Release Notes

Summary of new features in this release of CASA

CASA 5.1.2 vs. 5.1.1

The CASA 5.1.2 release builds on CASA 5.1 and is mostly intended as a patch for the VLA pipeline. Changes compared to the previous  CASA 5.1.1 patch include:

  • reordering the INTENTs for VLA data, to accommodate older data that have TARGET intents for requantizer scans;
  • fix to task plotweather, to close all table calls properly when no WEATHER data is available in the MS;
  • enabled the support of Total Electron Content (TEC) corrections in the VLA pipeline tasks;
  • Pipeline task hif_makeimlist: for data sets where the central channel of a spw is flagged, the synthesized beam is now derived from a non-flagged channel nearest to the central flagged channel. 

 

The following are the release notes for CASA 5.1: 

Documentation

  • We continue to update CASA Docs but are still in a transitioning phase for task and tool descriptions. Please use the inline help if the task or tool description is not yet available on CASA Docs

 

Data Import/Export

  • The matrix syntax in FITS files has been modernised and now follows standard 3.0. The way exportfits handles PC matrix convention is updated:

    • gridline rotation as seen in casaViewer is now consistent and correct in both casa image format and fits image format.

    • pc matrix convention "PCi_j" is now the convention and the casaViewer now shows results consistent with ds9.

 

MS Viewing, Editing, Manipulation

  • The CASA 5.0 task visstat has been renamed visstatold for CASA 5.1. The CASA 5.0 task visstat2 has been renamed visstat for CASA 5.1, although it is still available with the name visstat2
  • cvel2 & mstransform: regridding (regridms=True) has been corrected to follow the same procedure as in tclean. mstransform does not any longer pre-average channels when the ratio between the output and input width is >2.

 

Calibration

  • Ionospheric Total Electrion Content (TEC) corrections (low frequency cm observing):
    • TEC "at site" plot now stored in file.
    • tec_maps.create0 now generates (non-interactive) plot file
  • Reference antenna selection:
    • The gaincal task now supports "strict" refant application via a new refantmode parameter, which will flag solutions timestamps (per spw) if the specified refant is unavailable (flagged or absent). Useful for polarimetry where refant cross-hand phase stability is important.
    • New 'rerefant' task which permits revising the refant on an existing caltable.
  • Flux scaling: in the CASA 5.0 "Known Issues", a bug was reported for fluxscale, where it generated incorrect results if the flux density calibrator field, as specified in the reference parameter, was also specified among the other calibrators in the transfer parameter. This bug has been fixed, in that the reference calibrator that is also listed in the transfer parameter will now be excluded from the scaling process.

 

Imaging

  • Automasking:
    • The growiterations subparameter has been added for multithreshold automasking in tclean (usemask='auto-multithresh') to control the number of iterations used by binary dilation to expand the mask into low signal-to-noise regions. Lowering this number can help to improve the processing speed of tclean particularly when it involves a large cube, but may lead to less effective masking of extended emission. The default has been selected to optimize masking of extended emission. Some experimentation may be needed to determine the most effective lower value for your purposes.
    • An experimental feature has been added to auto-multithresh algorithm (usemask='auto-multithresh') to mask absorption, which is controlled by the sub-parameter negativethreshold. This value is a signal-to-noise based parameter similar to the noisethreshold and lownoisethreshold parameters in the auto-multithresh algorithm. Currently, the masks produced using this threshold are not independent of the emission threshold-based masks, so use of this parameter may lead to masking of low-lying positive emission near absorption. This feature assumes that the data have been continuum subtracted.

 

Single Dish

  • ATNF Spectral Analysis Package (ASAP) is removed from CASA. The sd tool and the following single dish tasks are removed, sdaverageoldsdbaselineoldsdbaseline2oldsdcaloldsdcal2oldsdcoaddoldsdfitoldsdflagmanageroldsdflagoldsdgridoldsdlistoldsdmatholdsdplotoldsdreduceoldsdsaveoldsdscaleold, and sdstatold.
  • The sdimprocess task is renamed sdfixscan. Also, mode='basketweave' and 'press' are renamed 'FFT_mask' and 'model', respectively.
  • The sdimaging task now supports several types of projections. Currently, SIN (slant orthographic; default), CAR (plate carree), TAN (gnomonic), and SFL (Sanson-Flamsteed) are available.
  • The sdimaging task now supports overwriting brightnessunit of the CASA image. Currently, 'K' (Kelvin) and 'Jy/beam' are available.
  • The parameter verbose is available in sdbaseline task when blfunc='variable'. When verbose=False (default), logging of per spectrum fitting parameters is supressed.
  • The sdgaincal task now allows to specify a list of caltables to be applied on-the-fly during computing calibration factor using the parameter applytable. You can specify spwmap and interpolation method (interp) for each caltables specified by applytable. Syntax for spwmap and interp is same as applycal task.
  • The sdcal and sdgaincal tasks support calibration of single polarization data.

 

Tools

  • The ms tool has new functions ending in "2" (for example, getdata2), which change the underlying implementation to a newer infrastructure but have the same arguments and functionality. The old functions will eventually be deprecated and replaced by the new ones.
  • There is a new msmd tool method timesforspw() to retrieve all time stamps associated with a specified spectral window

 

Other changes

  • The use of the ‘casadef’ module is deprecated. The CASA version information has been moved to the ‘Class utilities (cu)’ module. This module contains functions cu.version and cu.compare_version to retrieve the CASA version number and compare version numbers. The subversion information that is found in the ‘casadef’ module is no longer up to date. CASA now uses git for source code version control and no analogous git state is available. The ‘casadef’ module will be removed in CASA 5.2 or CASA 5.3 depending on the timing of these releases.