Digital receivers for low-frequency radio telescopes UTR-2, URAN, GURT

This paper describes digital radio astronomical receivers used for decameter and meter wavelength observations. This paper describes digital radio astronomical receivers used for decameter and meter wavelength observations. Since 1998, digital receivers performing on-the-fly dynamic spectrum calculations or waveform data recording without data loss have been used at the UTR-2 radio telescope, the URAN VLBI system, and the GURT new generation radio telescope. Here we detail these receivers developed for operation in the strong interference environment that prevails in the decameter wavelength range. Data collected with these receivers allowed us to discover numerous radio astronomical objects and phenomena at low frequencies, a summary of which is also presented.Comment: 24 pages, 15 figure

A Method of Air Object Recognition Based on the Normalized Contour Descriptors and A Complex-valued Neural Network

This paper reports a study into the methods for recognizing the type of an air object on a digital image acquired from an air situation video monitoring system. A method has been proposed that is based on the application of a specific neural network, which solves the problem of categorizing multidimensional complex vectors of objects' features based on complex calculations. In this case, a feature vector for recognizing the type of an air object is built on the basis of a Fourier transform for the sequence of coordinates of its two-dimensional contour. A technique has been proposed to train a neural network to recognize the type of an air object based on three image classes corresponding to three projections. This makes it easier to solve the classification problem owing to a more compact arrangement of the multidimensional feature vectors. The architecture of an air situation video monitoring system has been suggested, which includes an image preprocessing module and a module of a complex-valued neural network. Pre-processing makes it possible to identify an object's contour and build a sequence of normalized descriptors, which are partially independent of the spatial position of the object and the contour processing technique. Existing methods of air object recognition require significant computational resources and do not take into consideration the specificity of recognizing objects with three degrees of freedom or do not account for the complex nature of the numerical representation of a contour. This study has shown that the reported results make it easier to train a neural network and reduce the hardware requirements in order to solve the task of air situation video monitoring. The proposed solution leads to increased mobility and extends the scope of application of such systems, including individual device

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New Antennas and Methods for the Low Frequency Stellar and Planetary Radio Astronomy. Planetary Radio Emissions| PLANETARY RADIO EMISSIONS VII 7|

According to the special Program of the National Academy of Sciences of Ukraine, creation of the new giant Ukrainian radio telescope (GURT) was started a few years ago on the UTR-2 radio telescope observatory. The main goal is to reach maximum band at the lowest frequencies (10-70 MHz), effective area (step-by-step up to 100,000 sq.m), and high interference immunity for resolving many astrophysical tasks when the sensitivity is less limited by the confusion effects. These tasks include stellar radio astronomy (the Sun, solar wind, flare stars, pulsars, transients) and planetary one (Jupiter, planetary lightnings, Earth ionosphere, the Moon, exoplanets). This array should be complementary to the LOFAR, E-LOFAR systems. The first stages of the GURT (6 x 25 cross-dipole active elements) and broad-band digital registration of the impulsive and sporadic events were tested in comparison with the existing largest decameter array UTR-2

Astrophysical Studies with Small Low-Frequency Radio Telescopes of New Generation

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State-of-the-art of low frequency radio astronomy, relevant antenna systems and international cooperation in Ukraine

International audienceThe low frequency radio astronomy (decameter-meter range, frequencies of 10-300 MHz) currently demonstrates rapid progress all over the world. New generations of large antennas-LOFAR, LWA, MWA and others – have been created in many countries. At the same time Ukrainian radio astronomical systems UTR-2 and URAN still remain the largest and most informative ones at the lowest frequency range available for the ground-based radio astronomy (below 33 MHz), especially after their radical modernization during the most recent years. A great number of top priority results have been obtained on the basis of these radio telescopes. The results prove a high significance of the low frequency radio astronomy for astrophysics. Substantial part of these results have been obtained in the course of many year cooperation between Ukraine on one side and France, Austria, Germany and other countries on the other. Creation of new low frequency instruments GURT (Ukraine) and LSS/NenuFAR (France) for the wide frequency range of 10-80 MHz opens up new possibilities for research and fruitful cooperation

Multi-antenna observations in the low-frequency radio astronomy of solar system objects and related topics studies

International audienceRapid progress currently takes place in the field of low-frequency radio astronomy in the meter-decameter-hectometer range of wavelengths. It is caused by a radical modernization of the existing radio telescopes, creation of a new generation of instruments, space-borne observations, and by the development of research on all classes of astrophysical objects, including the Solar System. On the other hand, a range of difficulties specific to low-frequency radio astronomy is known, which are caused by technical, methodological, and physical limitations. An effective strategy for overcoming these difficulties is based on synchronous observations using several radio telescopes separated by distances from a few to several thousand kilometers. This provides an opportunity to reduce and identify radio interference and the influence of the propagation media, to increase the sensitivity and resolution, and to solve many problems with higher efficiency. In recent years such simultaneous observations were carried out for the Sun, Jupiter, Saturn, interplanetary medium, pulsars, exoplanets, and transients using the radio telescopes UTR-2, URAN, GURT, NDA, NenuFAR, LOFAR and other. Parallel observations with the space missions WIND, STEREO, Cassini and Juno also facilitate improvement of the quality and reliability of low-frequency radio astronomical experiments

The modern radio astronomy network in Ukraine: UTR-2, URAN and GURT

International audienceThe current status of the large decameter radio telescope UTR-2 (Ukrainian T-shaped Radio telescope) together with its VLBI system called URAN is described in detail. By modernization of these instruments through implementation of novel versatile analog and digital devices as well as new observation techniques, the observational capabilities of UTR-2 have been substantially enhanced. The total effective area of UTR-2 and URAN arrays reaches 200 000 m2, with 24 MHz observational bandwidth (within the 8-32 MHz frequency range), spectral and temporal resolutions down to 4 kHz and 0.5 msec in dynamic spectrum mode or virtually unlimited in waveform mode. Depending on the spectral and temporal resolutions and confusion effects, the sensitivity of UTR-2 varies from a few Jy to a few mJy, and the angular resolution ranges from ~ 30 arcminutes (with a single antenna array) to a few arcseconds (in VLBI mode). In the framework of national and international research projects conducted in recent years, many new results on Solar system objects, the Galaxy and Metagalaxy have been obtained. In order to extend the observation frequency range to 8-80 MHz and enlarge the dimensions of the UTR-2 array, a new instrument - GURT (Giant Ukrainian Radio Telescope) - is now under construction. The radio telescope systems described herein can be used in synergy with other existing low-frequency arrays such as LOFAR, LWA, NenuFAR, as well as provide ground-based support for space-based instruments