Post-Processing Software

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AIPS, NRAO's Astronomical Image Processing System, is a set of programs for the analysis of continuum and line observations, and is widely used with VLBA and VLBI data.  These programs are available for a wide range of computer operating systems, including various flavors of Linux and the Mac-OS/X operating system.   Extensive online internal documentation can be accessed within AIPS.  An entire chapter in the AIPS Cookbook (NRAO staff, 2007) provides useful "how-to" guidance those reducing VLBI data, including discussion of VLBA calibration transfer, space VLBI, polarimetry, and phase referencing.   Appendix C of the AIPS Cookbook provides a step-by-step guide to calibrating many types of VLBA data sets in AIPS, employing simple VLBA utilities, including calibration modifications for VLBA+VLA datasets.

A new ''frozen" version of AIPS is produced each year, and a newer version is updated and made available throughout the calendar year. Observers are encouraged to use a very recent version of AIPS, in order to keep up with ongoing  developments in VLBA instrumentation.

AIPS home page:


CASA (Common Astronomy Software Applications) is the new data reduction package that will be used for the EVLA and ALMA. It does not yet offer an end-to-end reduction path for VLBA data.  However, CASA does contain imaging and calibration tools that may be of use for VLBI data.

CASA home page:

3. Difmap

Difmap (Shepherd 1997) provides editing, imaging, self-calibration, and pipelining capabilities in an interactive package.  It was developed as part of the Caltech VLBI Analysis Programs and remains widely used, although development has been frozen and continued support is limited primarily to assistance in installation.

Difmap download site:  Contact: M.C. Shepherd,