Aperture Synthesis and Interferometry

Abstract

To record the image of a sunset we point the camera toward the setting sun, and the rays diverging from the various elements of the scene fall on the lens and are focused, element by element, on the film. Some people undoubtedly conceive of a camera as a device that reaches out and captures the distant scene, and years ago it was vigorously contended that vision reached out from the eye much as a hand reaches out in a dark room to explore the surroundings. It is, of course, perfectly all right to describe photography as in the introductory sentence above, but with the caveat that the description involves information about certain entities (the source elements and the propagation medium) that are unascertainable by the camera alone. In many branches of science the output of the observing instruments is the only information—astronomy is one example, and seismic exploration of the earth’s interior is another. Both of these endeavors produce images of inaccessible regions of physical space, and they suggest another, more operational, way of describing image formation.