1.1 Overview

SCHED is a program for scheduling Very Long Baseline Interferometer (VLBI) Observations. It can be used to schedule any observations on antennas that use the VLBA real time control software and to schedule Mark IV/VLBA(4)/S2/Mark5 observations on any stations that can read VEX format schedules. SCHED is the program used to schedule essentially all non-geodetic VLBA projects and has been adopted by the European VLBI Network (EVN) as the standard scheduling program for the EVN. SCHED is also a useful tool for planning observations, both at proposal writing time and before making detailed schedules. The plotting capabilities are especially useful for this.

To use SCHED, one normally creates an input file, using any text editor, that describes the schedule. Then SCHED is run on that file. A number of examples are distributed with SCHED. The usual and recommended way to make a schedule is to copy one of the examples and modify it according to your specific needs. When developing a schedule, it is likely that SCHED will be run several times before everything is to the scheduler’s satisfaction. The various output files, especially the summary file and the optional plots, provide a lot of information about the schedule that can be used to help the user with optimization.

SCHED gets a lot of information, including station locations and equipment, source positions, and frequency setups, from a number of catalogs. Most catalogs can be imbedded in the schedule, but it is much more common to use the standard ones provided with the SCHED distribution. An effort has been made to put as much information as possible in the catalogs so that the user only need provide very generic information specific to the particular project. But if the user wants to do something special, it is possible to specify the parameters of an observation in great detail. Documenting all these capabilities partially explains the large size of this manual, most of which is not needed by the average user.

SCHED writes several different types of output files, some of which are useful for the scheduler and some of which are meant for the computers at the antennas. An outline of the files used by SCHED can be found in the section on files. The summary file is the most important one for the user. It gives the details of the equipment setups at each station and a summary of various items about the individual scans.

The beginning user might start by looking at one or more of the example files to get a sense of what they look like. Then read some of the sections that cover important details, without which it might be difficult to understand what is going on. The section on KEYIN Free Format Input covers the capabilities and limitations of the parser used to read all input files. The section on Inpuut and Output files gives an overview of the information that SCHED requires. The Running SCHED section has instructions on how to start the program. And the Examples section contains 2 examples of SCHED input files and quick descriptions of, and links to, most of the rest provided with the distribution.

After reading the sections recommended above, it would probably be best to use one of the examples to experiment with the program. The examples are complete, working files. In fact, they are all used regularly to test SCHED modifications. They will work as is, and it can be modified to try other features. The easiest way to make a schedule for your project will usually be to select the example that is closest to what you are trying to do and modify it to your needs. It is not strictly necessary to read the rest of the manual. It can be treated as a reference to help answer questions.

The files needed to run SCHED are in various subdirectories under the base directory used for the SCHED installation. That base directory, on unix systems, should be assigned by you or your system administrators to the environment variable SCHED. The key subdirectories are examples, setups, catalogs, doc, src, and bin and can be referred to, on unix systems, using paths such as $SCHED/catalogs. For most the contents are obvious from the names. src contains the code and bin contains the executables, perhaps in architecture dependent subdirectories. The user should work in a private directory and only refer to files in the SCHED standard areas, not modify them. All SCHED output files are written in the current working directory.

There is a lot of information about SCHED and about the process of scheduling VLBI observations in the descriptions of the input parameters and of the parameters for the setup files. There are detailed discussions of some specific areas of concern in the Scheduling Tips Section . This section will be expanded significantly in the future. All of these sections are worth reading through on some slow day for those serious about scheduling.

VLBI projects can also be produced using the NASA Goddard program SKED and VLBA control files can be produced using DRUDG. That is the standard path used by the geodesy community, but is rare among astronomers.

SCHED may be obtained by anonymous ftp from ftp.aoc.nrao.edu under directory pub/sched. For more information, see the section on Installing SCHED. Users are encouraged to obtained the current release of SCHED before attempting to make schedules. The program is continually evolving to support new features and to make it harder to write schedules that won’t work. It is in your own best interests to have the current version. For most users, installing a new version should involve little more than copying and unpacking the tar files and copying the executable for their type of machine.

A note on notation: the names of computer programs will be given in SMALL CAPS font, the names of files will appear in slant font, and the names of SCHED and setup file parameters will appear in typewriter font. Some parameters may be abbreviated; where both compulsory and optional characters are displayed, the compulsory ones will be shown in UPPER-CASE TYPEWRITER font and the optional ones shown in lower-case typewriter font.