Chapter 5
MAKING IMAGES FROM INTERFEROMETER DATA

This chapter is devoted to the use of  to make and improve images from interferometer visibility data. It begins with a brief description of the routes by which such data arrive in . 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  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 (§4.4.3) for removing data at this stage in the processing. This chapter has been revised for the 31DEC07 release of  and some portions of it do not apply to really old releases. In particular, 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. Tasks MX, HORUS, et al., which are now obsolete, are no longer described.

Lists of  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 §4.4 and §8.1, and imaging and self-calibration are also discussed in §8.4 for spectral-line data and in §9.6 for VLBI data.