1.3 SCHED Input and Output Files

SCHED takes input from several types of files in addition to any interactive input. All of these files can be separate, as long as SCHED can find them, or most of them can be imbedded in the main input file. The former is more convenient. But, when the input file is to be sent somewhere else to be run again, it may be safer to imbed the catalog information in the main file. All input to SCHED is in the keyin free format section. This is the same format as is used by all Caltech VLBI package programs. The input file types are:

Main Schedule Input File:
This is the file that contains the details of the particular project. It can have the most of the other files imbedded in it. This file must be created by the user. This file should be given a name like bv016.key for project BV016. See the /schedb examples for numerous samples.
Source Catalog:
These files contain the information about the sources, especially names, positions, and, for line sources, velocities. There are standard source catalogs, although the user may need to add non-standard sources. Source catalog entries can be included in the Main Schedule Input File. There are two standard source catalogs which are $SCHED/catalogs/sources.gsfc, and $SCHED/catalogs/sources.petrov, which contains sources respectively from from the Goddard geodesy group and from Leonid Petrov. The links above are actually to symbolic links to the latest catalog from each source as of the time of the SCHED release. These catalogs contain thousands of sources (near 10,000 in Petrov’s case), so the old catalog that contained a few sources from elsewhere has been abandoned. Two external catalogs can be specified if one wishes, for example, to use the standard one for calibrators and another for multiple phase centers.

Please note that this source catalog, along with the locations catalog, is updated approximately annually. It cannot be relied upon to maintain constant positions for a multi-year project. If you need constant positions, include your own set in your schedule. Otherwise, include a step in processing that accounts for changes in the assumed calibrator position. Note that the Earth orientation and station locations actually change with time (plate tectonics etc) so exact repeats of the observing geometry are not possible.

Station Catalog:
This file contains information about the antennas including names, positions, slew limits, horizons etc. There is a standard station catalog that should suffice for nearly all users. If not, entries can be included in the Main Schedule Input File. Station positions may stored separately in the Location Catalog. The standard station catalog is $SCHED/catalogs/stations_RDBE.dat. The old version for use with the legacy VLBA systems is still $SCHED/catalogs/stations.dat. By the next SCHED release, it is likely that stations.dat will be the RDBE version and the legacy version will be renamed or removed.
Location Catalog:
This file contains station locations. The standard version reflects the locations and velocities used on the VLBA correlator. It is documented along with the Station Catalog because they are tightly coupled. The Locations Catalog is optional since it is not needed if the station locations are specified in the Station Catalog. It exists separately for ease of maintenance. The standard location catalog is $SCHED/catalogs/locations.dat.
Setup Files:
These files contain the details required to configure the hardware at the stations. Different projects using the same hardware configuration can use the same setup files. There are many standard setup files are located in $SCHED/setups.
Frequency Catalog:
This file contains information about valid frequency setups at the stations. The RF ranges that can be covered and the local oscillator and polarization of each IF are given. SCHED can use this information to provide good defaults for many parameters in the setup files. The standard file should be used. Any non-standard information can be in the setup files. This file cannot be imbedded in the main input file. The standard frequency catalog, for use with the RDBE systems, is $SCHED/catalogs/freq_RDBE.dat. The legacy version is still available. It is $SCHED/catalogs/freq.dat The main difference is that the VLBA IFs are assumed to be between 512 and 1024 MHz in the RDBE version, not 500 and 1000 MHz as in the legacy version. By the next SCHED release, the RDBE version will likely become $SCHED/catalogs/freq.dat and the legacy version will be renamed or removed.
Tape Initialization File:
This file tells SCHED the properties of the tape systems at the stations and where to start on each tape. Since tapes are no longer in use, this file is mostly obsolete. However it can be used to specify use of a recording system at a station that is different from what is given as the default in the station catalog. This is generally only useful during periods when stations are transitioning between different recording systems. Note that many old files, often used as templates, contain tape initialization sections. These should be removed.
Reference Pointing Control File:
SCHED can insert scans for reference pointing at high frequencies on the VLBA and VLA. This file contains information needed to control that function. It will only be of interest for observations above 15 GHz on the VLA and at 86 GHz on the VLBA. The standard reference pointing control file is at $SCHED/catalogs/peak.cmd There is a special version related to reference pointing when using the new wideband (RDBE/MARK5C) system on the VLBA. It is $SCHED/catalogs/peak_RDBE.cmd.
Spectral Line Rest Frequencies:
SCHED can adjust the observing frequency to remove the Doppler shifts due to the motions of the Earth around the Sun and to the Sun with respect to a desired reference frame. To do this, SCHED needs to know the rest frequency of the line being observed. This is given in a lineinit section imbedded either in the main file or in the reference pointing control file. There is a file, $SCHED/catalogs/linefreqs.dat, distributed with SCHED, that gives the rest frequencies for many of the maser lines commonly observed with VLBI.
Ephemeris file:
SCHED can be used to schedule observations of planets. To do so, it obtains positions from a JPL ephemeris file. Mostly this is used for single-dish calibration observations.
Satellite file:
SCHED can also be used to schedule observations of satellites. To do so, it obtains orbital elements from the SATFILE or TLEFILE which are specified in the SATINIT section. This is used for holography and for spacecraft navigation projects. Satellite tracking is discussed in the Satellite tracking section

