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VLBA System Monitoring Observations

by Tony Perreault last modified May 07, 2019 by Meri Stanley

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. For comments, please write to: analysts@nrao.edu