Calibration Tasks

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4.1 Calibration Tasks

Alert: The calibration table format has changed in CASA 3.4. From now on, calibration tables are independent of the MS that they were created from and can be applied to any MS. We recommend using the new calibration table format throughout and recreate them when possible (only important when the user switches between CASA 3.3 to 3.4 during calibration). If absolutely necessary, old calibration tables can be converted to the new format using the task caltabconvert, but some information was not stored in the old tables and cannot be filled into the new tables. When old calibration tables were already applied with applycal, one can proceed with imaging as usual in any version of CASA and no action is needed.

The standard set of calibration solving tasks (to produce calibration tables) are:

bandpass — complex bandpass (B) calibration solving, including options for channel-binned or polynomial solutions (§ 4.4.2),
gaincal — complex gain (G,T) calibration solving, including options for time-binned or spline solutions (§ 4.4.3),
polcal — polarization calibration including leakage and angle (§ 4.4.5),
blcal — baseline-based complex gain or bandpass calibration (§ 4.4.6).

There are helper tasks to create, manipulate, and explore calibration tables:

accum — Accumulate incremental calibration solutions into a cumulative cal table (§ 4.5.5),
applycal — Apply calculated calibration solutions (§ 4.6.1),
clearcal — Re-initialize the calibration for a visibility dataset (§ 4.6.3),
fluxscale — Bootstrap the flux density scale from standard calibration sources (§ 4.4.4),
listcal — List calibration solutions (§ 4.5.2),
plotcal — Plot calibration solutions (§ 4.5.1),
setjy — Compute model visibilities with the correct flux density for a specified source (§ 4.3.4),
smoothcal — Smooth calibration solutions derived from one or more sources (§ 4.5.4),
split — Write out new MS containing calibrated data from a subset of the original MS (§ 4.7.1).

There are some development versions of calibration and utility tasks that are recently added to the suite:

calstat — Statistics of calibration solutions (§ 4.5.3),
cvel — Regrid a spectral MS onto a new frequency channel system (§ 4.7.6),
gencal — Create a calibration table from lists, including options for delays, antenna position errors, and amplitude and phase adjustment (§ 4.3.5),
wvrgcal — Generate a gain table based on Water Vapour Radiometer data (for ALMA use - § 4.3.7),
hanningsmooth — Apply a Hanning smoothing filter to spectral-line uv data (§ 4.7.3),
uvcontsub — Carry out uv-plane continuum fitting and subtraction (§ 4.7.5),
uvmodelfit — Fit a component source model to the uv data (§ 4.7.7),
uvsub — Subtract the transform of a model image from the uv data (§ 4.7.4),
statwt — Recalcuate the data weights based on their scatter (§ 4.7.8).

These are not yet full-featured, and may have only rudimentary controls and options.

The following sections outline the use of these tasks in standard calibration processes.

Information on other useful tasks and parameter setting can be found in:

listobs — summary of a MS (§ 2.2.6),
listvis — list data in a MS (§ 2.2.7),
plotms — prototype next-generation X-Y plotting and editing (§ 3.3.1),
plotxy — previous generation X-Y plotting and editing (§ 3.3.2),
plotweather — plot the weather information of an MS and calculate atmospheric opacities (§ 4.3.3.1),
tflagdata — non-interactive data flagging (§ 3.4),
data selection — general data selection syntax (§ 2.3).

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