Ground-based microwave thermal sounding of the atmosphere

We apply the tensor transfer equation for downward radio emission in a weakly anisotropic medium and a generalized analysis of the generation conditions for such radiation to develope a unified approach to the solution of the problem on reconstruction of the atmospheric temperature prifile over a wide altitude range (from theoustasche layer to the mesosphere) using ground-based measurements of thermal radio emission. Radio emission in the oxygen spin—rotational band centered at the wavelength 5 mm was measured with radiometer equipment of various spectral resolutions. The capabilities of the remote sounding are illustrated by the results of the temperature profile reconstruction in theoustasche layer and troposphere using the radiometric measurements of the atmospheric radio emission, as well as by the results of numerical simulations of the radiometric experiment for the upper layers of the atmosphere. Trends in development of ground-based remote sounding of the temperature are discussed. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 1, pp. 45–59, January, 1999.     

Modelling of HF wave propagation in the vicinity of quasicritical rays in the disturbed ionosphere

The results of experimental studies of the fine structure of a signal in the vicinity of the maximum observed frequency (MOF) on the Khabarovsk—Nizhny Novgorod path of oblique chirp sounding (OCS) are presented. Additional tracks were observed in the region between the high-angle and low-angle rays during magneto-ionospheric disturbances. Under strong disturbances the ionograms were of a spreading type in the vicinity of the MOF. The observed effect was modelled in the presence of travelling ionospheric disturbances (TID) with different parameters. It is shown that the stratification of the high-angle ray into several additional tracks is a maximum for TID with vertical scales km whose wave fronts make angles about 0–10° with the horizontal line. The possibilities of using the Pedersen mode as a probing wave for diagnostics of the fine structure of the ionosphere in the vicinity of the F-layer maximum are discussed. Radiophysical Research Institute, Nizhny Novgorod; State Technical University of Ioshkar-Ola, Mari Republic; Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Moscow region, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 1, pp. 3–12, January, 1998.     

Sounding of an artificially perturbed ionosphere by means of an ionosonde/position finder with chirp modulation of the signal

We describe the operation of an ionosonde/position finder with chirp modulation of the signal. The first results of measuring the characteristics of short-wave radio signals scattered by artificial small-scale inhomogeneities, which were obtained by means of an ionosonde/position finder on the IZMIRAN—“SURA”—Rostov-on-Don path are presented. It was found that under certain ionospheric conditions, the angular and frequency selection of the scattered signals take place, in which case the signals are observed simultaneously in several frequency intervals (mainly, in three, namely, 6–9.5 MHz, 10–12 MHz, and 15–18 MHz) with different angles of incidence of radio waves in the vertical plane. In this case, the incidence angles were 20◦–35◦, 18◦–32◦, and 10◦–20◦ from the horizon for the first, second, and third frequency interval, respectively. Ionograms of oblique sounding were modeled allowing for the scattering of radio waves by artificial small-scale inhomogeneities. It is shown that at frequencies from 10 to 12 MHz, aspect conditions are fulfilled for the signals ducting along the high-angle beam (Pedersen mode). At frequencies 15–18 MHz (higher than the maximum observable frequency of the forward signal on the path IZMIRAN—Rostov-on-Don), aspect scattering conditions are fulfilled for the signals incident on a scattering area in the ascending part of the trajectory. At low frequencies 6–9.5 MHz (below the maximum observed frequency of the forward signal on the IZMIRAN—Rostov-on-Don path), the observable additional signals are caused by the scattering of radio waves by artificial inhomogeneities with subsequent relfection of the scattered signal from the Earth on the “SURA”—Rostov-on-Don path. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 4, pp. 267–278, April 2009.     

Detection of magneto-gravity waves in the ionosphere by analysis of the maximum observable frequencies on oblique-sounding paths

