Method of cosmic radiation recording in spectral lines

We propose a method for recording of energy parameters of cosmic radio emission in spectral lines, differing in the principle of amplitude calibration of the reception-measurement channel. This method does not require the use of additional channels of signal-power measurement and reduces the source observation time required for extraction of a signal from noise and its recording. Radio emission is recorded using a standard high-sensitivity receiver of the RT-32 radio telescope and a digital spectrum analyzer based on the fast Fourier transform. We consider two variants of the recording system: a variant with off-shelf general-purpose spectrum analyzers (e.g., NI-5620), which use PC processors, and a variant with high-speed specialized analyzers based on programmable logical devices. The system with an XC4VLX25 integrated-circuit analyzer is operated in a frequency band of up to 32 MHz and has a minimum response time, which makes it possible to minimize the source observation time. The spectrum recording system developed at the Institute of Applied Astronomy of the Russian Academy of Sciences and “Radioelectronic Technological Equipment Ltd” and supported by a project of the Russian Science Agency was put into service in the “Svetloe” radioastronomical observatory in 2006. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 9, pp. 777–788, September 2008.     

A 151 MHZ radioastronomical antenna of wave channel elements

We describe a simple, inexpensive multibeam receiving antenna array with wavelength λ=2 m for radioastronomical studies of the solar wind by interplanetary scintillation observations of a large number of weak space radio sources. Radioastronomical Observatory of the Astrocosmic Center of the Lebedev Physical Institute, Pushchino, Moscow region, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 7, pp. 824–840, July, 1998.     

On the features of decameter radio astronomy

We consider some effects of the VHF radio wave propagation in randomly irregular plasma near the Earth. Applications of these effects to main problems of decameter radio astronomy are discussed. In particular, we show that significant measurement errors of about tens to hundreds of percent for the intensity of the VHF radio emission from an extra-terrestrial source may occur due to scattering and focusing/defocusing of the radiation in the ionosphere if VHF radio astronomical facilities operate at middle latitudes. We find that the angular resolution of discrete radio sources observed using radio interferometry and the well-known scintillation methods cannot be better than about a degree due to the effect of the developed ionospheric turbulence. We propose a modified scintillation method based on the spectral analysis of radio emission from discrete sources, which allows the useful high-frequency signal corresponding to diffraction of VHF emission at weak inhomogeneities of interplanetary plasma to be separated against strong, relatively low-frequency fluctuations of the received radiation due to the effect of the developed turbulent structure of the ionosphere. We show that such a method allows the angular resolution of extra-terrestrial radio sources to be improved up to arcsecond level. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 2, pp. 95–105, February 2000.     

A differential method of maximum entropy

We consider a differential method of maximum entropy that is based on the linearity of Fourier transform and involves reconstruction of images from the differences of the visibility function. The efficiency of the method is demonstrated with respect to the recovery of source images with bright components against the background of a sufficiently weak extended base. The simulation results are given along with the maps of an extragalactic radio source 0059+581, which were obtained using the standard and differential methods of maximum entropy for three observation dates and show that the principle of differential mapping allows us to increase considerably the dynamic interval of images. Institute of Applied Astronomy, Russian Academy of Sciences, St. Petersburg, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 8, pp. 991–998, August, 1998.     

Measurement of antenna parameters by signals from space satellites of the GLONASS and Navstar navigation systems

We present the results of experiments on measuring the antenna pattern and alignment of the RT-14 and RT-15 radio telescopes located in the radioastronomy observatories of the Radiophysical Research Institute of Nizhny Novgorod by signals from space satellites of the GLONASS and Navstar navigation systems. The efficiency of using signals of the navigation satellites to measure a number of parameters of the antenna systems is analyzed.     

Modifications of the reddi method and their limiting resolution of high-power random sources

In the limit of large signal-to-noise ratio, we compare the resolutions of the Reddi method and its modification based on exact knowledge of the central position between the resolved sources with both traditional and arbitrary specification of the prediction element (at the ends of the antenna array). The sources were assumed to be independent Gaussian and equivalent, and the equality of the mean objective function at the points of actual location of sources to its value at the midpoint between the sources was used as the resolution criterion. Academician Mints Radio Engineering Institute, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 8, pp. 1035–1041, August, 1997.     

