ALCHEMI Data Reduction Group: Automasking

TIP Last Modified: JeffMangum - 06 September 2018

Table of Contents:


Auto-mask in tclean (auto-multithresh) sometimes sets clean masks on sidelobes. This happens most frequently for Band 7 imaging with 12m-only data (see example image below.) This example used the automask parameters that are recommended in Automasking CASA Guides (, namely sidelobethreshold=2.0, noisethreshold=4.25, minbeamfrac=0.3, and lownoisethreshold=1.5 for cleaing to 2sigma.

Update [2018-10-27]. This problem still occurs in CASA 5.4. Automasking in CASA 5.4 makes virtually the same mask as shown in the attached image made with CASA 5.3. One has to either adjust the automasking parameters or add a manual mask to constrain the area for auto-masking.


Find a better set of parameters to avoid masking on sidelobes.

Current Status

-- JeffMangum - 2018-09-06
  • unsuccessful auto-mask:
Topic revision: r3 - 2018-10-27, KazushiSakamoto
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