Facilities > VLA > Science > Shared Risk Observing 2013A - January 25 - August 19, 2013

Shared Risk Observing 2013A - January 25 - August 19, 2013

by Gustaaf Van Moorsel last modified Sep 03, 2013
Shared Risk Observing 2013A - January 25 - August 19, 2013

The general capabilities of the Karl G. Jansky Very Large Array (VLA) have been extensively upgraded as stated in the August 1, 2012 call for proposals.  By January 2013, all antennas and receiver bands will be upgraded and extensive testing of the WIDAR correlator will have been done.  The last of the L (1-2 GHz), S (2-4 GHz), X (8-12 GHz) and Ku (12-18 GHz) bands will be installed by late 2012.  Further, the 3-bit sampler system, enabling up to 8 GHz of simultaneous bandwidth at high frequencies, will be installed.

The general capabilities for the 2013A semester (January 25 - August 19, 2013) are extensive with flexible tuning of sub-band spectral line windows using the 8-bit samplers (enabling up to 2 GHz total bandwidth), use of the 3-bit samplers at higher frequencies in a mode that is suitable for wide-band continuum and extragalactic lines and line searches, use of up to 3 independent sub-arrays and a phased array capability for VLBI.  A summary of the general observing capabilities, as described in the 2013A Call for Proposals, is given below:

Capability Description
8-bit samplers
  • Standard default set-ups for 2 GHz bandwidth (1 GHz BW at L-band) continuum observations (16 x 128 MHz sub-bands)
  • Up to 32 independent & flexibly tunable sub-bands for spectral line observing
  • Single, dual & full polarization
  • Spectral channels as narrow as 1.9 Hz (single polarization), up to 16,384 channels
3-bit samplers
  • Standard default set-ups for 8 GHz bandwidth continuum observations at K/Ka/Q bands
  • 64 contiguous 128 MHz sub-bands
  • Spectral resolution suitable for extragalactic lines and line searches
  • Single, dual & full polarization
  • Spectral channels widths of 2 MHz (full pol), 1 MHz (dual pol), 0.5 MHz (single pol)
Sub-arrays
  • Up to 3 independent sub-arrays using standard 8-bit continuum set-ups (2 GHz BW)

Both single pointing and mosaics with discrete, multiple, field centers will be supported. Data rates of up to 20 MB/s (72 GB/hour) will be available to all users, combined with correlator integration time limits per band and per configuration, as described in the OSS.

Despite these increased capabilities, there remain areas where it is possible to increase the scientific potential of the VLA and VLBA.  Thus, we continue to offer shared risk programs to our user community for those who would like to push the capabilities beyond those offered for general use.  Up to 25% of observing hours will be made available to Shared Risk observations during semester 2013A; the actual fraction of time assigned will depend upon demand, the quality of the proposed science as judged via the peer-review process, and upon the quality of the technical support offered to the VLA project, as determined by NRAO.

As stated in the call for proposals, we will offer two options:

Shared Risk Observing:

This program will allow users access to capabilities that can be set up via the OPT and run through the dynamic scheduler (without intervention), but are not well tested. Shared Risk observers will automatically receive one hour of test time to verify their correlator set-up and observing procedure.  Capabilities that would fall under the Shared Risk Observing program include, e.g.,

  • Dump times as short as 50 ms with data rates as high as 60 MB/s;
  • More flexible baseline board stacking using baseline boards stacked by something other than a power of 2 (e.g. using 3, 5, 7, 9 baseline boards to support a single sub-band (spectral line window) in order to more closely match the resolution and bandwidth requirements to the science goals or to use the correlator more efficiently);
  • A limited and relatively simple spectral sweep mode, using recirculation  to provide higher spectral resolution over 2 GHz of bandwidth;
  • Use of the 3-bit sampler system at C (4-8 GHz), X (8-12 GHz) and Ku (12-18 GHz) bands.    Before deciding to use the 3-bit samplers at these bands, consider the following:
    • The 3-bit sampler system is not as reliable as the 8-bit samplers.  This is inherent in the sampler hardware.  With a factor of 4 increase in bandwidth, the RMS noise only improves by a factor of about 1.6 (not 2 as might be expected).  Further, the 3-bit sampler system requires increased overhead time for set-up and calibration during the observations.  Thus, the potential improvement in the RMS noise at C, X and Ku bands, which only cover 4-6 GHz of total bandwidth) can be less than expected, and the impact of strong RFI on the RFI-free parts of the spectrum within these bands has not yet been fully evaluated with the 3-bit samplers;
    • Only 1-2 GHz bandwidth is available using the L (1-2 GHz) and S-band (2-4 GHz) feeds so there is no benefit from the use of the 3-bit samplers in these bands;
  • Use of the 3-bit sampler system with subbands narrower than 128 MHz.  All subbands within a baseband must be contiguous, and must have the same bandwidth;
  • Use of sub-arrays with the 3-bit sampler system;
  • Ability to mix 3- and 8-bit basebands (3-bit AC and 8-bit BD or vice versa), in the same correlator configuration.

