VLBA

Additional VLBI Opportunities

The VLBA is a stand-alone VLBI array that is useful for addressing many scientific questions. However, in some cases, more sensitive telescopes, longer baselines, or additional high-frequency antennas are necessary to reach science goals. Some additional opportunities are described in the following links:

• VLBI at the VLA
• European VLBI Network (EVN)
• Global cm (EVN+VLBA) should propose through the EVN proposal tool, Northstar
• Global mm-VLBI

The VLBA Shared Risk Observing (SRO) program allows observers access to capabilities that are essentially commissioned, but are not well tested. Note that if a shared risk project fails, it may not be re-observed. In semester 2025A  shared risk observing on the VLBA includes:

1. Recording wide-band VLA visibilities in parallel with phased VLA (Y27) VLBI, 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.

For more information on General Observing (GO), Shared Risk Observing (SRO), and Resident Shared Risk Observing (RSRO), please see the VLBA Observational Status Summary Offered Capabilities section.

Recording wide-band VLA visibilities in parallel with Y27 VLBI

In addition to recording VLA phased array (Y27) data on the Mark 6 unit for VLBI purposes, this mode will deliver wider bandwidth data through WIDAR for the VLA itself. This would be useful to optimize the sensitivity of the VLA observations as a secondary (VLA only) science product. Currently, this only supports standard VLA 8-bit continuum modes with a 2-GHz bandwidth. To request VLA wide-band data for a project, specify your needs in the final box of the Technical Justification ("Note any other technical considerations..."). 

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.

Data points are accumulated from weekly pointing tests. Some of the plots crop outlier points to increase readability.

Welcome to the VLBA System Monitoring Observations webpage. The main purpose of this page is to direct observers to VLBA monitoring observations that may aid them in determining the general quality of data from their own observations and to help diagnose possible problems seen in their datasets.

VLBA operations is now releasing a subset of observed projects without intense scrutiny of the data after correlation by AOC in-house personnel. Weekly monitoring observations will be used to determine the general health of the VLBA observing system (from antenna through correlation). Problems, adverse conditions, or malfunctions detected in these monitoring sessions will be listed in text files along with useful plots in the web accessible directories located at . The type of plots that can be found are the same as those generated for individual science projects: tape recording and playback weights, autocorrelation bandpass and amplitudes, cross-correlation bandpass phases and amplitudes, and baseline rate; delay; phase; and amplitude versus time.

If you are interested in the report or plots from a monitoring session or sessions, proceed to the VLBA System Monitoring Calendar page for the year of interest by selecting a link below. This will display the observation date of each session which is linked to that specific project directory on the vlbiobs system. The project directory will contain an ASCII text file named monitor.txt which summarizes the results of the observation and lists problems that could affect data. Also listed are one or two subdirectories which contain the monitoring (or 'sniffer') plots. Each subdirectory is named using the two alphabetic character code for the reference station used to generate the plots (i.e. PT for the VLBA Pie Town antenna or LA for the VLBA Los Alamos antenna).

Also available are text files containing all monitoring observation reports listed in chronological order for a given year. Links to these files are listed below.

VLBA System Monitoring Calendars are available for the following years

Interpretation of the Monitoring Reports and Plots:

1. The monitoring report summarizes the overall health of the VLBA system and states any problems detected in the final correlated data which may affect science observations that were observed around the time of the monitoring experiment. After consulting the report, observers should check their own data to confirm if a problem affects their observation.
2. Mark5 playback weights versus time plots have been generated for the entire time range of these monitoring observations. However, poor playback and weights from the correlation of a monitoring experiment may have little relevance to the observer's science project. Observers are asked to check their own weights plots in the vlbiobs project directory of their own observation to determine the quality of tape recording and correlation playback. Refer to your PI letter Email with the description of where these plots are located and what information they contain.
3. Autocorrelation bandpass plots are generated for all antennas at each front-end receiver frequency band, excluding 3mm. Certain types of RFI, receiver, LO system and base-band converter concerns can be diagnosed from these types of plots.
4. Cross-correlation bandpass plots as well as delay, rate, phase, and amplitude versus time plots are generated for the entire observation. These plots are useful in assessing problems with correlation, clock delays, station positions, polarization, etc.
5. Observers should note that RFI (Radio Frequency Interference) seen in the same frequency band in the monitoring observation as their observation may not occur in the observers' datasets and vice versa since RFI is very dependent upon the actual frequencies observed which may differ considerably. Observers should carefully check the autocorrelation plots in the vlbiobs project directory of their own project to determine the extent that RFI may have affected the data.

This page is maintained by the VLBA Data Analyst group. Send questions and comments to the NRAO helpdesk.

Technical Justification for Proposals

Since the actual Technical Justification depends strongly on the science, the frequencies and correlator setup, etc. it is difficult to give general guidelines.  Instead, we present the example below, in this for case multi-epoch astrometry.  Click to enlarge.