Detection of a Chirp Ionosonde Signal under Conditions of a Priori Non-Parametric Uncertainty

Radiophysics and Quantum Electronics - We consider the model of a mixture of probability distributions for background and target samples in the problem of extracting a signal from radiophysical...     

Analysis of the Dispersion Characteristic Features of Radio Channels Using a Chirp Ionosonde

We show that stationary points of the dispersion characteristics of ionospheric HF radio channels can appear due to the effect of irregularities with scales l 2-5 km and relative variations N/N 10^-3 of electron density. These stationary points can give rise to peaks of the impulse characteristics of wideband HF radio channels. Analytical formulas for estimation of the position, height, and duration of a peak are obtained. We develop and test experimentally methods for determination of the impulse characteristics of ionospheric HF radio channels with various operating frequencies and passbands using chirp-ionosonde signals as well as methods for estimation of the parameters l and N/N of ionospheric irregularities.     

Measurement of the Doppler Frequency Shift on Individual Rays Using a Chirp Ionosonde

We develop theoretically a method for determining the Doppler frequency shift on individual rays in ionospheric sounding. The method is based on using periodic chirp signals. The potential resolution and range of the measured Doppler-shifted frequencies are determined. Application of this method yields the relationship between the Doppler shift of the propagation-mode frequency and the velocity of a horizontal displacement of the hop tops along the Khabarovsk-Yoshkar-Ola radio path. Significant correlations between the mode order in the ionosphere and the Doppler shift, Doppler-spectrum width, and stationarity time of the propagation channel are found.     

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.     

The Features of Round-the-World Signal Propagation over the Paths of the Russian Chirp-Sounder Network during Low and Mild Solar Activity

We present the results of observations of round-the-world (RTW) signals by the Russian chirp-sounder network in 1997-1999. The frequency-time intervals of the RTW propagation with minimum attenuation are determined. Using numerical simulations of HF signals based on the waveguide and geometric-optical approaches, we perform the interpretation of the experimental data. It is shown that RTW-signal attenuation is mainly determined by the state of the low-latitude ionosphere in African and Asian-Pacific longitude regions. The possibilities of monitoring large-scale structures of the low-latitude ionosphere in regions poorly equipped with diagnostic tools using the RTW-signal characteristics of the Russian chirp-sounder network are discussed.