Initial calibrator models

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Initial calibrator models

The Calibrater tool requires an initial visibility estimate in the MODEL_DATA column before visibility-plane solvers can be used. This can be specified via a known external source model, expressed as a set of images and/or a list of component models, which are then transformed to the visibility-plane using the Imager.ft function. This initial model can also be derived by imaging the observed data directly, without calibration, where this is possible. Please consult the general Imaging chapter for instructions on forming images.

Alternatively, if the calibrator source is sufficiently compact, it can be regarded as a point source in the initial calibration iteration, or indeed throughout calibration. Upon initialization, the MODEL_DATA column already contains unit total intensity point source visibilities. If a subset of calibrators are to be used to set the flux density scale for the observation, the models for these should be set to the proper flux density. A facility exists to set standard source flux densities on the Baars or Perley-Taylor scales using the function Imager.setjy in the Imager tool. In this case, if the source is not recognized, it is set to an intial flux density of 1.0 Jy.

include 'imager.g'
imgr:=imager('polspec.ms')
imgr.setjy()                  # Set MODEL_DATA column to point-source models 
                              # (of correct flux density, if recognized):

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