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.     

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.     

Possible levels of reducing radio wave reflection from an aerodynamic object covered by an absorbing plasma

We estimate the possible levels of reducing backward reflection of radio waves from an aerodynamic object covered by an absorbing plasma created on the object at tropospheric flight altitudes. This effect is analyzed in terms of a model one-dimensional problem of radio wave propagation in inhomogeneous layers of absorbing plasma. 5th Central Testing Institute of the Department of Defense of the Russian Federation, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 9, pp. 893–899, September, 1999.     

应用一维变分法反演GPS掩星大气温湿廓线

GPS掩星观测的折射率是大气温度、湿度状态的函数, 应用一维变分方法 (1DVAR) 可以从折射率资料中同时反演出大气温、湿度廓线, 利用COSMIC 2011年中国区域掩星观测数据对这一方法进行了测试, 背景场采用ECMWF大气廓线, 反演结果与相匹配的探空观测有较好一致性. 重点研究了一维变分反演方法中非理想气体效应 (non-ideal effect) 对温度、湿度反演误差的影响, 不同月份的比较结果表明, 非理想气体效应对掩星反演大气廓线是一种系统性影响, 考虑这一效应可对温度反演改进0.1 K的偏差 (bias), 对比湿可改进约0.5%偏差. 掩星资料作为数值天气预报资料同化中少数无需偏差改正的卫星遥感资料, 非理想气体效应改正是无疑是非常重要的, 此外, 考虑这一效应对掩星资料的气候应用也有重要价值. 关键词： 一维变分 掩星 非理想气体效应     

Fine structure of solar radio bursts at meter wavelengths: A survey

Conclusions Our survey indicates that diverse fine structure is an important (and frequently decisive) property of many radio bursts. As far as we can judge from the available data, however, this type of structure is hardly observed in every phenomenon. One of the major tasks for future research, therefore, is to determine the specific conditions over the active regions that result in the appearance of particular types of fine structure.In particular, the solution of this problem calls for combining observations with a high degree of time and frequency resolution with instrument observations with high angular resolution, which are capable of localizing sources of fine structure within the limits of burst generation regions.Information on the specific conditions under which fine structure arises will help to formulate more definite opinions about possible generation mechanisms both of the fine structure itself and of the associated radio bursts. This information is also necessary in order to link conceptions of radio-burst fine structure with the overall development pattern of solar activity and, in particular, with the phenomena that accompany bursts as a whole.Institute of Terrestrial Magnetism, the Ionosphere, and Radio Wave Propagation, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 20, No. 9, pp. 1255–1301, September, 1977.     

Experimental determination of physical processes in space,leading to deviations of radio synchrotron radiation spectra from the power law

We present universal formulas for spectral characteristics of cosmic radio sources of synchrotron radiation upon the presence of spectral density maxima at certain frequencies (spectra with negative curvature) taking into account most typical physical processes observed in space. On the basis of long-term observations of angular radiation structure of cosmic radio sources in the decameter wavelength range by the URAN radio interferometer system, we determine most probable physical processes resulting in spectra with extremum values for several quasars, radio galaxies, and their separate components. On the basis of these data, we estimate some parameters of cosmic medium, magnetic field, and angular sizes of compact radio sources and their components. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 2, pp. 91–110, February 2008.     

Seasonal behavior of middle-latitude short-wave mesospheric radio echoes

Using the radar of the “Sura” facility, we studied the diurnal and seasonal behavior of mesospheric middle-latitude short-wave radio echoes. It was, found that the diurnal dependence of the intensity of reflected signals is mainly determined by the solar illumination of the mesosphere, i.e., by photoionization intensity. We revealed an almost permanent and season-independent presence of a thin turbulent layer at altitudes of 82 to 84 km whose radio echoes are maximal in summer and winter and much weaker in spring and fall. Sporadic summer radio echoes with increased intensity, which are observed at somewhat greater (by 2 to 4 km) altitudes, apparently correspond to the phenomenon of mesospheric summer echo (MSE) observed in the VHF range. The material of the article has been reported at the IIIrd International School on Space Plasma Physics. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebmykh Zavedenii, Radiofizika, Vol. 41, No. 10, pp. 1248–1257, October 1998.     

