VLA > VLA Data Archive

# VLA Data Archive

### Locating and unlocking data

Newly observed data are transferred to the archive and available for retrieval to those with the appropriate privileges approximately 10 minutes after the end of the observations.

While we are adding a new capability to the archive data retrieval process, making available the shipping of large amounts of data on hard disks instead of copying over the internet, the logical order of the web interface is mangled. Please be aware that information entered on leading pages may be ignored later on. We are in the process of fixing this, but we figured that offering the shipment of disks was more urgent than delaying it for a few months for a restructuring of our archive web pages. For further information we refer to our Data Shipment Policy.

The online archive contains all VLA data since observing started in 1976, and its contents are available via the Archive Access Tool (AAT), which provides both a basic search and an advanced search.  This interface provides a basic data retrieval tool if you know the program code of your observations. It also provides an advanced query tool which enables searches based on a large number of user-specified criteria. Data can be downloaded via standard ftp protocols and via shipment of physical hard disks, subject to the conditions of our

With the exception of some rapid response and large proposals, VLA 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

VLA data taken after January, 2010, when the transition to the WIDAR correlator took place, are stored in the Science Data Model (SDM) format that is used by both the VLA and ALMA. VLA data are available through the AAT in the following formats:

• In the native Science Data Model (SDM) format.
• As a CASA Measurement Set (MS) created from the SDM, which may be averaged in frequency and/or time, to be used with CASA.

Since the start of D configuration in 2013 the archive also contains products of the calibration pipeline.  Though eventually these data will be made accessible through the AAT as well, for the time being they have to be requested through the

• When requesting MS format, which consists of a directory with sub-directories, we recommend requesting tar-format. This will collect the whole directory structure in a single file for easy retrieval.
wget -r -w 10 -c --user=USERNAME --password=PASSWORD -e robots=off https://archive.nrao.edu/secured/USERNAME

Some archival data have known problems which, together with the possible fix, are listed at the archive issues page.  Delivery of data in the UVFITS format has been discontinued in June 2013. Instructions to create UVFITS from the SDM or CASA format are given below.

### Creating UVFITS Formatted Files

#### Using the SDM format (for use in AIPS)

Observers who have installed Obit can convert SDM data directly into UVFITS or load SDM data directly into AIPS.  Note that Obit cannot convert complex correlator modes into a single UVFITS/AIPS file, but plain continuum or simple line data is not a problem.

The latest version of Obit can be found by scrolling to the bottom of the Obit distribution page. Be aware that Obit is a bit harder to install on Macs than on Linux architectures.

To convert SDM data into UVFITS use these steps:

2. using Obit run the task "ASDMList" to obtain a correlator configuration listing for selection
3. using Obit run the task "BDFIn" to specify the output UVFITS file name

Alternatively use the AIPS path below and write out the file using the AIPS task "FITAB" (or FITTP)

To load SDM data into AIPS use these steps: