Data Processing

The primary data reduction package for the VLA is the CASA (Common Astronomy Software Applications) package, which is also used for ALMA.

The Astronomical Image Processing System (AIPS) can be used to reduce VLA observations. AIPS is currently required for the reduction and analysis of phased-array VLA observations for VLBI.NRAO will continue to support AIPS for the foreseeable future, at least until VLBI functionality have been incorporated into CASA.

The following pages are designed to help VLA observers understand, and process, their data. For instructions on obtaining VLA data, see the archive web page. If you are new to radio astronomy (and interferometry in general), you might consider reading Chapter 7 of Astronomy Methods (Bradt, 2004) as well as the first several lectures in Synthesis Imaging in Radio Astronomy II (ASP Conference Series Vol. 180). You may also find useful information in the lectures from the 15th Synthesis Imaging Workshop.

Analysis Packages

 The two main analysis packages used for the processing of VLA data are AIPS and CASA.

VLA Calibration Pipeline

 The VLA calibration pipeline performs basic flagging and calibration using CASA. It runs automatically at the completion of all science scheduling blocks (SBs).

VLA Imaging Pipeline

 The VLA imaging pipelineto make VLA continuum images using the aggregate bandwidth available in given data set.

Science Ready Data Products

 The goal of the SRDP Initiative is to improve the user experience for VLA data by providing users with science quality data as well as providing tools for data processing and discovery through an updated archive interface.

Computing Resources

 Describes acceptable use of NRAO computing facilities for the purpose of calibration and imaging VLA and VLBA observations at the New Mexico Array Science Center (NMASC).

Baseline Corrections

 NRAO monitors the positions of the VLA antennas on a regular basis -- roughly monthly, and more often during reconfigurations. This involves observing a number of calibrators spread around the sky, solving for the antenna-based gains, and from their behavior deriving the three-dimensional positions of those antennas (see, e.g., chapter 12 of Thompsan, Moran, and Swenson 1991, Interferometry and Synthesis in Radio Astronomy, for a fuller discussion). These corrections (generally less than a centimeter) are then inserted into the correlator model in the on-line system.

Post-Processing Issues

 Issues that have impact on VLA data/image quality.

Connect with NRAO

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