Facilities > VLBA > Data Archive > VLBA Data Archive

VLBA Data Archive

by Emmanuel Momjian last modified Feb 24, 2021 by Frank Schinzel

Locating and unlocking data

The online archive contains all VLBA data since observing started in 1992, and its contents are available via the Archive Access Tool (AAT) or "legacy archive".  The AAT basic search provides a basic data retrieval tool if you know the program code of your observations. The AAT advanced search provides an advanced query tool which enables searches based on a large number of user-specified criteria. Proprietary data can be downloaded via secure https file transfer.  Public data can be downloaded via standard ftp protocols or via https file transfer.  On request, NRAO will ship data on physical hard disks, subject to the conditions of our Data Shipment PolicyNOTE: The NRAO has temporarily suspended the option to ship data on hard disks during the COVID-19 pandemic.

Newly correlated VLBA data are transferred to the archive and made available for retrieval to those with the appropriate privileges.  With the exception of some rapid response and large proposals, VLBA data associated with a given proposal normally are restricted to proprietary use by the proposing team for a period of 12 months from the date of the last observation in a proposal (Note: data taken more than 12 months previously may still be proprietary, if additional data for the same proposal have been taken within the last 12 months).  Any member of the observing team can unlock proprietary data by signing in with their my.nrao.edu user ID and password, using the link in the 'unlock my data' box in the upper right of the search page.

Alternatively, the Data Analysts will send out the Locked Project Access Key upon request.  (Please use the NRAO Helpdesk for these requests.)  For projects which did not go through the NRAO proposal process (e.g., those starting with S) this is the only way to unlock data.

If you were not listed on the original proposal, you must first obtain permission from the PI, who in turn, must contact us through the NRAO Helpdesk to allow your access to the proprietary data.

Refer to the NRAO Data Archive Policy for more information regarding proprietary data.

 

Data Formats and Data Retrieval

All VLBA data are stored in FITS-IDI format.  Observations correlated with the legacy hardware correlator will have a .uvfits extension.  All observations correlated with the DIFX software correlator will have a .idifits extension. 

Please note:

  • It is not currently possible to retrieve Measurement Set (MS) format data for VLBA observations.  Users who wish to use CASA for the data calibration will need to create MS files themselves with the CASA task importfitsidi.  See below for more information on using CASA for VLBA data.
  • It is not currently possible to create tar-format files from the FITS-IDI files.  However, FIT-IDI files are already self-contained single files, unlike the directory-structured MS and SDM files for VLA data.  Therefore, downloading VLBA data is usually straight forward and users can easily retrieve their data using the link provided in the email from the archive.
  • An alternative way to retrieve data is to use wget.  In the following, substitute the username and password from the e-mail announcing that your data has been downloaded:
wget -r -w 10 -c --user=USERNAME --password=PASSWORD -e robots=off https://archive.nrao.edu/secured/USERNAME
  • It is also possible to ship data on hard disks rather than retrieving the data over the internet.  However, the number of disks available for shipping is limited and this method should be reserved for very large data sets where downloading over the internet is impractical.  For further information, refer to the NRAO Data Shipment PolicyNote that NRAO is not shipping hard disks during the COVID-19 pandemic.

Some archival data have known problems which, together with the possible fix, are listed at the archive issues page.

 

"New Archive"

NRAO continues to recommend using the "legacy archive" to retrieve data from all VLBA and HSA observations. 

The NRAO is currently developing a new portal for accessing data from VLA and VLBA observations.  Observers are welcome to try using the "new archive" to retrieve their VLBA data.  However, the new archive does not yet have access to all VLBA data.  In particular, HSA observations and data in the Mark4 format are likely to be problematic in the new archive. Also, observations that used multiple receivers in a single observation (e.g., S/X projects, or observations that switched between two or more receivers) may have only a single band listed in the new archive. 

The new archive will eventually become the only tool for accessing all VLBA and VLA data.  Any observers who decide to try using the new archive while it is under development and find problems are asked to report their issues to the NRAO via the helpdesk


Using CASA with VLBA Data

NRAO continues to recommend using AIPS for calibrating all VLBA observations.  However, CASA versions 5.3 and later contain tools for calibrating basic continuum VLBI data.

      NRAO staff are still evaluating CASA's readiness for calibration of VLBA data.  Observers who wish to use CASA for VLBA data calibration and analysis are warned to be cautious and make certain they have the most recent CASA version, as it will contain the most up-to-date VLBI tools.  Also, it is recommended to use CASA 5.X for VLBI data due to the fact that the plotcal task is not available in CASA 6.X. 

      CASA importfitsidi does not currently import the VLBA gain curve table.  Users will need to convert the gain curve table to a CASA-readable table using an external script (gc2.py, written by Mark Kettenis and available from JIVE’s CASA VLBI Github repository).  For more information, see the VLBI CASA Guides page.