Reference Gain Calibration
Reference complex gain calibration refers to determining the "system" amplitude and phase with high precision as a function of IF band (i.e. integrated over each 500 MHz IF band). A typical reference calibration would cover 34 bands, 2 polarizations, and 13 antennas. I have a routine to retrieve and analyze the data, named refcal_anal.py. Start from a time range during which reference calibration observation occurred
import refcal_anal as ra from util import Time trange=Time(['2017-04-08T05:00','2017-04-08T15:30'])
Ideally, we would like all reference calibrations to have a designated PROJECTID "REFCAL". For all data before May 2017, however, all reference calibrations had PROJECTID of "PHASECAL", but most of them were on 3C273 (1229+020). So I am using:
out=ra.rd_refcal(trange, projid='PHASECAL', srcid='1229+020')
Take a look at the phases (averaged over each band). To change the bands to display, update the "bandplt" parameter (default is [4, 8, 12, 16]). Default is to plot polarization XX (pol=0). To display YY, change to pol=1.
f,ax=ra.graph(out, bandplt=[4,8,12,16], pol=0)
From the plot one can determine which time range has clean enough phases (stable over time), which will be used for averaging to get the reference phase/amp. One can also supply a list of scan indices to indicate scans you want with "scanidx" (default is to use all scans found).
vis=ra.refcal_anal(out,timerange=Time(['2017-04-08T05:00','2017-04-08T07:00']),scanidx=[1, 3, 5, 7, 9, 11, 13])