Using the VLA

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VLA capabilities September 2013 - January 2014

1. Obtaining Observing Time on the VLA

Observing time on the VLA is available to all researchers, regardless of nationality or location of institution. There are no quotas or reserved blocks of time. The allocation of observing time on the VLA is based upon the submission of a VLA Observing Proposal using the on-line Proposal Submission Tool available via the NRAO Interactive Service web page, at The on-line tool permits the detailed construction of a cover sheet specifying the requested observations, using a set of on-line forms, and uploading of a pdf-format scientific and technical justification to accompany the cover information.

It is also possible to obtain VLA observing time by proposing to NASA missions, under cooperation agreements established between NRAO and those missions. Currently, such programs exist for the Chandra and Fermi missions. Astronomers interested in those joint programs should consult the relevant mission proposal calls for more information.

Students planning to use the VLA for their PhD dissertation must submit a "Plan of Dissertation Research" of no more than 1000 words with their first proposal. This plan can be referred to in later proposals. At a minimum the plan should contain a thesis time line and an estimate of the level of VLA resources needed. The plan provides some assurance against a dissertation being impaired by an adverse review of a proposal when the full scope of the thesis is not seen. The plan can be submitted via NRAO Interactive Services. Students are reminded to submit their plan comfortably in advance of the proposal deadline. New thesis plans must be in pdf format so science reviewers can easily access the plans. Students who have not yet graduated but have active plans on file should consider updating those plans to a pdf format if they are not already in that form.

Time on the VLA is scheduled on a semester basis, with each semester lasting six months. Proposal deadlines are 5pm (1700) Eastern Time on February 1 and August 1. If the deadline falls on a holiday or weekend, it is extended to the next working day. The February 1 proposal deadline nominally covers time to be scheduled during the following August through January, and the August 1 deadline is for time to be scheduled from February through July. At either deadline requests can be made for a VLA configuration linked to a future deadline.

Proposals are evaluated on the basis of scientific merit by eight Science Review Panels (SRPs). The proposals are also reviewed for technical feasibility by NRAO staff. The SRP's comments and linear-rank scores are strongly advisory to the Time Allocation Committee (TAC). The scores and comments from both the SRPs and TAC are passed on to the proposers soon after each meeting of the TAC (twice yearly) and prior to the next proposal submission deadline. See for a detailed description of the proposal evaluation and time allocation process.

Because of competition, even highly ranked proposals are not guaranteed to receive observing time. This is particularly true for proposals that concentrate on objects in the LST ranges occupied by popular targets such as the Galactic Center or the Virgo Cluster. Daytime observing will also continue to be limited by VLA enhancement activities throughout 2013.

2. Director's Discretionary Time

The NRAO has established two categories of proposals for Director's Discretionary Time (DDT). DDT is limited to a maximum of about 5% of the total observing time on the VLA. All DDT proposals must be submitted using the standard NRAO procedures, using the on-line proposal tool. Proposals submitted by any other means (e.g., phone calls, e-mails, faxes, word-of-mouth) will be not be considered.

1. DDT Target of Opportunity. Target of Opportunity (ToO) proposals are for unexpected or unpredicted phenomena such as extreme X-ray or radio flares. ToO proposals are evaluated rapidly, with scheduling done as quickly as possible and as warranted by the nature of the transient phenomenon. ToO proposals are evaluated on the basis of scientific merit by Observatory scientific staff. Those staff also asses the technical feasibility of the ToO proposals. The proprietary period for data obtained by ToO proposals will be assessed on a case-by-case basis but will be no more than six months.

