Localization of plasma layers in the ionosphere based on observing variations in the phase and amplitude of radiowaves along the satellite-to-satellite path

We propose a method for localization of layered structures in the ionosphere, which is based on simultaneous observations of time variations in the intensity and phase of radio waves along transionospheric paths. The method determines the position of the turning point, where the gradient of the refraction index is perpendicular to the ray trajectory and the influence of the layered structure on the parameters of radio waves is maximal. The layer position is estimated by analyzing the variations in the phase and intensity of radio waves in combination. The method was used to analyze the experimental data obtained by the radio occulation mission CHAMP. The position for inclined plasma layers was determined and the electron density distribution was found for the considered radio occultation sessions. The method was verified by measuring the turning point on the ray trajectory in a neutral gas in the atmosphere. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 1, pp. 1–9, January 2008.     

Effects of low-frequency biasing on spontaneous otoacoustic emissions: amplitude modulation

The dynamic effects of low-frequency biasing on spontaneous otoacoustic emissions (SOAEs) were studied in human subjects under various signal conditions. Results showed a combined suppression and modulation of the SOAE amplitudes at high bias tone levels. Ear-canal acoustic spectra demonstrated a reduction in SOAE amplitude and growths of sidebands while increasing the bias tone level. These effects varied depending on the relative strength of the bias tone to a particular SOAE. The SOAE magnitudes were suppressed when the cochlear partition was biased in both directions. This quasi-static modulation pattern showed a shape consistent with the first derivative of a sigmoid-shaped nonlinear function. In the time domain, the SOAE amplitudes were modulated with the instantaneous phase of the bias tone. For each biasing cycle, the SOAE envelope showed two peaks each corresponded to a zero crossing of the bias tone. The temporal modulation patterns varied systematically with the level and frequency of the bias tone. These dynamic behaviors of the SOAEs are consistent with the shifting of the operating point along the nonlinear transducer function of the cochlea. The results suggest that the nonlinearity in cochlear hair cell transduction may be involved in the generation of SOAEs.     

Correlation of neural responses in the cochlear nucleus with low-frequency noise amplitude modulation of a tonal signal

The responses of single neurons of the cochlear nucleus of a grass frog to long tonal signals amplitude-modulated by repeat intervals of low-frequency noise have been studied. The carrier frequency always corresponded to the characteristic frequency of the studied cell (a range of 0.2 kHz–2 kHz); the modulated signal was noise in the ranges 0–15 Hz, 0–50 Hz, or 0–150 Hz. We obtained the correlation functions of the cyclic histogram reflecting the change in probability of a neuron pulse discharge (spike) during the modulation period with the shape of the signal envelope in the same period. The form of the obtained correlation functions usually does not change qualitatively with a change in carrier level or modulation depth; however, this could essentially depend of the frequency component of the modulating function. In the majority of cases, comparison of the cyclic histogram of the reaction with only the current amplitude value does not adequately reveal the signal’s time features that determine the reaction of a neuron. The response is also determined by the other sound features, primarily by the rate of the change in amplitude. The studied neurons differed among themselves, both in preference toward a certain range of modulated frequencies and in the features of the envelope that caused the cell’s response.     

Certain statistical characteristics of signals that are partially reflected from the D-region of the ionosphere

Experiments performed on an installation for investigating the D-region of the ionosphere by the method of partial reflections have shown that the amplitudes of the signals are distributed according to the Rayleigh law, and that the characteristic time ₀ of the amplitude fluctuations depends on the dimensions ₀ of the antenna radiation patterns. An interpretation is presented of the obtained results using the model of frozen inhomogeneities that move in the horizontal direction with a velocity v.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 4, pp. 504–509, April, 1972.The authors thank V. V. Tamoikin for his useful advice, and T. N. Fedoseev for the help that he gave in performing the calculations on the electronic computer.     

Frequency correlation of fluctuations of short-wave signals in the theory of refractive scattering of radiowaves in the ionosphere

We consider the problem of frequency correlation of phase fluctuations of HF signals reflecte from a turbulent ionospheric layer with an arbitrary profile of electron density in vertical and oblique sounding of the ionosphere. Expressions for evaluation of the coherence band of HF signals reflected from a randomly inhomogeneous ionosphere are obtained. Calculation results are compared with corresponding calculations of frequency correlation of fluctuations of HF radiowaves in Buker's theory of refractive scattering of radiowaves. It is shown, in particular, that the influence of splitting of rays for waves with different frequencies in an inhomogeneous ionosphere on the frequency distortions of HF signals prevails compared with the phenomenon of frequency decorrelation of fluctuating HF signals propagating in a free space beyond a turbulent ionospheric layer.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 9, pp. 893–900, September, 1995.     

The statistical model of the fading of shortwave radio signals that are obliquely reflected from the ionosphere

Fast fadings of a shortwave signal are simulated by a Poisson sequence of pulses. The laws governing the distribution of the amplitudes and lengths of the pulses are determined from experiments. The autocorrelation function and the distribution function of the signal levels are calculated, and a comparison is made with experiments.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 1, pp. 5–10, January, 1972.     

Study of the lower ionosphere using artificial periodic irregularities

We report on the studies of the lower ionosphere with improved height resolution using artificial periodic irregularities. This method is useful for studying the irregular structure of the ionosphere. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 9, pp. 1077–1085, September, 1998.