Dependence of radio emission from mercury on the structure and morphology of its outer layers

We present the results of a theoretical study of the dependence of radio emission from Mercury at wavelengths 0.3–76.8 cm on the structure and composition of its outer layer. Employing different models for the structure of this layer, we show that the radiative component of the heat flux strongly influences the effective temperature and its spectral characteristics. Using the two-stratum model, we demonstrate that account of morphological inhomogeneity over the depth of the outer layer is crucial for interpreting the data on radio emission from Mercury measured with high resolution over the planet’s surface. The obtained results may be useful for comparing experimental data with theory to determine the physical characteristics of the upper cover of Mercury. The results of this paper were partially reported at the XXVII Radio Astronomical Conference (St. Petersburg, November 10–14, 1997) [1]. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 3, pp. 203–214, March 1999.     

Preliminary data on decameter type IIId bursts with echo components obtained from a two-dimensional radio heliograph

We present for the first time a set of intensity-time records for one solar type IIId radio burst with an echo component obtained as a result of angular selection of the radiation observed using an UTR 2 antenna operating in the mode of a two-dimensional heliograph at f=25 MHz. It is found that in the case of such events, which occur only in the central sector of heliolongitudes |l|≤50°, the apparent pulsating source of narrow-band (∼0.1 MHz) radiation at the second harmonic (f≈2f_p) can have a complex, constantly varying angular structure. The coronal source positions determined at the time of the main peak of a two-hump burst and 6.5 s later at the time of its second, relatively low, maximum did not coincide and their divergence was ≈12′ in hour angle and ≈0′ in declination. During the first pulse (having a steep front) the source did not remain immobile and travelled for 3 s, gradually decaying, predominantly to the west at an average velocity close to the velocity of light. The amazing fact of initial nonstationarity and other properties of the pulsing type IIId source show that a fast imaginary source occurred in the solar corona at the site of short-time (< 1 s) radio wave generation, i.e., well above the normal level of plasma frequency . The background of the source was obviously an extended opaque or translucent region of disturbed plasma. Operating as a passive retranslator of signals, at the plasma levels f_p∼f/2 this strange coronal structure could prevent the radio waves, including those reflected specularly at the plasma level deep in the corona, from propagating freely. Most probably, this is exactly the reason why the decay of the echo component is slow and nonmonotonic in the case of type IIId bursts, many of which pulsate rhythmically 3 or 4 times. Radioastronomical Institute, Kharkov, Ukraine; Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 1, pp. 105–120, January, 1998.     

Observation of ultrahigh-energy cosmic rays with the ANITA balloon-borne radio interferometer

We report the observation of 16 cosmic ray events with a mean energy of 1.5 × 101? eV via radio pulses originating from the interaction of the cosmic ray air shower with the Antarctic geomagnetic field, a process known as geosynchrotron emission. We present measurements in the 300-900 MHz range, which are the first self-triggered, first ultrawide band, first far-field, and the highest energy sample of cosmic ray events collected with the radio technique. Their properties are inconsistent with current ground-based geosynchrotron models. The emission is 100% polarized in the plane perpendicular to the projected geomagnetic field. Fourteen events are seen to have a phase inversion due to reflection of the radio beam off the ice surface, and two additional events are seen directly from above the horizon. Based on a likelihood analysis, we estimate angular pointing precision of order 2° for the event arrival directions.     

Constraining fast radio burst progenitors with gravitational lensing

Fast Radio Bursts(FRBs)are new transient radio sources discovered recently.Because of the angular resolution restriction in radio surveys,no optical counter part has been identified yet so it is hard to determine the progenitor of FRBs.In this paper we propose to use radio lensing survey to constrain FRB progenitors.We show that,different types of progenitors lead to different probabilities for a FRB to be gravitationally lensed by dark matter halos in foreground galaxies,since different type progenitors result in different redshift distributions of FRBs.For example,the redshift distribution of FRBs arising from double stars shifts toward lower redshift than of the FRBs arising from single stars,because double stars and single stars have different evolution timescales.With detailed calculations,we predict that the FRB sample size for producing one lensing event varies significantly for different FRB progenitor models.We argue that this fact can be used to distinguish different FRB models and also discuss the practical possibility of using lensing observation in radio surveys to constrain FRB progenitors.     

