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Knowledgebase: Archive & Data Retrieval
How do I obtain a file of calibrated visibilities ("measurement set") for ALMA data?
Posted by Sarah Wood, Last modified by Sarah Wood on 11 October 2018 01:34 PM

ALMA raw data (asdm), data products (images or cubes), and auxiliary data (scripts, logs and quality assessment figures) are stored in the archive for each data delivery. This data includes the calibration and flagging tables. 

The FITS products delivered to the PIs are not complete. They mostly serve the purpose to show that the requested parameters are reached and do not always cover the full bandwidth, all spectral windows, or all fields. For many scientific use-cases, (re)imaging of the products will be required. Users will need the calibrated visibilities if they wish to re-calibrate or re-image the data.

Calibrated visibilities can be easily recreated by downloading the products and the raw data tar files and then running the scriptForPI.py using the correct CASA version. This procedure is also specified in the ALMA QA2 Data Products document for each cycle, located here: http://almascience.org/processing/qa2-data-products

Download all tar files for a given delivery from the ALMA Science Archive and untar them. Then change into the "script" directory with the python scripts:

cd */*/*/*/script

Start the correct version of casa (or "casa --pipeline" for data reduced using the ALMA pipeline) What CASA version was used for QA2? and type

>execfile('scriptForPI.py')

This will apply the flagging and calibration tables to the raw data and thus result in a MS ready for imaging. In some cases a specific version of CASA is required.

If the MOUS contains one in the scripts directory, the MS can then be processed with the commands in the "scriptForImaging.py" script. The "scriptForImaging.py" script may partially be interactive (for masking) and should be executed by copying and pasting the commands from the script to the casa prompt, rather than by the "exec file" command.
If there is no scriptForImaging.py, users can use the CASA Guides for guidance.

If your data was calibrated using the ALMA Science Pipeline, please see the CASA Guide for Imaging Pipeline Reprocessing or the document "ALMA Science Pipeline Quickstart Guide" available from the Documents page of ALMA Science Portal  for more information.

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