SCHED processes the input files and creates several output files. Most follow a naming convention that starts with the project code (bv016 will be used in the examples here) followed by a file type indicator, then a period, then a two letter station code (pt for Pie Town in the examples below). The experiment code is read by SCHED in the EXPCODE parameter in the main schedule input. The station code comes from the station catalog and a list if given in Appendix A.1. The output files are:

Summary File:
This file gives a rather extensive summary of the setups and observations. This is the most useful output file for the user as it shows how SCHED has interpreted the input commands. The file will be called, for example, bv016.sum. The items displayed for each scan can be controlled with the parameter SUMITEM.
This file reflects most of what you see on the screen when SCHED is running, plus may contain additional messages that help debug problems should they occur.
Operator Schedule Files:
These files, of which there is one per antenna, give much more information about the schedule than can be included in the summary file and are useful when that level of detail is needed. They were originally meant for the use of operators of manually controlled antennas, but now most antennas are computer controlled and these files are more useful for the scheduler. The files are named, for example, bv016sch.pt.
VLBA type Antenna Control Files (crd files):
These files provide the legacy on-line control systems of the type found at VLBA antennas with the information they need to control the observations. There is one file per antenna that uses a VLBA control computer for either full control of the station or for control of just the data acquisition system (data recorders, baseband converters etc.). The files are named, for example, bv016crd.pt. Note that the VLBA antennas currently are in transition with some items controlled by the legacy system and some by the new control system which is commanded using the VEX file.
VEX file:
This is the main output file needed by the stations for antenna and recording system control and by the correlators to process observations. It is now used by most VLBI systems around the world, not just the Goddard “Field System”. For the VLBA, it is used to control the RDBE, MARK5C, and some antenna data path switches. The legacy system, commanded by the crd files described above, still controls the antenna pointing among various functions. Both are needed. A single VEX file describes the observations for all antennas.
V2D file:
This is a template correlator setup file for the (VLBA) DiFX correlator. Information that needs to be modified from what is in the VEX file can be specified by the analysts in this file. It is also the path to transmit information about multiple phase centers per pointing to the correlator.
Flag file:
SCHED writes a file with the .flag extension that can be helpful in data processing. It contains flag entries, in the format appropriate for the AIPS task UVFLG, that cover the times when data are being recorded, but the antenna is expected to be slewing. For the VLBA, the monitor flags would usually take care of such times, but for other types of stations, such information is not always available from the logs.
Preempt file:
Starting in Oct. 2011, the VLBA will be providing observations of up to 1.5 hours on the Pie Town to Mauna Kea baseline to the USNO for EOP determination. This is in return for financial support for operations. These observations will preempt the scheduled project on the two stations. There is some flexibility to choose the exact time of the preemption so the user has been given some ability to guide the choice. Important scans can be protected using the PREEMPT parameter. Information in the preempt file, which is also in the summary file, is used by operations when picking the time for the EOP observations.
Sched can make plots of u-v coverage and of various combinations of azimuth, elevation, paralactic angle, hour angle, UT, and GST against each other. Plots can be made of the time antennas are up. Plots can be made of beams. The plot capability can be used to plot the distribution of your sources, and of the all sources in the catalog, on the sky. This is useful for looking for calibrators. In advanced modes, stations can be moved around to explore UV coverages in array configuration design projects. Also quality factors can be calculated and plotted with contours over a map of the stations. There is interactive control over the plotting, the only interactive part of SCHED. Much of this capability is mainly useful in experiment planning.
DiFX configuration file:
When making jobs for the DiFX correlator, especially as used for the VLBA, a .v2d file is used to give information not readily deduced from the .vex file. SCHED now writes a template for that file. That file is also be used to pass lists of phase centers when utilizing the DiFX multiple phase center capability.
Optimized Schedule:
When one of SCHED’s optimization modes is turned on, or geodetic segments are requested, the program writes out a file, such as bv016.sch containing the basic scan inputs for a new main schedule file. If desired, the user can use this to construct, and perhaps modify, a new optimized main schedule input. This used to be the way all optimized schedules were constructed, but now that SCHED fully processes an optimized schedule, it is rarely used or needed. The newer use is to make it easy to reproduce geodetic segments when something else is changed that would otherwise change the results of the optimization.
If the user specifies the parameter FREQLIST, SCHED will read the frequency catalog and make a table of all known setups which can be used to make observations in the specified frequency range. Then SCHED will quit without doing further processing. This is useful for planning and for information while making setup files.