A special  Shared-risk Resource Catalog Tool (SRCT) is available to assist with defining correlator set-ups for Shared Risk observing.

We expect that most Shared Risk programs will have none or only minor problems that can be corrected quickly.  However, if a preliminary test for a Shared Risk program fails and it becomes clear that detailed testing with PI expertise is needed, then the PI team must send an experienced member from their team to help troubleshoot the problem.  If adequate support from the PI team is not given, then the team will be deemed to have forfeited their time on the telescope.  The estimated duration of the time at NRAO is to be determined based on discussions with the NRAO staff and  management and the PI team.  However, the length of time required at NRAO, Socorro is expected to be on the order of a few weeks and not to exceed 1 month.

A Shared Risk Observing proposal is allowed an extra page compared with general observing proposals.   Shared Risk proposals should contain:

  1. A scientific justification, to be peer reviewed as part of NRAO's current time allocation process, submitted through the Proposal Submission Tool.  The correlator resources should be specified using the Shared-risk Resource Catalog Tool (SRCT) .
  2. A technical section describing how the team proposes to use their pre-observing test time and naming the personnel who will be available to come to the NRAO if the test runs into difficulties that cannot be addressed without further support.  This section will be reviewed by NRAO staff.
  3. A budget specifying the level and nature of any support that will be requested from NRAO if residency is required.  It is expected that NRAO will be able to provide accommodation in the NRAO Guest House, subject to availability.  Other support may be available separately through the NRAO Visitor's Program.

The acceptance of a Shared Risk proposal will depend on the merits of the scientific and technical justification.  A Shared Risk proposal must have a plan for who will be able to come to help if the pre-observing test is not successful.

Resident Shared Risk Observing:

This is an extension of the RSRO program offered during Early Science, which provides access to the extended capabilities of the VLA.  RSRO programs would require additional testing, in exchange for a period of residence to help commission those capabilities.  Capabilities that would fall under the RSRO program include (but are not limited to):

  • Correlator dump times shorter than 50 ms;
  • Data rates up to 140 MB/s;
  • Complex recirculation set-ups;
  • More than 3 sub-arrays;
  • On-the-fly (OTF) interferometric mosaicing;
  • Complex phased array observations (e.g., pulsar and complex VLBI observing modes);
  • Low-band observations using new receivers at P-band (230-470 MHz) and 4-band (58-84 MHz)

There are two ways for individuals to take part in VLA development activities via the RSRO program.  The first is to write a science proposal explicitly requesting a RSRO capability.  The second path is to apply to come to the VLA to help with development and, if desired, apply for observing time while at the VLA.  Both options are described below.

RSRO participation via a science proposal:

A Resident Shared Risk Observing proposal is allowed an extra two pages compared with general observing proposals.  RSRO proposals should contain:

  1. A scientific and technical justification, to be peer reviewed as part of NRAO's current time allocation process, submitted through the Proposal Submission Tool.  The RSRO resources are not part of the Proposal Submission Tool, however.  Instead, the justification should include details of expected observing set-up, data rate, data volume, and post-processing requirements.
  2. The scientific and technical justification should also name the personnel who will be involved in the residency and describe how their expertise will be used to address the critical priorities of VLA development relating to their proposal.  The proposed dates of the residency must be included, so that the residency can be matched to VLA development planning.  This section will be reviewed by NRAO staff.
  3. A budget specifying the level and nature of any support requested from NRAO.  It is expected that NRAO will be able to provide accommodation in the NRAO Guest House, subject to availability.  Other support may be available separately through the NRAO Visitor's Program.  Proposals that do not require Observatory support will have a substantial advantage over those that request NRAO resources.

