Vol 60, No 4 (2017)

We present the results of experimental studies of the parameters of HF-enhanced ion–acoustic and Langmuir plasma waves, as well as small-scale artificial field-aligned irregularities (AFAIs) when the EISCAT/Heating effective radiated power is varied from 10 to 560 MW. In the course of the experiments, a high-power HF radio wave with the alternating ordinary (O-mode) and extraordinary (X-mode) polarizations was radiated towards the magnetic zenith at a frequency of 7.953 MHz lying below the cutoff frequency of the F₂ layer. A fundamental difference in the development of artificial ion–acoustic and Langmuir turbulence, which is seen as HF-enhanced ion and plasma lines in the EISCAT spectra, under the O- and X-mode HF pumping was found. The minimum values of the HF pump-wave electric fields in the ionosphere when the HF-enhanced ion and plasma lines, as well as small-scale artificial field-aligned irregularities, start to be excited, were determined from experimental data both for the O- and X-mode HF pumping. Comparison between the experimental and theoretical threshold values of the electric field required for the excitation of artificial ionospheric turbulence in thermal, Langmuir, and ion–acoustic modes in the high-latitude ionospheric F₂ layer for the O-mode HF pump wave was made.

By virtue of their all-weather capabilities, the radiophysical atmospheric sensing methods allow one, in particular, to perform continuous observations of variations in the atmospheric content of water vapor being the most important natural greenhouse gas. The measurement station of St. Petersburg State University at Peterhof (59.88° N, 29.83° E) runs a number of ground-based instruments to determine total water-vapor content (TWVC) in the atmosphere. During a year period from September 2014 to September 2015, the TWVC was synchronously measured by two radiophysical methods, namely, the microwave and radio-refraction techniques, as well as the optical infrared method. Comparisons show that the average systematic and random discrepancies among the three methods amount to 0.3–0.5 kg/m² (3–7%) and 0.4–0.6 kg/m² (8–11%), respectively. The maximum relative differences (up to 20%) among the results of different-type measurements are observed for very small TWVC values (below 5 kg/m²). Empirical estimates of the random errors of the methods were 0.5, 0.3, and 0.3 kg/m² for the radio-refraction, microwave, and infrared methods, respectively. The results of the TWVC measuring by the radio-refraction and microwave methods are in good agreement and yield greater values than those obtained by the optical method. The obtained discrepancies in the TWVC estimates are small compared with the published results of similar comparisons, which can, in particular, be attributed to the high spatiotemporal matching of various measurements.

We consider the weak localization and the backscattering halo in media with strongly elongated scattering indicatrices. The earlier theory is generalized to the case of a nonuniform backscattering cross section in the rear hemisphere. Asymptotic formulas for the backscattering intensities are obtained in the low-angle diffusion approximation.

We propose an energy-like detector of signals and analyze its efficiency by an example of detecting a Gaussian signal with zero mathematical expectation and uncorrelated readouts against the background of Likhter noise with independent readouts. Analytical expressions for the probability of correct detection are obtained and statistical simulation is performed. Using particular examples, we show that the energy-like detection characteristics can be much closer to the optimal ones than those of the energy detection.