The guyed NIRFI radio telescope

Conclusions The experiment of planning, constructing, and operating the RTVS-12 radio telescope has demonstrated that it is possible in principle to use a prestressed guyed rod spatial structure for the construction of a fully steerable reflecting antenna.One of the main advantages of this antenna over other antennas of the same size is the light weight of the dish, 1.3 tons. As far as we know, a dish with the usual girder structure weighs 2–4 times as much (unfortunately, there is little data on small-diameter dishes, and moreover, different authors mean different things by the weight of the dish).The RTVS-12 radio telescope was created as an instrument for decameter wavelengths, that is, the dish was not designed to have a high surface accuracy. In operating the antenna, however, it became clear that it could operate at shorter wavelengths.The RTVS-12 antenna was a practical test of techniques for calculating similar structures; the accuracy of force calculations for a portable guyed system was determined and the basic shortcomings and omissions were made evident. The data obtained have enabled us to begin planning a guyed radio telescope with a dish 36 m in diameter, with a better perfected structural plan for the dish and the support-rotation structure.Scientific-Research Institute of Radiophysics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 22, No. 11, pp. 1293–1300, November, 1979.     

Frequency dependence of the radio frequency collapse effect

A systematic study of the dependence of the radio frequency (rf) collapse effect on the frequency of the rf field which induces the fast relaxation of the hyperfine field was performed for Permalloy and amorphous Fe₄₅Ni₃₀Si₁₀B₁₅ alloy. The rf collapse was studied for the frequency range of 12 MHz to 64 MHz. The results show that the rf collapse appears gradually in both materials as the rf field frequency exceeds the Larmor frequency what is in agreement with the model predictions.     

Computer model of a meteor radio channel

A computer model of a meteor radio channel is presented. The model is based on the Monte-Carlo method. The possibility of effective choice of the model parameters is proved. The simulation results agree well with the experimental data obtained in meteor radio lines with lengths of 240, 700, and 1100 km.State University, Kazan. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 11, pp. 1177–1186, November, 1995.     

Utilization of photon orbital angular momentum in the low-frequency radio domain

We show numerically that vector antenna arrays can generate radio beams that exhibit spin and orbital angular momentum characteristics similar to those of helical Laguerre-Gauss laser beams in paraxial optics. For low frequencies (< or = 1 GHz), digital techniques can be used to coherently measure the instantaneous, local field vectors and to manipulate them in software. This enables new types of experiments that go beyond what is possible in optics. It allows information-rich radio astronomy and paves the way for novel wireless communication concepts.     

Regularization methods in radio interferometry

The problem of image retrieval in radio interferometry is a classical example of an ill-posed problem. In this paper, we consider a new approach to the radio-interferometric imaging based on regularization, which is computationally more flexible. A new type of a weighting function suitable for managing the interferometer antenna pattern is obtained. The regularization procedure was implemented in the VLBI-image processing software developed at the Astrospace Center of the Lebedev Physical Institute (ASC LPI). It is shown that the joint use of the developed regularization methods with traditional deconvolution algorithms such as CLEAN and self-calibration improve the quality of images of cosmic radio-emission sources. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 6, pp. 453–460, June 2007.     

Optimal space separator of signals and noise in radio communication channels. 2. Experimental studies

We present experimental results obtained for a device for signal separation with angular manipulation and separation of different types of noise in SLW-SW communication channels. We show the high efficiency of signal separation from a signal-noise mixture in almost perfect communication channels. The algorithm which we devised was tested by a real-time signal processor model under laboratory conditions. The experimental data were compared with the numerical results. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 517–529, April, 1997.     

Diagnostics of the solar corona structure by the refraction effects on radio emission

The solar disc radio brightness distribution observed at RATAN-600 can be interpreted as the angular directivity of the disk center emission at viewing anglesΘ=arcsin(R/R₀) over an angular range of R<0.9R ₀ at several wavelengths in the 2.0–32 cm region. These spectra can be treated as an emission enhancement due to refraction effects in free-free corona emission. The model simulations show good agreement with the observations and lead to estimation of the electron density N_e=1·10 ⁹ cm^?3 and emission measureEM=6·10 ²⁶ cm^?5 for the quiet Sun.     

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 thermomagnetic instability during ionospheric modification by powerful radio waves

The possibility of excitation of thermomagnetic instability in the ionospheric F-region with an external DC electric field on exposure to waves from powerful ground-based radio transmissions is discussed. The threshold and growth rate of the instability are determined. It is shown that such instability can appear in local regions with a rather high level of plasma waves and in the high-latitude ionosphere, especially for high ionospheric-plasma drift velocities.Scientific-Research Institute of Radiophysics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 5, pp. 674–679, May, 1994.