next up previous
Next: Special Calibration Tools and Up: Normal Calibration Procedure Previous: ANTENNA GAINS

APPLY BANDPASS AND ANTENNA GAINS

So far, we have not corrected the visibility data. The flags, bandpass and antenna gain solutions which are stored in the numerous tables (flags, bandpass, and gains) under the uv file directory. If one is happy with these solutions, they can be applied to the visibility data using uvaver by the setup below:

uvaver% inp
Task:   uvaver
  vis      = gc_rx1.lsb.tsys
  select   = source(sgra*, sgrb*, nrao530)
  out      = gc_rx1.lsb.tsys.cal

The data gc_rx1.lsb.tsys.cal is the calibrated data. With uvaver, one can average the data from each chunk to produce a `ch0' data set. The corresponding setup is given below:

uvaver% inp
Task:   uvaver
  vis      = gc_rx1.lsb.tsys.cal
  line     = channel, 24,2,13,16
  out      = gc_rx1.lsb.tsys.cal.ch0

To make a continuum data, the setup below is suggested:

uvaver% inp
Task:   uvaver
  vis      = gc_rx1.lsb.tsys.cal.ch0
  line     = channel, 1,1,24
  out      = gc_rx1.lsb.tsys.cal.cont

If the source has sufficient S/N for selfcal, it would be better to stay with the chunk-based `ch-0' data set. Then, the option of MFS in the self-calibration and imaging process will minimize the residual errors before averaging.

One can break the multi-source file into single source files using uvsplit

uvsplit% inp
  Task:   uvsplit
  vis      = gc_rx1.lsb.tsys.cal
  options  = nowindow

As we have shown, the unwrapped phase across the broad SMA band (2 GHz) shows a large drift for some antennas (particularly for the antennas with long baselines). Even for continuum imaging, the bandpass calibration will be crucial for removing the phase ripples to increase the dynamic range. The calibration feature for multiple frequency windows (or chunks) in Miriad tasks mfcal or smamfcal is highlighted for synthesizing a continuum image from a large number of spectral windows's data.


next up previous
Next: Special Calibration Tools and Up: Normal Calibration Procedure Previous: ANTENNA GAINS
Jun-Hui Zhao (miriad for SMA)
2012-07-09