Interferometric method for image formation: investigation of potentialities by means of computer simulation

Abstract

Shortening of the wavelength in radioastronomy eventually should result in application of image formation methods characteristic for optics. It is justified and even it is desirable already in mm and the more so in submm a range. Thus, as always, one of the main tasks is the increase of resolution of astronomical instruments. As it is known, the key resolution limit of an astronomical instrument is determined by diffraction of the incoming wave on the instrument aperture. However, at observation from the Earth surface in a short-wave side of a wave band, it is seldom possible to achieve this limit because of the phase contortions arising at propagation of a wave in the Earth atmosphere from the fluctuations of the refraction index. There is a series of ideas how to form an astronomical image decreasing or excluding influence of phase distortions during observation One of such methods is the interferometric imaging method. The point of this method is that an image is not formed directly in the telescope focal plane, as it is done at the traditional method. Instead of this the interferometer entrance aperture is divided into sub-apertures. Image reconstruction from an interferogram obtained requires removing unknown phase distortions from several independent measurements of the coherence function by different pairs of sub-apertures and find true values of the Fourier-components of the object brightness. Thereto it is necessary to solve the algebraic system of equations connecting the results of measurements of the coherence function phases with their true values and phase distortions in the atmosphere. This idea is verified well using a computer model of the optical system, when the brightness distribution over the object is known exactly and may be compared with the image reconstructed.