There are three main advantages to using CASA 3.4 or later when reducing ALMA Cycle 0 data that may have originally been reduced in earlier versions of CASA:
- In CASA 3.4 the primary beam models used in CASA were improved to better account for the 12dB Gaussian taper of the 7 and 12 m antennas. This results in a primary beam that is 12.5% LARGER than the previous assumption. Thus for all mosaics or single fields with extended emission that have been primary beam corrected, the flux densities will be more accurate in CASA 3.4 and later versions.
- In CASA 3.4 it is possible for a user to derive all of the apriori calibration for Water Vapor Radiometry correction and System Temperature correction completely internally to CASA. Before this, these steps were performed outside of CASA in software not readily available to users (the resulting calibration tables are included in the data packages). The results should be very similar regardless of which method was used on a particular data set, so there is no particular advantage to redoing it.
- To improve the signal to noise of the bandpass solutions, it is possible in CASA 3.4 to smooth the data spectrally before determining the bandpass solution. This is a better alternative to smoothing the solutions after determination that could be used in earlier versions of CASA.
Additional information is available from the CASA release notes:
To see which version of CASA a particular dataset was reduced in, see the related helpdesk article: How can I tell from the scripts provided as part of the Cycle 0 data products which version of CASA was used?