C.9 Final Calibration Steps

  1.  If you used AVSPC to reduce the size of the data set used in determining calibration, you must copy your final calibration tables back to the full-size data set. This can be done with task TACOP. For bookkeeping purposes, it may be best to copy over all the CL tables with the same table numbers in both the averaged and un-averaged data sets. Copy the FG table as well, since any data which are bad in the averaged data set will be bad in the full resolution data set. After inspecting the data with UVPLT or VPLOT, run EDITR, TVFLG, CLIP, SPFLG, or other data editor to edit the bad data from the calibrated spectral-line data set.
  2.  After you have corrected the bandpass for spectral line data, you may want to correct for the change in frequency by the motion of the antennas with respect to the Sun etc.. This is done with CVEL, after the source velocities are entered in the SU table with SETJY. For a detailed description see 9.5.5.
  3.  Polarization calibration still remains, if desired, and if all the appropriate calibration sources were observed. This can be done in a variety of ways; see 9.5.7 for details.
  4.  Finally, apply the calibration to the visibility data and make single-source data sets using SPLIT. (Some people might wish to use SPLAT to average over time as well as spectral channel.) Inputs for a continuum observation are SOURCES = ’ ’; BIF = 0; EIF = 0; DOPOL = -1 (or 1 if polarization calibration was attempted); DOBAND = 1; DOUVCOMP = 1; NCHAV = 0; APARM = 2,0; DOCALIB = 1; GAINUSE = highest CL table. For a spectral-line observation, set APARM = 0, because you don’t want to average over frequency. Use OUTDISK and OUTCLASS as appropriate for your computer and record-keeping purposes.

The single-source data sets are now ready for imaging and possible self-calibration. At this point, it is a good idea to look at the amplitude check source ‘CAL-AMP’ using tasks such as UVPLT, WIPER or VPLOT in order to see if there are any antenna gain calibrations that must be adjusted. Doing a WIPER for each target source is a good idea also, because there may be discrepant amplitude points due to interference or poor fringe fits (among other things). The task WIPER makes UVPLT like plots but is designed to do flagging.