VLBI Field Operations - Control Files file: vlbi_experiment_files.wpd

Skd File

Complete instructions for any given VLBI experiment are contained in a global schedule (.skd) file that is prepared by the experiment's PI. A copy of the skd file is sent to or downloaded by every participating field station as well as by the correlator station where the tapes will be analyzed. Included in the skd are:

1. A table of all the scans included in the experiment. Each scan entry has a header containing the scan's assigned identification number, a data taking mode, the source name, and a nominal start time. After the header the rest of the scan entry includes a line of special instructions for each of the participating field sites. These instructions include the site name, data taking (data valid) start and stop times for the site w.r.t. the nominal start time, pass number, etc.

2. Specifications for each mode appearing in the scan table (frequency, BBC set up etc).

3. Sky position for each source name included in the scan table (RA, Dec, Epoch)

4. Data analysis instructions for the correlator station

5. Reference data for each site (latitude, longitude, etc) needed by the correlator station

Each field site runs the skd file through the program DRUDG to produce a SNAP (.snp) file and a Procedure (.prc) file. DRUDG uses data from local equipment and configuration files, so the snap file and procedure files are tailored to the field site that produced them.

SNAP File

The SNAP file is the local schedule file; it is chronological list of times, followed by the events that will take place at those times when the experiment is run. These events include: execute a given set up procedure, give the pointing computer new sky coordinates, turn on tape, turn on data valid flag, operator prompts, rewind for a few seconds and then read that data to measure the number of parity errors, etc.

Procedure File

Some or most of the setup procedures called by the SNAP file are custom made for the given experiment. These are found in the .prc file made by DRUDG from this experiment's SKD file. Other procedures are more general and are already known to the field system.

Summary File

The skd, snp, and prc files are all machine read, even if they are in ASCII text format and can be printed and read by the experimenters. But a 'for eyes only' file, the summary file, provides a written summary of the experiment.