after calibration by averaging the complex visibilities over time. We reduce them to station-based values with full complex fits.

Note that there is a degeneracy between some calibration parameters and the bandpass. Because the calibration is performed after applying a guess for the bandpass, phases, delays and curvatures can end up partly in the calibration parameters and partly in the bandpass.

There is an additional complication: We do everything per baseline. The complete solution should 'close' perfectly, which means it can be reduced to station-based parameters. But this may not be true for calibration and bandbass individually. For this reason we apply the remaining (time-averaged) closure errors from the calibration parameters to the baseline bandpasses before reducing them to station-based bandpasses.

Symbolically, we can write (neglecting complex conjugation):

(true signal) = (baseline-cal) * (baseline-bandpass)
              = (station-cal1 * station-cal2) * (station-bandpass1 * station-bandpass2)
              
                                          (baseline-bandpass) * (baseline-cal)        
(station-bandpass1 * station-bandpass2) = ------------------------------------
                                             (station-cal1 * station-cal2)