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F.P. Schloerb, R.S. Millan-Gabet (U. Massachusetts), W.A. Traub (Harvard-Smithsonian CfA)
The measurement of visibilities with a long baseline interferometer is complicated by atmospheric propagation effects. We present a technique for estimating and calibrating visibility measurements that we have developed for the Infrared-Optical Telescope Array (IOTA). The technique makes use of the fact that the IOTA makes many hundreds of individual measurements of fringe visibility on a source within a few minutes time. The large number of measurements allows the distribution of the visibilities to be well determined and used in the estimation procedure. We have found that simple estimators, such as the mean or median of the distribution, yield results that vary significantly under different seeing conditions. However, this problem is substantially reduced when the observed visibility distibution is fit to a physical model that includes known atmospheric propagation effects. In this paper, we present the details of the physical model and show how its use in the visibility estimation procedure improves the calibration and consistency of the interferometric data.
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