2. DDT Exploratory Time. Exploratory Time proposals are normally for requests of small amounts of time, typically a few hours or less, in response to a recent discovery, possibly to facilitate future submission of a larger proposal. In general, there will not be a need for immediate scheduling with these proposals, but they may need to be observed in the current VLA configuration rather than waiting 16 months. The possibility that a proposer forgets about or misses an NRAO proposal deadline, or just discovered that he/she was granted time for a particular source on some other telescope, will not constitute sufficient justification for granting observing time by this process. Thus, Exploratory Time proposals must include a clear description of why the proposal could not have been submitted for normal review at a previous NRAO proposal deadline, and why it should not wait for the next proposal deadline. Exploratory Time proposals are evaluated on the basis of scientific merit by Observatory scientific staff. Those staff also asses the technical feasibility of the Exploratory Time proposals. Notification of the disposition of an Exploratory Time proposal normally will be within three weeks of receipt of the proposal; some of these proposals may be put in a queue such that they may or may not be observed. The proprietary period for data obtained by Exploratory Time proposals normally will be six months.

3. Helpdesk

Assistance with proposal submission, observation preparation, archive access, and data reduction using both CASA and AIPS is available through the NRAO Helpdesk.  We try our best to get back to you within one working day, although it can take repeated back-and-forth communication to completely resolve your question.  You log on with your user name and password.  If you don't have an account you will be given the opportunity to register.

4. Observation Preparation

To observe with the VLA on an approved proposal, scheduling blocks must be prepared using the "Observation Preparation Tool," or OPT. The OPT is available at:

Once an observing proposal has been approved for scheduling, about 2-4 weeks before the relevant array configuration in the observing semester, the details of the proposal will appear as a project with program blocks in the OPT. Source and resource catalogs will also be populated as much as possible. The proposers will be notified by email when this has occurred, and when the scheduling queue will be accepting scheduling blocks. Please adhere to the current restrictions posted on;  things do change and the current restrictions page reflects our latest requirements for accepting scheduling blocks.

After consulting the documentation, any remaining questions or help required in making scheduling blocks can be directed to the NRAO Helpdesk at using your user account.

5. Dynamic and Fixed-Date Scheduling

Most projects on the VLA are observed dynamically, based on a combination of the scheduling priority and the expected properties of the array and the weather. Such dynamic scheduling enhances science data quality and the array's ability to discharge time-sensitive science. Some projects requiring coordinated observations with other telescopes will be scheduled on a fixed date.

For further information, see the scheduling officers' home page at

6. The Observations and Remote Observing

Since most VLA observations are carried out dynamically it is in general neither necessary, nor practical, for observers to be present during their observations. However, there can be considerable benefits to observers who come to Socorro to reduce and analyze their data in terms of interactions and discussions with NRAO staff. See Reservations for the VLA site and/or SOC for information on coming to and staying in Socorro.

For those who choose to process their data at home, the data can be retrieved from the VLA online archive by using the NRAO Interactive Services login from the archive web page.  Depending on the size of your data and the speed of your transmission you may choose to retrieve your data online or have us mail you a disk containing your data.

For more information we refer to the VLA archive web page and our Data Shipment Policy.

7. Data Access

The online archive contains all VLA data since observing started in 1976, and its contents are available via the Archive Access Tool (AAT) . 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 harddisks, subject to the conditions of our disk shipment policy. 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). Proprietary data may be downloaded by any member of the observing team by logging in to the AAT with the user account or by making use of the project key (see The Observations and Remote Observing).

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 pipeline calibrated MS.  Though eventually these data will be made accessible through the AAT as well, for the time being they have to be requested through our helpdesk

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 or loading data into AIPS using the SDM format

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:

  1. download the SDM format from the archive
  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:

  1. download the SDM format from the archive
  2. using AIPS run the task "BDFLIST" to obtain a correlator configuration listing for selection
  3. using AIPS run the task "BDF2AIPS" to specify the output AIPS file name and disk number

Creating UVFITS formatted data using CASA

To produce UVFITS formated data using CASA take the following steps:

  1. download the data from the archive either in SDM or in MS format
  2. Start CASA
  3. Unless you downloaded MS data, convert the SDM formatted data to MS using the CASA task importvla
  4. Apply the requantizer gains as described in the section on 3-bit data observing in the VLA Observing Guide
  5. Convert this MS file to UVFITS format using the CASA task exportuvfits

8. Data Processing

The primary data reduction package for the VLA is the CASA (Common Astronomy Software Applications) package, which is also used for ALMA.  See for more information on the latest release.

