Sub-parameter scaletype

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5.3.4.5 Sub-parameter scaletype

Inside the Toolkit:

The im.setmfcontrol method gives more options for controlling the primary beam and noise across the image.

The scaletype parameter controls weighting of pixels in the image plane. This sub-parameter is activated for imagermode=’mosaic’.

The default scaletype=’PBCOR’ scales the image to have the correct flux scale across it (out to the beam level cutoff minpb). This means that the noise level will vary across the image, being increased by the inverse of the weighted primary beam responses that are used to rescale the fluxes. This option should be used with care, particularly if your data has very different exposure times (and hence intrinsic noise levels) between the mosaic fields.

If scaletype=’SAULT’ then the image will be scaled so as to have constant noise across it. This means that the point source response function varies across the image attenuated by the weighted primary beam(s). However, this response is output in the .flux image and can be later used to correct this.

Note that this scaling as a function of position in the image occurs after the weighting of mosaic fields specified by mosweight and implied by the gridding weights (ftmachine and weighting).

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