The existence of magneto-gravity waves stipulated by the substorm activity can lead to the occurrence of traveling ionospheric disturbances, whose velocity exceeds the sound speed. For detection of magneto-gravity waves, we used experimental data on propagation of decameter radio waves on the midlatitude and subauroral oblique sounding paths Inskip–Rostov-on-Don, Cyprus–Rostovon-Don, Irkutsk–Rostov-on-Don, and Norilsk–Rostov-on-Don in December 2006 and March 2007 under conditions of weak geomagnetic disturbance. Time delays between the AE indices of polar electrojets and the maximum observable frequencies for the considered paths were established by calculation of linear correlations. These delays correspond to the times required for transport of gravity disturbances from the auroral region to the reflection points of radio waves on respective paths. Among the obtained time shifts, we mention the 5–10-min ones which correspond to increased velocity of the disturbances compared with the usual velocities of acoustic-gravity waves for the paths under study. Such cases can be related to the transport of magneto-gravity waves. Study of the spectral composition of the AE-index disturbances and recorded maximum observable frequencies shows consistency of their spectral features in the cases of increased correlation for small time delays. It is also found that the spectral features of the AE-index disturbances coincide with the spectral features of the disturbances of the horizontal component of the geomagnetic field on ground-based magnetic stations. According to calculated dispersion curves, the frequencies of magneto-gravity waves were estimated, and they turned out to be equal to ω ≈ (1–2) ・ 10⁻⁴ Hz.     

Ultralong-range sounding of the ionospheric HF channel using an ionosonde/direction finder with chirp modulation of the signal

We present the results of experimental studies of propagation of short radio waves on a long transequatorial path of Laverton (Australia) — Rostov-on-Don, which were obtained with the help of an ionosonde/direction finder with chirp modulation of the signal. It is shown that conditions for propagation of anomalous signals by means of sideband reflection of radio waves from the Himalayan Hills and the Plateau of Iran and also due to scattering of radio waves from the high-latitude ionosphere of the northern hemisphere are realized on the given path. The propagation of radio waves is modeled with allowance for their scattering by anisotropic magnetic field-aligned irregularities of a high-latitude ionosphere, which are located on the northern wall of the main ionospheric trough of the F layer. It is shown that the results of the experiment agree well with the calculated data.     

Reflection of the dynamics of interplanetary space parameters in the maximum observable frequencies on different ionospheric oblique-sounding paths

We study the correlation between variations in the solar–geophysical parameters and variations in the maximum observable frequencies (MOF) on several ionospheric short-wave oblique-sounding paths. The basic interplanetary space parameters, whose variations have the greatest impact on the MOF variations on specified paths, are determined. Variations in the B_x and B_z components of the interplanetary magnetic field (IMF) affect the MOFs on the Norilsk—Rostov-on-Don subauroral path. At mid-latitudes, the influence of the IMF components B_x, B_y, and B_z is significant on the Inskip—Rostov-on-Don and Irkutsk—Rostov-on-Don paths. On the Cyprus—Rostov-on-Don low-latitude path, the modulus of the IMF has the most pronounced effect. The density and velocity of solar wind manifest themselves in MOF variations on all paths. The technique of MOF retrieval by a neural network on the Cyprus—Rostov-on-Don and Irkutsk—Rostov-on-Don paths using the MOF data of the Inskip—Rostov-on-Don path is developed with allowance for the influence of the interplanetary space parameters. The retrieval efficiency of this technique is no less than 80%.     

Spatio-temporal correlation of the maximum observable frequency on midlatitude radio lines

We present the results of studying the spatial and temporal correlation of the maximum observable frequency on two midlatitude paths, Inskip (England)–Rostov-on-Don and Cyprus–Rostov-on-Don. Dynamics of variation in the maximum observable frequency on these paths as a function of the time of the day and geophysical conditions is explored. The presence of a high spatial correlation (up to 93.5%) between the studied maximum observable frequencies allowed the values of the maximum observable frequency on the Cyprus–Rostov-on-Don path to be retrieved from the data on the Inskip–Rostov-on-Don path by the method of artificial neural networks with a training efficiency of up to 97%. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 1, pp. 28–35, January 2009.     

Features of limb sounding of minor atmospheric constitutents at various microwave lines

We analyze the characteristics of radio emission from the middle atmosphere during limb sounding of minor gas constituents with rotational transitions of the molecules located in the atmospheric transparency windows 105–118 GHz and 180–210 GHz. Optimal frequencies and height ranges for the sounding of minor gases are found by numerical modeling for typical values of the receiver bandwidth. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 3, pp. 235–239, March 1999.     

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.     

Behavior characteristics of the index of middle-latitude F-spread

We present the results of analysis of data on ionospheric vertical sounding in Zimenki (Nizhny Novgorod) over the period from 1964 to 1992. The January ionograms are used for constructing the plots of daily indices of F-spread for an ionospheric layer. The dependence of the average monthly (January) index of F-spread on the solar activity is obtained. The index of F-spread is found to grow with time. The technogenic nature of this increase is assumed. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 3, pp. 322–327, March, 1997.     

