Atmospheric phase fluctuations due to nonuniformly distributed water vapor in the lower troposphere present a challenging problem to millimeter wavelength interferometers. Measurements of the variation in atmospheric radiometer noise and a representative atmospheric velocity lead to reasonable estimates of the atmospheric phase stability as a function of baseline length and timescale. Such estimates are useful for site selection, estimating the image quality during different atmospheric conditions, estimating the useful amount of observing time at high frequencies, and evaluating observing and calibration strategies.
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