Mosaic and JvM factor
Keywords: imager

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Mosaic and JvM factor

By construction, the various fields covered in a mosaic have different coverages, and thus different synthesized beams. Furthermore, mosaic covers wider fields, so the impact of frequency variable angular resolution is more important than in single fields.

Yet, the mosaic is restored with a unique Clean beam. This situation leads to a mismatch between the use Clean beam and the dirty beams in some or even most of the fields. Furthermore, because Mosaics often use short spacings (see Section ), the dirty beams often present a wide ``plateau'' that is not well fit by a Gaussian Clean beam. These are situations which are prone to lead to inaccurate large scale flux restoration, because the Clean beam and dirty beams area do not match.

To minimize these issues, it is recommended in [rgb]1,0,0IMAGER to use the magenta`FIT /JVM_FACTOR` and magenta`UV_RESTORE` commands that correct this mismatch to first order by re-scaling the residual by the Clean to Dirty beam ratio, the so-called blue`JvM factor` (()). Only do so once you are satisfied with your deconvolution, as magenta`UV_RESTORE` is often time consuming on Mosaics.

Next: Short and Zero spacings Up: Wide-field imaging and deconvolution Previous: Typical use Contents Index