Vol 62, No 3 (2019)

We present a method for automatic search and parameterization of discrete elements of very low-frequency (VLF) chorus emissions. The method is based on the processing of dynamic spectrograms using a special scanning algorithm, which is intended for seeking the discrete elements of VLF chorus emissions and calculation of their parameters. We propose to create the optimal dynamic spectrograms for the scanning algorithm by using short-time Fourier transform. The paper gives general recommendations for calculation of spectrograms and their preprocessing. The scanning algorithm is based on processing of the dynamic-spectrogram images by using the methods of mathematical morphology. The developed method was tested for several cases of chorus emissions observed by the Van Allen Probes spacecraft. It is shown that the total errors related to “false positive” detection and missing the target are about 10% of the elements visible to the human eye when the optimal parameters of the scanning algorithm are used and intense discrete elements are processed. The method can be applied to both spacecraft and ground-based wave data. The results of using the method can be employed for verification of physical theories of the formation of chorus emissions and determining their statistical properties.

In order to separate global and local effects of atmospheric electricity, measurements of the fair-weather electric field were performed in Nizhny Novgorod in 2013-2018. As a result of processing 139 diurnal records from four observation points spaced 6–8 km apart, diurnal variations in the fair-weather atmospheric electric field for different seasons and weekdays (working days and weekends) were studied. The curve of the local diurnal variation is shown to always have two maxima. The evening maximum of the diurnal variation (19:00–20:00 UT) coincides in time with the maximum of the Carnegie curve, which is a characteristic of the global electrical circuit. The highest values of the field amplitude are reached in the winter period. The field-intensity maximum in the first half of the day (09:00–11:00 LT) is characteristic of the urban environment and shows that local effects associated with the presence of aerosol particles in the air significantly contribute to the formation of diurnal variation, especially in summer. According to the 2013–2018 measurements, the seasonal variation in the monthly-average values of the atmospheric electric field is revealed and analyzed compared with the results of measurements of seasonal variation in other regions of the globe. The obtained results allow one to reveal the role of local effects in the formation of diurnal variation in the mid-latitude areas with temperate continental climate and provide a basis for developing a theory which can explain the physical mechanisms of local effects and suggest appropriate parametrization for finding the surface electric field in the weather and climate models.

We estimate geoacoustic parameters of a layered bottom in a shallow waveguide, which is nonuniform along the path, using the data of the full-scale experiment and the matched-field method. On the basis of the available a priori geological and geophysical data, a waveguide consisting of two sedimentary layers and the underlying half-space is used as the reference geoacoustic model. When seeking the geoacoustic parameters corresponding to the global minimum of the objective function, the hybrid algorithm, which is a combination of the fast simulated annealing method and the Hook–Jeeves method of direct search, is used.

We propose a quasioptimal method of separate optimization in a multistage relay MIMO system, which is based on optimization of the root-mean-square error between the input and output signals successively for each transmission stage. Rigorous analytical expressions for the spatial coding and decoding matrices are obtained. Separate optimization simplifies the system construction due to a significant reduction in the number of auxiliary (service) communication links, which are necessary for transmitting the channel information, compared with the joint optimization. The simulation results show the high efficiency of the proposed method.