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Paper: Very Long Baseline Interferometry
Volume: 180, Synthesis Imaging in Radio Astronomy II
Page: 433
Authors: Walker, R. C.
Abstract: Very Long Baseline Interferometry is the branch of radio interferometry that uses antennas that have no direct link for data and/or clocks. The baseline lengths are limited only by the size of the Earth, and not even that for space VLBI. The resolution is very high --- of order a milliarcsecond. This allows imaging of galactic objects with sizes of about an astronomical unit and of extragalactic objects, even at high redshift, with sizes of about a parsec. The wide separation of antennas makes stabilization of phases difficult because of the need for a high accuracy model and because of the very different atmospheres over each antenna. But great progress has been made in the last few years with the advent of the VLBA. For many VLBI observations now, the data reduction techniques and sensitivity are similar to those of connected interferometers. In this chapter, the process of making a VLBI observation is described with emphasis on those areas that differ from connected element interferometer practice. There is special emphasis on techniques for groups, along with unaffiliated antennas, can observe together in the AIPS approach because of the author's experience. But for some convergence of the self-calibration procedure that the author has
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