Aperture synthesis

Aperture synthesis is a type of interferometry that mixes signals from a collection of instruments to produce measurements having the same angular resolution as an instrument the size of the entire collection. At each separation and orientation, the lobe-pattern of the interferometer produces an output which is one component of the Fourier transform of the spatial distribution of the brightness of the observed object. In order to produce a high quality image, a large number of different separations between different telescopes are required (the projected separation between any two telescopes as seen from the radio source is called a baseline) - as many different baselines as possible are required in order to get good quality results. Most aperture synthesis interferometers use the rotation of the Earth to increase the number of different baselines included in an observation (see diagram on right). Taking data at different times provides measurements with different telescope separations and angles without the need for buying additional telescopes or moving the telescopes manually (the rotation of the Earth moves the telescopes for you!). Some instruments use artificial rotation of the interferometer array instead of Earth rotation, such as in Aperture Masking Interferometry.

External Links

• Further details of aperture synthesis in radio astronomy
• Cambridge Optical Aperture Synthesis Telescope

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