The acceptance of a RSRO proposal will depend on the merits of all three sections of the proposal, and will be judged in terms of the benefits to the VLA development process by NRAO staff.

One month of resident commissioning effort is required for every 20 hours of VLA time awarded to a RSRO project.  Unlike previous years, there is no minimum requirement for the amount of residency at NRAO however, the amount of time spent at NRAO to help develop the program should be realistically matched to the expected effort.  The time proposed at NRAO should be discussed with NRAO staff to determine what is reasonable.  The length of time a RSRO expert should be needed at NRAO is expected to be on the order of a few months.

The period(s) of residency may occur in advance of the observing time awarded in order to decouple essential scientific requirements (such as array configuration) from other factors which may affect when personnel are available (such as teaching schedules).  However, observers should be present for one week prior to their observations in order to become familiar with the latest developments and to set up their observations.  In the special case of Target of Opportunity proposals a VLA staff collaborator will be required for setting up observations on short timescales.

It should be noted that having a member of the NRAO-VLA staff as a collaborator on a RSRO proposal will not satisfy the residency requirement.  Graduate students may satisfy the residency requirement, provided relevant expertise is demonstrated in section (b) of the proposal.  Graduate students should be accompanied by their adviser at the start of their residency.  Resident personnel will work under NRAO management in order to optimize the overall effort.  A set of clear goals will be agreed upon in advance of the start of the residency.

The types of proposals considered under the RSRO program may include both large (>200 hours) and small (~10-200 hours) projects.  Qualified large projects proposed by consortia will be considered as long as the residency requirements are met.  A single individual may satisfy the residency requirement for several small projects.

Resident observers will also be permitted to take part in the "exploratory proposal" section of the NRAO VLA Development - Staff Observing program, in addition to the time allocated by the process described above. Thus, once a person has obtained RSRO time, they may also apply for "exploratory time" through the Director's Discretionary Time allocation process by writing a proposal request to the Assistant Director for NM Operations.

RSRO participation without a science proposal:

In some cases, an individual may want to participate in development activities without writing a science proposal.  This is especially true for individuals who want to work on the Low-band system and obtain access to the first Low-band data through exploratory time even though proposals are not being accepted for Low-band observations.

A participant may arrange to visit Socorro to contribute to development activities by submitting a proposal directly to the Assistant Director for NM Operations (nraonmad@nrao.edu) containing items (b) and (c) of the RSRO Proposal requirements described above.  If the Director approves of the request then the individual may come to Socorro to contribute to development activities.

The participant may obtain observing time either by submitting part (a) at a regular proposal deadline, or through the "exploratory proposal" section of the NRAO VLA Development - Staff Observing program while in residence (see below).  Such visits should conform to the residency requirements above.  Proposals to visit Socorro under this program may be submitted at any time.

The VLA Staff Observing Program:

The scientific staff of NRAO-NM have had an immense stake in the Expanded VLA project and in the continuing improvement of the VLA capabilities.  Observatory staff are also in the best position to test and validate enhanced or emerging capabilities of the VLA.  In order to optimize the extent to which the staff can push the instrument and certify its data products, no instrumental constraints (e.g., upon correlator capabilities) will be placed on the observing resources available to staff observers, and up to 500 hours per year will be reserved for peer-reviewed staff access to the VLA under the shared risk observing program.  Assignment of telescope time under this program will also be on a shared-risk basis in the sense that no implied commitments to complete each observing program will be made.  NRAO VLA staff who are allocated observing time under this program will also be free to collaborate on Shared Risk and RSRO projects.   However, NRAO VLA staff will not satisfy the residency requirement on RSRO proposals as stated above.

Exploratory proposals for small projects (<10 hours of VLA time) by NRAO VLA staff, or residents working on VLA development, will also be considered under this program.  Such proposals will be reviewed quickly via a process similar to that currently used for exploratory proposals.

Questions regarding the Shared Risk or RSRO programs should be directed to Debra Shepherd (dshepher@nrao.edu).