Proceedings PaperCoherent integration of fringe visibility employing probabilistic determinations of atmospheric delay
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Coherent integration of fringe visibility in an optical stellar interferometer yields much higher signal-to-noise ratios is shorter integration periods for dim objects. Furthermore coherent integration, if performed simultaneously over multiple spectral channels, can yield direct determination of the phase of the visibility function, a quantity that is lost in incoherent integration. To perform coherent integration it is necessary to estimate the random atmospheric delay to well within a wavelength. That determination can be used either to compensate for the delay in hardware, or as a 'phase reference' for integration of fringe visibility with the correction applied in software. This paper primarily addresses the latter method, presenting algorithms for the proper estimation of optical correlation given the interaction between the statistics of the incoming light and the hardware. Of particular importance is the effect of error in the estimation of the atmospheric delay used as a reference phase. The author's previously published method for estimation of the atmospheric delay achieves well modeled error levels. In the case of very weak signal, even 'ambiguous' determinations of atmospheric delay can be used for phase referencing. The delay estimator may employ the same raw data used for estimation of fringe visibility.