4 Synthesis Calibration

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Chapter 4
Synthesis Calibration

Inside the Toolkit:

The workhorse for synthesis calibration is the cb tool.

This chapter explains how to calibrate interferometer data within the CASA task system. Calibration is the process of determining the complex correction factors that must be applied to each visibility in order to make them as close as possible to what an idealized interferometer would measure, such that when the data is imaged an accurate picture of the sky is obtained. This is not an arbitrary process, and there is a philosophy behind the CASA calibration methodology (see § 4.2.1 for more on this). For the most part, calibration in CASA using the tasks is not too different than calibration in other packages such as AIPS or Miriad, so the user should not be alarmed by cosmetic differences such as task and parameter names!

4.1 Calibration Tasks
4.2 The Calibration Process — Outline and Philosophy
  4.2.1 The Philosophy of Calibration in CASA
  4.2.2 Keeping Track of Calibration Tables
  4.2.3 The Calibration of VLA data in CASA
  4.2.4 Loading JVLA data in CASA
4.3 Preparing for Calibration
  4.3.1 System Temperature Correction
  4.3.2 Antenna Gain-Elevation Curve Calibration
  4.3.3 Atmospheric Optical Depth Correction
  4.3.4 Setting the Flux Density Scale using (setjy)
  4.3.5 Correction for delay and antenna position offsets using gencal
  4.3.6 Applying JVLA switched power or ALMA Tsys using gencal
  4.3.7 Generate a gain table based on Water Vapor Radiometer data wvrgcal
  4.3.8 Other a priori Calibrations and Corrections
4.4 Solving for Calibration — Bandpass, Gain, Polarization
  4.4.1 Common Calibration Solver Parameters
  4.4.2 Spectral Bandpass Calibration (bandpass)
  4.4.3 Complex Gain Calibration (gaincal)
  4.4.4 Establishing the Flux Density Scale (fluxscale)
  4.4.5 Instrumental Polarization Calibration (D,X)
  4.4.6 Baseline-based Calibration (blcal)
4.5 Plotting and Manipulating Calibration Tables
  4.5.1 Plotting Calibration Solutions (plotcal)
  4.5.2 Listing calibration solutions with (listcal)
  4.5.3 Calibration table statistics (calstat)
  4.5.4 Calibration Smoothing (smoothcal)
  4.5.5 Calibration Interpolation and Accumulation (accum)
4.6 Application of Calibration to the Data
  4.6.1 Application of Calibration (applycal)
  4.6.2 Examine the Calibrated Data
  4.6.3 Resetting the Calibration Models (delmod and clearcal)
4.7 Other Calibration and UV-Plane Analysis Options
  4.7.1 Splitting out Calibrated uv data (split)
  4.7.2 Recalculation of uvw values (fixvis)
  4.7.3 Hanning smoothing of uv data (hanningsmooth)
  4.7.4 Model subtraction from uv data (uvsub)
  4.7.5 UV-Plane Continuum Subtraction (uvcontsub)
  4.7.6 Spectral regridding of the MS (cvel)
  4.7.7 UV-Plane Model Fitting (uvmodelfit)
  4.7.8 Reweighing visibilities based on their scatter (statwgt)
4.8 Examples of Calibration

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Chapter 4Synthesis Calibration

Chapter 4
Synthesis Calibration