Analysis of appearance of moving ionospheric disturbances of the “sickle” type at middle latitudes

We present the results of analysis of the data of vertical ionospheric sounding at the Zimenki test site (Nizhny Novgorod). The January and July ionograms are used to plot the dependences of the number of “sickle” type disturbances on the time of the day for the period from 1996 to 1992. A comparison with the scattering in an ionospheric F-layer for the same period is performed. A trend in the time series of the phenomenon observed is recorded. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 12, pp. 1455–1462, December, 1997.     

Calculation of optimal operating frequencies of a communication radio line according to oblique ionosphere sounding

A hardware-software complex for real-time automatic determination of the optimal operating frequencies of a communication radio line according to oblique chirp ionosphere sounding is created. Path tests of the chirp complex on midlatitude radio lines are performed. Bit error probability and the reliability of HF communication for narrow-band and broadband communication systems are estimated from the results of oblique chirp sounding. It is shown that the quality of a communication channel greatly depends on the ratio of the regular and fluctuation components of a signal, as well as on the magnetic activity level. The created chirp complex can be used as a part of the ionospheric-wave and frequency-control service for dynamic management of the radio-line frequency resource in the interests of efficient operation of different-purpose radioelectronic systems. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 1, pp. 10–21, January 2008.     

Oblique Sounding and Modeling of the Ionospheric HF Channel

We present the results of experimental studies of the distance-frequency and amplitude-frequency characteristics of the ionospheric HF channel on mid-latitude paths of oblique chirp sounding. It is shown that the maximum observed frequencies (MOFs) are subject to short-period variations with the quasi-periods from 30 min to 2 h.The amplitude of the MOF variations reaches 2 MHz and can increase up to 5–8 MHz on the Cyprus—Rostov-on-Don one-hop path in the sunrise-sunset time. It is established that the MOF fluctuations are accompanied by pronounced “cusp” features occurring in the upper rays and moving with time to the region of shorter delays, i.e., from lower to higher frequencies. The amplitude-frequency characteristics of individual propagation modes undergo deep fluctuations (up to 20–30 dB)whose quasi-period and depth depend on the frequency. It is shown that the appearance of fluctuations is caused by interference of the unresolved rays within the limits of one propagation mode. Based on the modeling, it is shown that “cusps” in oblique-sounding ionograms are due to the influence of traveling ionospheric disturbances (TIDs). The TID parameters are estimated. It is shown that conditions of the formation of “ cusps” in the distance-frequency characteristics depend on the TID amplitude, the wavelength of the disturbance wave, and the direction of its phase front with respect to the propagation path. The effect of quasi-regular frequency modulation of the Pedersen mode with a period of 250–300 kHz on the Cyprus-Rostov-on-Don chirp-sounding path is found. Altitude stratification of the ionosphere near the F-layer maximum, which is responsible for the focusing and defocusing of the Pedersen mode, is estimated. It is established that the stratification scale amounts to approximately 200–250 m. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 6, pp.455–471, June 2005.     

Laboratory spectroscope based on a multichannel radiometer

The parameters of a microwave spectrometer with simultaneous spectrum analysis (i.e., a spectroscope) based on a multichannel radiometer are studied both theoretically and experimentally. It is shown that in the operating mode with a noise sounding signal having a temperature exceeding the receiver noise temperature the limiting sensitivity of the spectroscope to the optical thickness of gas in the cell is restricted by \gg{inmin} ⋍1/Q, where Q is the radiometric gain of the system. The spectroscope sensitivity can be increased by two orders of magnitude in the millimeter wave range by using a receiver with extremely low noise temperature and a strongly cooled radiator. Sensitivity measurements of a 3 mm spectroscope in the OCS line J=7→8 (at frequency ∼97 GHz) give the value ∼ 3·10⁻⁵ cm⁻¹ for a cell of length 1 m and time constant 15 sec, which is comparable with the technical sensitivity limitof scanning spectrometers in the millimeter wave range. The possibilities of improving the spectroscope parameters are discussed. Lobachevsky State University, Nizhny Novgorod; Institute for Physics of Microstructures of the Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 7, pp. 904–912, July, 1998.     

