Rejection of spectrally lumped noise during chirp sounding of the ionosphere

We describe a mathematical model for a signal-and-noise mixture at the output of a chirp-ionosonde receiver. A method for lumped-noise attenuation based on using the criterion of detection of rough errors in experimental measurements is proposed. The results of numerical and full-scale experiments on efficiency estimation of the proposed method are presented. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 9, pp. 751–759, September 2006.     

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.     

Monitoring of wave-like disturbances by means of oblique sounding of the ionosphere

We present the results of experimental studies of ionospheric wave-like disturbances on the basis of oblique chirp sounding data for the mid-latitude paths Cyprus-Rostov-on-Don and Inskip-Rostov-on-Don. Twenty-four-hour measurements were performed in January-May and October–November, 2005 and in January, 2006. The spectral analysis of variations in the maximum observed frequency (MOF) is performed. It is shown that the spectra of the MOF fluctuations have a well pronounced line structure. The amplitude-dominant spectral harmonics are concentrated near the frequencies 0.18–0.8 mHz (20–90-min periods). We give the results of modeling of radio waves propagation in the presence of traveling ionospheric disturbances and compare the calculated and experimental data. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radio.zika, Vol. 49, No. 12, pp. 1015–1029, December 2006.     

On the possibility of quasi-vertical radio sounding of the ionosphere in the extremely low frequency band

The experimental measurements show that the state of the ionosphere pronouncedly affects the field of the extremely low frequency (ELF) band in the transition zone. The measurements were performed on the Kola Peninsula at different times of day and in different seasons of 2006. The observed seasonal variations in the results are larger than the diurnal variations. The measured field strength does not tend to the calculated statistical value with decreasing frequency if the effect of the ionosphere is ignored. The possibility of using quasivertical radio sounding of the ionosphere in the ELF band to study the structure and electric parameters of the ionosphere is discussed.     

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.     

Electro-acoustic sounding of the atmosphere

This paper presents the results of measurement of the electrical field generated by a high-power acoustic signal in the atmosphere (electro-acoustic sounding). The radiated acoustic power was about 1 kW. The acoustic-signal frequency varied linearly within the interval 17–21 Hz with a period of 8 min. The electric field was registered by a -shaped antenna. The results of processing of the electric-field records for a part of sessions indicate the presence of an electric response with frequency close to the acoustic-signal frequency. The signal amplitude at the input of the receiving device was 0.1–1 µV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 1, pp. 33–37, January 2005.     

Radioacoustic sensing of the ionosphere

Institute of Geology and Geophysics, Siberian Branch, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 31, No. 5, pp. 537–544, May, 1988.     

Subsonic solitons in the ionosphere

The non-linear effect of self-localization of intens gravity-acoustic waves in the non-uniform ionosphere is analysed. The characteristic duration of such non-linear solitary waves is calculated. The definite connection between the non-linearity and the dispersion of the waves provides the stable character of such solitons against modulational type instabilities.     

Convergent instability in the ionosphere

A linear theory of the convergent instability (CI) of ionospheric plasma associated with the nonuniform nature of its regular motion is examined. The conditions under which CI appears in the E- and F-layers for vertical ion motion caused by various physical factors are analyzed. The possibility of small-scale strongly geomagnetic-field-aligned nonuniformities of electron concentration (l_min 10–30 m) is demonstrated. The altitude dependence of collision frequency is shown to play a large role in CI.Scientific-Research Radio-Physics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 10, pp. 921–928, October, 1993.     

Turbulence spectrum of the upper ionosphere

The problem of defining the spectral form of ionospheric irregularities with dimensions from hundreds to thousands of meters is considered. A generalized model is proposed for the ionospheric turbulence spectrum, taking into account both the anisotropic properties of the large-scale fraction of irregularities and the dependence of the anisotropy (elongation) of small-scale irregularities of the upper ionosphere along the Earth magnetic field direction on the transverse scale of those irregularities. Relations have been derived to determine the basic parameters of the irregularity spectrum of the uppers ionosphere (anisotropy indices for large-scale and small-scale fractions) and the depth of a thin ionospheric layer through measurement of the spectral characteristics of amplitude and phase fluctuations of orbital satellite signals. Using this model of the plasma irregularity spectrum, we can explain consistently many well-known experimental data on spectral characteristics of the phase and amplitude fluctuations of orbital satellite signals both in the high-latitude and midlatitude ionosphere. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 446–456, April, 1997.     

Electroacoustic atmospheric sounding

Radiophysics Scientific-Research Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 1, pp. 15–23, January, 1992.