National Radio
Astronomy Observatory

5.2.11 Parameter weighting

In order to image your data, we must have a map from the visibilities to the image. Part of that map, which is effectively a convolution, is the weights by which each visibility is multiplied before gridding. The first factor in the weighting is the “noise” in that visibility, represented by the data weights in the MS (which is calibrated along with the visibility data). The weighting function can also depend upon the uv locus of that visibility (e.g. a “taper” to change resolution). This is actually controlled by the uvtaper parameter (see § 5.2.10). The weighting matrix also includes the convolution kernel that distributes that visibility onto the uv-plane during gridding before Fourier transforming to make the image of the sky. This depends upon the density of visibilities in the uv-plane (e.g. “natural”, “uniform”, “robust” weighting).

The user has control over all of these.

ALERT: You can find a weighting description in the online User Reference Manual at:

http://casa.nrao.edu/docs/casaref/imager.weight.html

The weighting parameter expands the menu to include various sub-parameters depending upon the mode chosen:

More information about CASA may be found at the CASA web page

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