Accumulation of Fourier Component Phases during Observation of an Object with an Orbital Telescope

Kornienko, Yu. V.; Lyashenko, Ilya; Pugach, V. V.; Skuratovskiy, Sergey I.

doi:10.3103/s0884591320010031

Cited by 3 publications

(3 citation statements)

References 6 publications

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“…Some of these approximations are quite difficult to ensure, and a number of methods are being developed to reduce the impact of their violation, among themundersampling and deconvolution, isoplanatism (Schwab, 1984), spectral behavior (Taylor et al, 1999), non-coplanarity (Shopbell et al, 2005), direction-dependent calibration effects (Bhatnagar et al, 2013), etc. The difficulties of taking into account the inhomogeneities of the medium of wave propagation, primarily the non-stationary ionosphere, give rise to the socalled phase problem in low-frequency radio astronomy (Kornienko et al, 2008(Kornienko et al, , 2020. In addition, reconstruction of radio images belongs to the class of inverse problems.…”

Section: Introductionmentioning

confidence: 99%

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Direct Image Reconstruction in Multi-Element Interferometry

Lozynskyy,

Ivantyshyn,

Rusyn

2023

OAP

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The Ukrainian VLBI system of decameter radio telescopes URAN successfully solves many scientific problems, but implementing aperture synthesis technology has a number of difficulties. One of them is significant phase distortions in this range caused by an inhomogeneous propagation environment. Therefore, the task arose to develop an alternative technology with the conventional name "Interferovision", which would allow us to restore radio images with a limited number of antennas, operate with broadband signals, not require flatness of the objects scene, and have an extended field of view. A method of direct image reconstruction when observing objects in space, using a multi-element interferometer, is proposed. This method is based on a physically based principle that is similar to holography. The wave front is registered by the antennas of the interferometer, and further processing is equivalent to its playback in reverse and registration of the resulting spatial interference image. There are no special requirements for the radiation of individual points of the source, except for its delta correlation. A finite frequency band is considered, and each point can be characterized by its own spectrum, that is, its own autocorrelation function of radiation. The resolution of the direct reconstruction method depends on its width. With the quasi-monochromatic approximation, the autocorrelation functions of the radiation of all the source points degenerate into sinusoids, and the restoration of the image becomes possible only with the use of the Fourier transformation. A theoretical justification of the method for spaces of different dimensions has been obtained. Interferometric systems of the same rank with many antennas are reduced to a same canonical form with fixed number of virtual antennas placed at the origin of the coordinates and at unit distances on the coordinate axes. The ambiguity of the obtained solution is eliminated by using an additional antenna. A simulation of the proposed method of direct image reconstruction for two-dimensional space was carried out. Despite the low conditionality of the system for estimating the distance, when it increases, the angular characteristics are preserved. Therefore, the method is promising for restoring radio images of space radio sources.

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Section: Introductionmentioning

confidence: 99%

“…Another approach is based on the use of the longitudinal correlation function (Koshovy et al, 1998) followed by the Radon transform (Koshovy et al, 2002& Lozynskyy et al, 2023. Image reconstruction is carried out by inverse Radon transform based on a set of received projections for pairs of antennas.…”

Section: Introductionmentioning

confidence: 99%

Direct Image Reconstruction in Multi-Element Interferometry

Lozynskyy,

Ivantyshyn,

Rusyn

2023

OAP

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“…Some of these approximations are rather difficult to ensure, and a number of methods are being developed to reduce the impact of their violation, including undersampling and deconvolution, isoplanatism [11], spectral behavior [12], non-coplanarity [13], directiondependent calibration effects [14], etc. The difficulties of taking into account the inhomogeneities of the medium of wave propagation, primarily the non-stationary ionosphere, give rise to the so-called phase problem in low-frequency radio astronomy [15,16]. In addition, reconstruction of radio images belongs to the class of inverse incorrect problems.…”

Section: Introductionmentioning

confidence: 99%

1-D Interferometer in 3-D Space and Radon Transform

Lozynskyy,

Rusyn,

Ivantyshyn

2023

ELIT

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Observations in three-dimensional space using an interferometer generally require a corresponding rank of the base vector system of the interferometric system. The paper considers one of the ways to solve such a problem using a 1D interferometer with a moving antenna. Due to its movement, it is possible to synthesize an interferometer of a higher rank, similar to aperture synthesis. Moving the moving antenna in the plane allows formation of a 2D interferometer. The obtained analytical expressions show that such an interferometer performs the Radon transform of the angular structure of the spatial image when observing sources far beyond the size of the interferometer base. In the quasi-monochromatic approximation, a comparison is made between the van Cittert-Zernike theorem, which is widely used in such problems, and the considered transformation. It is shown that the obtained conclusions agree well with each other, while the Radon transform better meets the problem and is free from a number of limitations.

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