C.4 VLBA Utilities

Note that there are simple VLBA procedures (“front ends” to standard tasks) that will take the user all the way from data loading up to and including fringe-fitting. These are tremendous labor-savers for those working with reasonably straightforward data sets. For spectral line, use the procedures to calibrate a lower spectral resolution version of the spectral line data and copy the final calibration to the line set. To access the utilities, type RUN VLBAUTIL from inside . The procedures that we will use in this appendix are:

• VLBALOAD: loads VLBA data with simplified inputs
• VLBASUMM: makes summary listings of your data set
• VLBAFIX: Fixes VLBA data
• VLBATECR: automatically downloads and applies ionospheric corrections
• VLBAEOPS: automatically downloads and applies corrections to the Earth Orientation Parameters used by the correlator
• VLBACCOR: determines amplitude corrections caused by errors in sampler thresholds
• VLBAPANG: determines phase corrections for parallactic angles
• VLBAPCOR: determines instrumental phase corrections using pulse cals
• VLBAMPCL: determines instrumental phase corrections using FRING
• VLBACPOL: calibrates cross polarization delays
• VLBABPSS: does bandpass calibration
• VLBAAMP: does adjustment due to normalization errors and a-priori amplitude calibration
• VLBAFRNG: does global fringe fit using FRING
• VLBAFRGP: does global fringe fit for phase referenced experiments using FRING
• VLBASNPL: plots the SN or CL tables versus time
• VLBACRPL: plots the cross-correlation spectrum

There are two additional procedures that can make life easier, called ANTNUM and SCANTIME. ANTNUM will return the antenna number of the antenna corresponding to a certain character string. For example, in many data sets, typing REFANT = ANTNUM (’BR’) will be the equivalent of typing REFANT = 1. SCANTIME will return the time range of a given scan number, for use in various programs. Typing TIMERANG = SCANTIME(4) will fill the eight-element array TIMERANG with the start and stop times of the 4^th scan of a given data set.

Note that all of the VLBAUTIL procedures have HELP files with good discussions about when to use the simple procedures and when to use the tasks directly. Also, note that the procedures do not include data editing, which should be performed at appropriate points in the calibration process. You only need to RUN VLBAUTIL once to access all of the procedures. If you run it again for any reason, it is a good idea to type COMPRESS immediately afterward to avoid overflowing śymbol memory.