Science Reference Data Products (SRDP) for the VLA

The SRDP initiative was created to improve the user experience for radio interferometry data from the VLA by providing users with calibrated data and reference images to use in their science. Initially a development project, SRDP is now part of standard pipeline operations at the NRAO for the VLA.

What is it?

All science observations from the VLA are run automatically through the VLA-CASA data reduction pipeline which includes standard calibration, continuum and spectral line imaging, and self-calibration when possible. Continuum imaging is performed on the calibrated data on a per-target, per execution block basis. The calibration and imaging are quality assessed by NRAO staff, who will re-run the pipeline with additional flagging or modified parameters if necessary to provide higher quality data for imaging. Quality-assessed calibration products and images are ingested into the NRAO data archive and are available for download shortly thereafter (see below). These products are produced per execution block. The calibration products and references images are provided on a best-efforts basis, and may be useful for science depending on individual science goals. As we learn more about the data products over time, quality assessment and data handling practices may evolve.

 

What qualifies?

Quality Assessed calibration and imaging is performed for the following:

  • L,S,C,X,Ku,K,Ka,Q bands (including multi-band observations)
  • both continuum projects and spectral line observations
  • subarray observations
  • observations must include a flux density scale calibrator for each correlator tuning used for science, and properly set scan intents in the Observation Preparation Tool (OPT)

What doesn't qualify?

  • P band or 4-band observations
  • pulsar timing observations
  • VLBI observations with the VLA (including Y1 and Y3)
  • polarization calibration, though Stokes I calibration will be performed on polarimetric data sets that satisfy the conditions above. See the Karl G Jansky VLA CASAguides for guidance on how to complete polarization calibration starting with standard pipeline products

 

What data are available at the NRAO Science Data Archive (data.nrao.edu)?

  • Raw data are ingested into the archive immediately upon observation. All data are subject to a 2-year proprietary period.
  • Calibrated products from the quality-assessed pipeline calibration are available only if the pipeline run was successful--- denoted by a "1" listed under the Cals column in the archive for the observation. Quality assessment (QA) notes regarding the pipeline run may also be available. If multiple calibration versions are listed, "1" contains the most recent (recommended) calibration.
  • Calibration tables including self-calibration (when applicable, only on/after 2025-02-27), the final flag version, and the pipeline weblog are available by downloading the calibration tar file found under the "Cals" column in the archive.
  • Calibrated measurement sets will be generated on-the-fly when requested by restoring the calibration tables with CASA. The time for a calibrated measurement set to be available depends strongly on the size of the dataset. The restoration process applies Hanning smoothing, reapplies pipeline flagging, applies the archived calibration tables, and runs statistical weighting.
  • For recent data, images from the basic pipeline are available, as well as self-calibrated images (when applicable) which will have "selfcal" in the product name.

 

How do I access Science Reference Data Products?

1.   Go to https://data.nrao.edu
1a. Login for access to proprietary data**
2.   Search for some data (e.g. project code, target name, position/radius). One can View Projects, individual Observations, or Images depending on the tab selected.
3a. For calibration data, click the '+' to see more detail about a project or observation. To access a calibrated data set, click the "Select for Download" button to the left of the observation, then click "Download". To access the most recent calibration tables and pipeline weblog, click the "1" under "Cals" then click "Download".
3b. To download images, click "Select for Download" then click "Download". Images are also viewable with CARTA through the archive: click "View in CARTA".

** Logins are only required if a user wishes to access proprietary data or to request local delivery of data to the NRAO Lustre file system. Select the "NRAO" account service for VLA data. Accounts can be created at my.nrao.edu.

Help with SRDP products:

For further questions about the VLA SRDPs, please contact the NRAO Helpdesk through the VLA Data Products department.

Connect with NRAO

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