Spectral-line analysis of very-long-baseline interferometric data

Several topics concerning the processing and interpretation of data obtained with very-long-baseline (VLB) interferometers--i.e., tape-recorder interferometers--from spectral-line radio sources are discussed. The instrumental phase shifts are traced through the interferometer. The spectral resolution and normalization of the visiblity spectrum are discussed. Expressions for estimating fringe amplitude, and the associated signal-to-noise ratio, are derived for the case when the integration time exceeds the coherence time of the interferometer. Procedures are presented for measuring the relative spatial distribution of a widely separated collection of point sources utilizing fringe-phase data and rate of change of fringe-phase data.