Oblique chirp sounding of the modified ionosphere. Experiment and simulation

We present the results of experimental studies of the influence of artificial ionospheric disturbances on HF signals used for oblique sounding of the disturbed volume. The measurements have been performed by a chirp ionosonde over the path Yoshkar-Ola-“Sura”-niznhy Novgorod with length 234 km. We found the 2F2 mode to disappear (attenuation up to 20 dB) when the ionosphere is influenced by a vertical powerful radiation in the ordinary mode with long (15 min each) heating and pause intervals. Modeling of the observed effect was carried out. The calculations agree well with experimental data if the traveling ionospheric disturbances (TID) with vertical and horizontal scales l_z∼20 km and l_x∼50 km, respectively, and the relative disturbance of the electron density δN∼0.2–0.3 are amplified (generated) during the ionosphere heating. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 4, pp. 303–313, April 1999.     

Variations in the ionospheric wave perturbation spectrum during periodic heating of the plasma by high-power high-frequency radio waves

We present the results of spectral analysis of temporal variations in the Doppler frequency shift of the ionosphere-reflected signals from a high-frequency vertical ionospheric sounding radar located near the city of Kharkov in the days of exposure of the ionospheric plasma to the high-power radio emission of the Sura facility (Nizhny Novgorod) and in the reference day in the absence of such an exposure. It was established that the spectral characteristics of quasiperiodic variations in the Doppler frequency shift in the range of periods 10–60 min in the days of work of the facility and in the reference day differed significantly. This is considered as evidence in favor of the generation (amplification) of acoustic–gravity waves propagating at the ionospheric altitudes by high-power periodic high-frequency radiation of the Sura facility.     

Some results of synchronous experimental study of artificial F-spread at radiophysical test sites in nizhny novgorod province

We show some results of experiments on synchronous sounding of the ionosphere by short-wave signals at the Radiophysical Research Institute’s test site in Zimenki and Vasil’sursk, Nizhniy Novgorod province, during ionospheric modification by high-power short radiowaves from transmitters of the “Sura” facility in Vasil’sursk. In the course of experiments we proved directly the decisive role of large-scale inhomogeneities of the ionospheric plasma with dimensions of from several kilometers to several dozens of kilometers in the formation of artificial F- spread. The small-scale inhomogeneities with dimensions smaller than 1 km, which are localized in a relatively thin layer near the reflection level of a high-power short radiowave, emerged only at sounding waves, propagating (reflected) in the immediate vicinity of the center of the heating region. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 6, pp. 688–692, June, 1997.     

Gamma-ray spectral features of neutron stars originating from photon splitting in a strong magnetic field

The spectral evolution of the soft (≲1 MeV) gamma-ray radiation of neutron stars in a strong magnetic field (B ≳ 6·10¹² G) is analyzed. It is shown that the radiation transfer equation for the photon splitting cascade has a one-parameter set of self-similar solutions whose integral expansion is an efficient method for study of the general solution. An arbitrary initial spectrum converges quickly to a self-similar solution provided that most of the radiation energy is concentrated in the hard spectral range. We consider the possible observational consequences of the photon splitting, including the polarization and softening of the output spectrum as well as the occurrence of a spectral break and condensation of all hard-energy radiation near that break. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, radiofizika, Vol. 40, Nos. 1–2, pp. 146–160, January–February, 1997.     

Artificial focusing system in the ionosphere

We propose a method for the creation of an artificial focusing radio wave system in the ionospheric E layer on the basis of the recombination effect by production of a bagel-shaped disturbance region in the ionosphere in the two-dimensional case and a two-band disturbance region in the one-dimensional case. Two-band disturbance of the ionosphere was achieved by appropriate reconstruction of the antenna system of the SURA facility. First experiments on the diagnostics of a focusing ionospheric system have been performed by observations from the NASA WIND space vehicle. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, Nos. 1-2, pp. 101–110, January–February, 1997.     

Effect of an RF discharge plasma on the telemetric antenna radiation of a sounding rocket

A considerable increase in the intensity of the telemetric signal radiated from the MR 12 sounding rocket surrounded by an artificial RF discharge plasma envelope was detected in the “Aktivny Shnur” ionospheric experiment in February 1991. The experimental data are presented and their interpretation is given. Lobachevsky State University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 1, pp. 121–126, January, 1998.