It is possible to reduce VLA data taken in all correlator modes that are offered for general observing using CASA.  More complex correlator set-ups are generally better handled by CASA, and advanced imaging algorithms are available in CASA.  The VLA calibration pipeline uses CASA.

The Astronomical Image Processing System (AIPS) can reduce all observations made with simple correlator set-ups (e.g., identical spw bandwidths and channel widths throughout).  AIPS is currently required for the reduction and analysis of phased-array VLA observations for VLBI and low-band observations (P-band, 230-470 MHz). NRAO will continue to support AIPS for the foreseeable future, at least until VLBI functionality and the full data path for frequencies below 500 MHz have been incorporated into CASA.  See for more details.

9. Travel Support for Visiting the SOC and VLA

Travel support is available for U.S.-based observers to travel to NRAO to observe and/or reduce data.  Please see Travel Support for NRAO Observing Runs and Data Reduction for Non-NRAO Employees for details of eligibility and how to claim reimbursement.

10. Student Observing Support Program

In addition to travel support for individual data reduction visits NRAO maintains a program to support research by students, both graduate and undergraduate, at U.S. universities and colleges. Regular and Large proposals submitted for the VLA, VLBA, and GBT, and any combination of these telescopes, are eligible. New applications to the program may be submitted along with new observing proposals at any proposal deadline. Details of this program can be found at

11. Computing at the SOC

A primary goal of the computing environment at the SOC is to allow every user full access to a workstation during his/her visit. There are 10 public workstations available at the SOC for full-time data reduction by visitors. They are mostly two-processor, 8 core , 2.4-GHz PCs with 24GB of memory and 4TB of local disk running Linux.

For hardcopy, we have a number of high volume B&W laser printers, two color Postscript laser printers which can reproduce on both paper and transparencies, and one wide-bed color printer.

Visitors should reserve time on these workstations when they make their travel arrangements at (see also Reservations for the VLA site and/or SOC). Note that users may request remote access to the visitor machines as well, without actually visiting the SOC.  Remote reservations are subject to availability. Please contact the computing helpdesk (e-mail to, extension 7213, office 262) for further information about this and any other computing assistance while at the SOC.

For a more complete description of computing facilities at the SOC, see

12. Reservations for the VLA site and/or SOC

Accommodation for visitors is no longer available at the VLA site. Observers wishing to be present for their observations should stay in the nearby towns of Magdalena or Datil.

Reservations must be made at least 1 week prior to your visit to the NRAO/NM, and 2 weeks' notice is preferred, through the online form at Computing requirements and the level of staff assistance needed must be specified through the online form.

First-time visiting students will be allowed to come to the NRAO/NM for observations or data reduction only if they are accompanied by their faculty advisor, an experienced collaborator, or if they have an NRAO staff collaborator.

13. Staying in Socorro

Visitors to Socorro can take advantage of the NRAO Guest House. This facility contains eight single, four double, and two two-bedroom apartments, plus a lounge/kitchen, and full laundry facilities. The Guest House is located on the New Mexico Tech (NMIMT) campus, a short walk from the DSOC. Reservations are made through the online registration form at the visitor registration form.

Since Socorro is located just off I-25, it has more than its share of motels.  Most are located on California Street, the main business thoroughfare.  Typical walking distance to NRAO is 20 - 30 minutes.

14. Help for Visitors to the VLA and SOC

We encourage observers to come to Socorro to calibrate and image their data. This is the best way to ensure the quickest turnaround and the best results from their observing. While in Socorro, each observer will interact with members of the SOC staff in accordance with his/her level of experience and the complexity of the observing program. If requested through the reservation form, the visiting observer will be guided through the steps of data calibration and imaging by a pre-arranged staff friend or scientific collaborator. A list of staff scientists and their interests can be found at The data analysts, computing helpdesk, and other staff are also available for consultation on AIPS and CASA procedures, and systems questions.

15. On-Line Information about the NRAO and the VLA

NRAO-wide information is available on the World Wide Web through your favorite Web browser at URL, and information specific to astronomers using the VLA may be found at  These pages are regularly updated by the NRAO staff.