V. G. Galushko

Traveling ionospheric disturbance diagnostics using HF signal trajectory parameter variations

In the model of a perfectly reflecting surface the inverse problem of restoring dynamic and statistical parameters of traveling ionospheric disturbances (TIDs) from variations of angles of arrival and Doppler frequency shift of HF radio signals on one-hop oblique radio paths is solved. The technique for determining dispersion law, fluctuation spectrum, geometry, direction, and velocity of TID motion is described.

Non-linear interaction between Schumann resonances and HF signals

Abstract The effect of cross-modulation between Schumann resonances (SR) and HF (15 MHz) roundthe-world signals (RWS) has been established experimentally. The peaks near the frequencies 8, 14, 20 Hz were discovered in the spectra of the RWS. These maxima correspond to three first modes of SR. A theoretical model which explains the effect of cross-modulation is proposed. The interaction of the signals is due to the electron heating by SR fields in the D-layer of the ionosphere. This leads in its turn to the modulation of the electron collision frequency and to the attenuation of RWS. It is essential that the fair weather electric field in the ionosphere is taken into account. The influence of this field leads to a linear dependence of the electron temperature variations on the field strength of SR.

Doppler Selection of HF Radiosignals on Long Paths

The long-term registration of the Doppler spectra of HF radiosignals has been performed on the Moscow-Akademik Vernadsky Ukrainian Antarctic station path. It has been revealed that the spectra are split when the solar terminator crosses direct and return radio lines. The spectral and energy characteristics of direct and return signals have been calculated within the scope of the asymptotic theory of long-range propagation of decametric radiowaves.

Ionospheric diagnostics using wave field diffraction near the caustic

Results of investigating the spatial and temporal HF field structure near the skip distance are presented. The data were obtained on midlatitude radio paths less than 1000 km in length, using broadcasting stations as sources of the probe signals. The signals reflected by the ionosphere were received and processed with a multichannel coherent receiver and the largest phased array of the decameter radio telescope UTR-2. The strong dependence of the probe signal parameters on the ionospheric plasma conditions has allowed formulating and solving a number of model inverse problems of ionospheric diagnostics. It proves possible to determine parameters of the parabolic ionospheric layer, and the effective electron collision frequency, to evaluate horizontal gradients of the electron density and some parameters of the medium-scale-size ionospheric irregularities. A number of tests made both within the method and by means of comparison of the restored parameters against the data of other diagnostic techniques demonstrate the high potential and accuracy of the approach described in the paper.

Analysis of the CA CFAR algorithm as applied to detection of stationary Gaussian signals against a normal noise background

The problem of radar signal detection against unknown or time variable noise background is discussed. Performance characteristics of the cell-averaging constant false alarm rate (CA CFAR) algorithm are considered as applied to detection of a stationary Gaussian signal against a normal noise background. Specifically, the detection probability is analyzed in dependence on the number of the reference cells and signal-to-noise ratio. Recommendations are presented as for selecting the optimum number of the reference and guard cells.

A two-stage procedure of radar target detection

A two-stage procedure is suggested for detection of radar targets against a noise background using a sequence of radar echoes from a spatial cell under test. According to the procedure a standard decision making procedure is first applied to each sample. Then the final “target-present” decision is taken if the detection threshold is exceeded in no less than a preset quantity of the total number of the radar samples under analysis. Expressions for the detection probability and false alarm rate are presented. Performance characteristics of the suggested algorithm are analyzed for the case of detection of stationary Gaussian signals against a normal noise background. It is shown that under certain conditions the developed technique provides an improvement in the signal-to-noise ratio as compared with the coherent and incoherent averaging techniques.