On the scintillations of radiation from an extended source in a randomly inhomogeneous medium

Using the method of refractive scattering of radio waves (RSRW), we solve the problem of space correlation of scintillations of radiation from an extended source in a randomly inhomogeneous medium. General expressions are obtained for the index and radius of the space correlation of fluctuations of intensity of radiation from a source with finite angular dimensions as it propagates though a multilayered medium with refractive index fluctuations. The RSRW method is similar to the diffraction calculation of space correlation of scintillations of an extended source in a thick layer with inhomogeneities. We note that under certain conditions an increase in the number of inhomogeneous layers on the radio wave propagation path leads to a pronounced decrease in the scintillation index and an increase in the space correlation of fluctuations of intensity of received radiation from an extended source. The results obtained have a simple geometric-optical interpretation. We indicate a specific feature in determining the angular dimensions of extended radio sources using the known method of scintillations. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 5, pp. 586–593, May, 1997.     

On the problem of nonlinear distortions of the maximum-entropy method

We consider the problem of nonlinear distortions resulting from noise in the input data in the reconstruction of images from incomplete Fourier spectra using nonlinear information-theoretic methods, in particular, the maximum-entropy method. Comparison of traditional and generalized maximum-entropy methods shows that generalized methods, which operate in the space of complex functions, provide the best agreement of the solution with the data and, therefore, a minimal level of nonlinear distortions. Recommendations for processing of real nonnegative images of incoherent radio sources are given.Institute of Applied Astronomy, Russian Academy of Sciencies St. Petersburg. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 12, pp. 1267–1277, December, 1995.     

VLBI studies of the solar-wind plasma irregularities at 18 and 92 CM wavelengths in 1994–1996

We discuss the capabilities of VLBI studies of irregularities of the solar-wind plasma using multi-element radio interferometric facilities. We analyze the data obtained during international VLBI experiments at decimeter wavelengths (92 and 18 cm) in 1994–1996 and supposed that the irregularities have a “stream” structure. The “streams” are strongly elongated in the solar-wind direction (longitudinal size of about a few hundred thousand kilometers) and have the transverse size of about 0.5–2.0 thousand kilometers. The irregularities inside a single “stream” are almost isotropic. We discuss the restrictions imposed on operation of decimeter VLBI systems due to effects of the interplanetary medium. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 3, pp. 197–206, March, 2000     

Background fluctuations in the GPS-microlab-1 ionospheric radio sounding experiment

We analyze the spectra of the phase and amplitude fluctuations of radio signals recorded in the course of four ionospheric radio-sounding sessions at altitudes from 70 to 120 km. Our study is aimed at determining the sources of these fluctuations. Comparing the statistical properties of fluctuations measured at two wavelengths with theoretical calculations, we conclude that only the low-frequency part of background fluctuations is of ionospheric origin, while the high-frequency fluctuations are caused by noise of the measuring system. The amplitude fluctuations are more informative in the high-frequency region, since they are mainly due to ionospheric irregularities. We discuss the possibility of separation of the components of amplitude fluctuations caused by ionospheric irregularities and the irregularities of the neutral atmosphere in the case of sounding at the altitudes at which those components have comparable values. It is shown that this problem cannot be solved by dispersion and extrapolation methods, which are used for separation of the regular ionospheric and atmospheric components of the amplitude and phase variations of radio signals. A. N. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 6, pp. 511–523, June 1999.     

Study of an angular radio axis displacement model for 64-meter TNA 1500 radio telescopes (russia)

A model taking into account the technical characteristics of the mechanisms, constructions, and devices of angular control has been developed to standardize systematic angular errors in the guidance system of 64-meter TNA 1500 radio telescopes. To define the structure of the experimental spectrum of systematic errors obtained from the data on the complex radiometric angular standardization of the radio axis, we used an approximation algorithm based on the least squares criterion for the set of functions which follows from the proposed model of corrections. Experimental Design Bureau, Power Engineering Institute, Moscow; Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 11, pp. 1370–1377, November, 1997.     

