Institute of Astronomy
Kharkiv National University

NATIONAL PROPERTY OF UKRAINE

Coherent-optical image processor
of Institute of Astronomy, Kharkiv V.N. Karazin National University

History

The Research Institute of Astronomy of V. N. Karazin Kharkiv National University was founded in 2002 on the basis of the University Astronomical Observatory, one of the oldest observatories in Ukraine. Many famous scientists worked at the Observatory. Prof. L. O. Struve was a founder of Kharkiv astrometry, astrophysicist academician V. G. Fessenkov started planetary studies at the Observatory. American astronomer Otto Struve started his scientific career in Kharkiv University; later he headed a number of American astronomical institutions and was a President of the International Astronomical Union. In 1918 academician N. P. Barabashov began systematic optical studies of the Moon. The main results of Kharkiv astronomers were obtained in the field of planetary science.

Recent planetary studies in the Institute use photometric and polarimetric observations of asteroids, comets, Jupiter, and the Moon. Kharkiv astronomers analyze results of space missions to the Moon (Clementine, Lunar Prospector), Mars (Mars Global Surveyor), Venus (Pioneer-Venus, Magellan, Venera 13–16), and Phobos (Phobos-2 mission). Since the end of the 60's several successive efforts were undertaken to develop image-processing facility and algorithms for high-resolution imaging with ground-based optical telescopes. The unique equipment "Coherent-optical image processor" was designed and manufactured in 1973 under the direction of prof. V. N. Dudinov for fundamental investigations in the field of optics, radiophysics, astrophysics, and defense. The instrument was settled in out-of-town Observational Station of Astronomical Institute that is located at 75 km to the south-east from Kharkiv (the equipment needs to be unaffected by any seismic factors).

Physical principles of processor operation and its optical scheme

The Coherent-Otical Image Processor (COIP) is an analogue "computer" which allows amplitude and phase-amplitude filtration of images. It incudes high-quality lens that privides Fourier transformation of transparencies that are illuminated by a beam of parallel coherent light. In our instrument transparencies (original images) are placed inside of special lens that are cuvetes filled up with an immersion liquid to reduce of phase noise of the transparencies. These lens-cuvetes are Fourier transformation components of the image processor.

Coherent-optical image processor provides of:

• modeling and investigation of any range complexity optical or radioastronomical systems;
• modeling and investigation of coherent light propagation through stochastically phase- heterogeneous medium;
• receiving and investigation of statistical characteristics (power spectra, correlation functions) of complicated two-dimensions images with high information composition;
• investigation of interference and diffraction phenomena, coherent properties of electromagnetic radiation;
• holographic investigations;
• laboratory practical work on physical optics and adjacent fields for students.

COIP was use for the next real tasks:

• defense activity;
• increase of spatial resolution of Earth-based and spaceborn images;
• discerning artificial space objects;
• analyzing sea surface parameters to reveal submarine tracks.

Methods of specle-interferometry allow us to determine angle distances between components of double stars. The main point of the methods is that the period of interferograms is inversely proportional to the angular distance between the stars. Results of such a method as applied to the task are shown below.

The "Coherent-optical processor" is applied in astrophysical researches.

COIP has been successfully used to improve the images obtained with cameras of the first spaceborn missions to the Moon and planets.

An important problem in nowadays astronomy is the revealing and searching of planetary systems near others stars in our Galaxy. Many different methods are using to solve this problem. One of the methods is searching the autocorrelation functions and Fourier spectra of eclipsed stars.

COIP in mode of laser extra-small phase-angle photometer

A lot of information about chemical composition and mineralogy, structure and physical properties of celestial bodies, natural or artificial surfaces can be acquired by remote spectrophotometrical methods. Analysis of phase curves of scattering surfaces, especially in range of very small phase angles ("opposition effect" at 5° - 0°), is one of it.

To provide laboratory photometry under phase-angles lower 0.01° we have developed an extra-small phases photometer that allows us to investigate the opposition effect in mentioned phase angles range. This photometer has been developed on base of the "Coherent-optical image processor". The smallest accessible phase angle is 0.008°; the angular resolution of the photometer is 0.005°; the angular diameter of light spot on target as it looks from the photometer position is about 0.11°.

Recent observations of Kuiper belt objects revealed noticeable spike in backscattering. It somewhat contradicts to low albedo of their surfaces, since low albedo is not in accordance with the coherent backscatter enhancement theory of the opposition effect. An important point is that the observations can be made only in the range of very small phase angles. To check and investigate the phenomenon, laboratory measurements of phase curves of surfaces with well-controlled properties at the same phase angles are very useful. We have made these measurements with the image processor.