Facilities > VLBA > VLBA Shared Risk Observing

VLBA Shared Risk Observing

by Jonathan Romney last modified Jul 02, 2019 by Mark Claussen


The VLBA Shared Risk Observing (SRO) program allows observers access to capabilities that are essentially commissioned, but are not well tested. In semester 2020A  shared risk observing on the VLBA includes:

  1. The use of a single VLA antenna as a VLBI station (Y1), and
  2. Copying baseband data to user-provided disk packs (baseband copy).

If proposers are in doubt as to whether their proposed setups are Shared Risk or Resident Shared Risk are encouraged to get in touch with NRAO staff (e.g. by using the NRAO helpdesk) well before the proposal deadline.  We emphasize the "shared risk" nature of the SRO program. Since observers will be attempting to use capabilities that are not well-tested, NRAO can make no guarantee of the success of any observations made under this program, and no additional commitment is made beyond granting the hours actually assigned by the peer review process.

Using a single antenna as a VLBI station - Y1

 A single VLA antenna can be used as a VLBI station with the VLBA.  This allows short baselines from nearby VLBA stations, e.g. the Pt or La VLBA station.   Short baselines, on the order of a few tens of km, allow better imaging of larger scale structures.  The VLA WIDAR correlator allows the use of subarrays, with the Y1 antenna as a single-antenna subarray to provide matched frequency setups to the VLBA.  The VLA currently has both Mark5c and Mark6 disk recorders, with Mark5c recording as the production mode, and the Mark 6 undergoing tests.  The use of Y1 as a VLBI station is part of the VLBA Shared Risk program, and must be selected as part of a Resource in a VLBA proposal using the NRAO Proposal Submission Tool (PST).

Baseband data copy

The raw data recorded on the station recorders can be copied to user-supplied media for correlation at a different location that has the capability of  reading VLBA baseband data (in VDIF format).   For a successful proposal requesting this VLBA Shared Risk capability, the following items should be addressed in the proposal:

  • If correlation is needed to be performed elsewhere; e.g. a higher time resolution than can be provided by the VLBA DiFX correlator
  • The use of baseband copy should be fully justified in the proposal, either in the technical justification, or the science justification of the proposal
  • The acceptance and consideration of the request of baseband copy is subject to VLBA resources available
  • Proposers are expected to provide their own media storage, which is compatible with the copy mechanism

The use of baseband copying may be requested by selecting the "Baseband Copy" checkbox under "Special Features" in the VLBA Resource in the PST.

Questions or request for clarifications on baseband copy to other media should be sent to the NRAO helpdesk.