Correlation theory of the thermal regime and thermal radiation of a medium with random boundary conditions

We present the results of a spectral approach to the previously developed statistical theory of temperature distribution and thermal radio emission of a medium (half-space), which is based on results of simultaneous solution of equations of thermal radio emission transfer and thermal diffusivity. We obtained relationships expressing the covariance functions of the temperature profile and the brightness temperature of radiation in terms of statistical parameters of the temperature at the half-space boundary, which is considered to be a random stationary function of time. The possibility of using the theory for the actual atmosphere is studied. The predicted phenomenon of time shift of the correlation function maximum is observed. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 5, pp. 598–615, May, 1997.     

Detection of a sulfur dioxide radio line ν∼131 GHz in the lower troposphere

We present the results of detection of the sulfur dioxide radio line ν∼131 GHz of anthropogenic origin in the lower troposphere emission. The methods and results of spectral radiometric studies of SO₂ content near its sources are described. Institute for Space Research, Moscow; Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 6, pp. 704–712, June, 1997.     

Development of a Radioastronomical Correlation Method for Measuring Mirror-Antenna Parameters

We consider the techniques and instrumentation developed at the Radiophysical Research Institute (NIRFI) for measuring mirror-antenna parameters using signals from extraterrestrial radio sources and geostationary satellites. The results of measuring the radiation patterns of several large-scale fully-rotatory radio telescopes in a wide dynamic range and of retrieving the amplitude and phase distributions on their apertures are presented.     

Design concepts of the holographic subsurface radar

We discuss general concepts of design and signal-processing algorithms of the holographic subsurface radar. We consider a model example of the holographic image of a discrete point scatterer. An estimate of the scattered-signal level in the problem of subsurface radio sounding is given. Institute for Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Moscow region, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 3, pp. 224–233, March, 2000.     

Study of long-wave radio signal disturbances due to lightning-induced energetic electron precipitation

Observing long-wave radio signals at short distances simultaneously with the broadband reception of VLF radiations, we obtained an abrupt (by more than 10%) amplitude variation of signals from the Moscow long-wave transmitter which can be identified as the reflection of long-wave signals from lightning-induced energetic electron precipitation regions in the ionosphere. Some amplitude variation events were accompanied by single-hop whistlers which arrived from the southern hemisphere and multihop whistlers originating from the northern hemisphere. Physical and Engineering Institute, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 472–478, April, 1997.     

Model of interaction between decameter-decimenter radio waves and a strongly inhomogeneous mid-latitude ionosphere

A model of decameter-decimeter radio wave propagation in a strongly inhomogeneous mid-latitude ionosphere is constructed using a modified method of radio wave refractive scattering. The model establishes the relationship between the basic statistical radio wave characteristics and the turbulence parameters of the upper ionosphere. Different aspects of the theory of radio wave refractive scattering are considered in application to the study of amplitude and phase fluctuations of decameter-decimeter radio waves propagating in a three-dimensional randomly inhomogeneous ionosphere with an arbitrary electron density distribution. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 11, pp. 1323–1341, November, 1997.     

Global magnetospheric perturbations stimulated by the plasma wave discharge in the lower ionosphere

In this paper we discuss a new method of controlled stimulation of global perturbations and the diagnostics of plasma physical processes in the ionosphere and the magnetosphere of the Earth. The method was realized with a series of rocket experiments by means of excitation of the radio frequency plasma wave discharge in the near field of the dipole antenna [1–4]. We focus considerable attention on the results obtained in these experiments testifying to the wide choice and diversity of potentialities of this new method.Radiophysical Research Institute. Nizhny Novgorod, Russia. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 6, pp. 799–806, June, 1994.     

Modeling VHF emissivity of snow cover with account of its stratigraphy

In this paper, we discuss a model of emissivity of snow cover taking into account its structure. We assume that upward and downward radiation inside a snow layer are diffuse and apply the two-flux theory of Kubelka and Munk. Snow cover is modelled by a medium comprising discrete scatterers. In the case of dry snow, the scatterers are ice grains. Wet snow is modelled by a mixture of ice grains (with or without water envelopes) and water drops. We assume that the scatterers are spherical particles that have lognormal distribution over size. The brightness temperature of radio emission from snow cover on the soil is calculated using the data of glaciological measurements of physical parameters and microstructure of snow. Results of calculations are compared to measurements of the brightness temperature of radio emission from various types of snow covers. Space Research Institute of Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 9, pp. 845–857, August 1999.