Chapter 5
Making Images from Interferometer Data

This chapter is devoted to the use of AIPS to make and improve images from interferometer visibility data. It begins with a brief description of the routes by which such data arrive in AIPS. The basics of weighting, gridding, and Fourier transforming the data to make the so-called “dirty” image are described, followed by a discussion of deconvolution, particularly Clean. The output of Clean is a model of the sky which, in cases of good signal-to-noise, can be fed back to improve the calibration of the interferometer data, a process called “self-calibration.” How this is done in AIPS is described. This entire process often isolates bad data samples, not previously removed from the data set. An interactive, baseline-based data editor called EDITR is described at the end of the chapter. You may find it more useful than TVFLG (O.1.6) for removing data at this stage in the processing. Task IMAGR now does “3-dimensional” imaging, SCMAP contains an editing option at each self-calibration cycle, and EDITR has replaced IBLED as the baseline-based editor of choice. A UV -plane based interactive editor called UFLAG became available in 31DEC16.

Lists of AIPS software appropriate to this chapter can be obtained at your terminal by typing ABOUT UV  C R, ABOUT CALIBRATION  C R, ABOUT EDITING  C R, and ABOUT IMAGING  C R. Relatively recent versions of these lists are also given in Chapter 13 below. Basic data calibration is discussed in Chapter 4, editing is discussed in 4.3.5 and 8.1, and imaging and self-calibration are also discussed in 8.4 for spectral-line data and in 9.7 for VLBI data.

 5.1 Preparing uv data for imaging
  5.1.1 Indexing the data — PRTTP
  5.1.2 Loading the data — FITLD and UVLOD
  5.1.3 Sorting the data — UVSRT
  5.1.4 Combining data sets for imaging — DBCON and VBGLU
 5.2 Basic image making — IMAGR
  5.2.1 Making a simple image
  5.2.2 Imaging multiple fields and image coordinates
  5.2.3 Data weighting
  5.2.4 Cell and image size, shifting
  5.2.5 Zero-spacing issues
 5.3 Deconvolving images
  5.3.1 Basic Cleaning with IMAGR
  5.3.2 Multiple fields in IMAGR
  5.3.3 Clean boxes and the TV in IMAGR
  5.3.4 Experimental variations on Clean in IMAGR
  5.3.5 Data correction options in IMAGR
  5.3.6 Manipulating Clean components
  5.3.7 Image-plane deconvolution methods
 5.4 Self-calibration
  5.4.1 Self-calibration sequence and SCMAP or SCIMG
  5.4.2 Self-calibration with CALIB
  5.4.3 Considerations in setting CALIB inputs
  5.4.4 Evaluating the quality of the imaging
  5.4.5 Experimental extension of multi-field self-calibration
 5.5 More editing of uv data
  5.5.1 General remarks on, and tools for, editing
  5.5.2 Baseline-based uv-data editing — EDITR
 5.6 Imaging with OBIT, Complex imaging
 5.7 Additional recipes