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## Geometric and Instrumental Delay in a Radio Interferometer

31 Aug 2017, 20:12 UTC
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Question: For an east-west array, in u,v, w coordinate, w=0. Does it mean that for the east-west array, there is no geometric delay from the phase reference center? And did we need to add the instrumental delay? Thanks very much. It is very confusing for me to understand the relationship between e^(-j2*pi*w) and the instrumental delay. — Shui
Answer: First of all, for an East-West array w is not necessarily equal to zero. The w-coordinate is in the direction of the object being observed. For an East-West array, when a source goes through transit the geometric delay is equal to zero. One always needs to add any instrumental delay to the total delay for an interferometer. For reference, there is a nice description of how an interferometer works in practice on the University of Virginia Astronomy 534 chapter on Interferometers.
Jeff Mangum