The article is dedicated to the problem of recovering gaps in data series of experimental long-term continuous high-frequency observations of carbon dioxide concentration and air temperature. The study was conducted using the observation results from an automatic eco-climatic station located in a tropical monsoon forest in southern Vietnam (Dong Nai biosphere reserve). Gaps in observation series are, as a rule, random and caused by technical malfunctions of the instrumentation. Accurately recovered observation series allow for the assessment of the temporal variability of observed parameters on different time scales. In the scope of this study, options for recovering the continuity of time series based on mathematical statistics methods—autoregression (ARIMA) and the linear prediction method—have been considered. A comparative analysis of the accuracy of gap recovering using different methods is provided.

The analysis of regional trends in surface air temperature has become particularly relevant in recent years due to climate changes caused by an increase in the average global air temperature. This paper evaluates the main trends of long-term dynamics and cyclical changes in the average monthly air temperature in several regions of Russia, analyzes the statistical significance and adequacy of the constructed models, presents their comparative characteristics, and provides a forecast of regional trends.

The results of simulation of the bistatic radar cross-section (RCS) of perfectly conducting bodies based on electromagnetic near-field computations are presented. The relevance of the topic is dictated by the need to measure bistatic RCS in anechoic chambers. Near fields are simulated using the FEKO software package, while only a part of the finite cylindrical scanning surface is considered, which does not completely cover the object under study. We have considered two methods for obtaining bistatic RCS patterns based on the fields calculated on the scanning surface using the Stratton–Chu formulas and by expanding the electromagnetic field in terms of cylindrical waves. The possibility of obtaining bistatic patterns in a given range of bistatic angles during measurements on the specified scanning surfaces with a radius on the order of 3–4 wavelengths is studied. The results of the both methods are compared. The scanning surface height required for the specified accuracy of the RCS pattern is determined for the scanning surface completely encircling the cylinder in the azimuthal plane.

The influence of the protective plate on the accuracy of measuring the two-position scattering diagram of the target is studied, taking into account the interaction of the target under study and a support in the form of a metal pylon with the ogival cross section. The plate is placed on a rotary support shaft and is a flat two-or three-layer structure consisting of radio-absorbing dielectric and metal layers. The plate is installed between the support and the target in order to eliminate re-reflections that occur between the support and the target. Various configurations of the plate are investigated to find its optimal parameters. A horizontal metal cylinder was chosen as the target under study, a plane electromagnetic wave of vertical or horizontal polarization with a frequency of 3 GHz is incident on the side surface of the cylinder. The possibility of reducing the error in the obtained experimental results of measuring the two-position radar cross section of targets in the possible largest angular sector is investigated. In doing so, the focus was on the most important sectors in practice. The results obtained in the course of numerical simulation of electromagnetic wave scattering showed that certain plate configurations can significantly reduce errors arising from the interaction of the support and the target. Moreover, such a decrease can be ensured in a fairly wide sector of angles that are of interest from a practical point of view.

A new method for isolating the quasi-periodic component of a time series based on the description of its form is proposed. This form is set by alternating convex up and convex down sections, the inflection points are the form parameters. The quasi-periodic component is isolated by solving the problem of the best approximation of the presented series by quasi-periodic signals. This approach makes it possible to distinguish a component with a variable period in the time series. After morphological filtration of the component of the series modeling the daily variability, the remainder of the series becomes stationary, which allows using methods of mathematical statistics and Fourier analysis for its further study. Verification of the obtained results was carried out by comparison with the results of Fourier analysis. The effectiveness of the approach is illustrated by results of decomposition of a time series of CO2 concentration in the atmosphere.

In this paper, the methods of determining the bistatic radar cross sections (RCSs) of objects by near-field measurements with the use of a cylindrical scanner and further electromagnetic far-field calculations with the use of mathematical modeling are studied. In this case, an important problem is the possibility of scanning over a truncated surface instead of scanning over the entire one. Under such conditions, the results given by the classic method [1] become poorly predictable and the application of an adapted method is required. This paper develops the method in [2] as applied to a vector three-dimensional case. Two methods based on the serial expansion in cylindrical waves in the case of scanning over a truncated surface are compared: the classic method applied for the measurement of antenna radiation patterns (when the field outside the scanning area is set equal to zero) [1] and the proposed method, which strictly takes into account a truncated character of the scanning surface by angle. The comparison of calculation results confirms the method proposed in this paper is promising for application.

The paper considers the influence of the electromagnetic interaction of the object under test with the pylon on the results of radar cross-section (RCS) measurement. Two approaches to decreasing the influence of this interaction are considered: using the shield made of radio absorbing material (RAM) and using the metal plate covered by RAM. The errors of the RCS measurement for spherical scatters and a horizontally located cylinder as a model object are obtained in the mathematical model of the experiments. The computer simulation of the RCS measurement of the object in the field of a plane electromagnetic wave is conducted using FEKO program by method of moments. The results of the simulation showed the effectiveness of application both a shield and metal plate covered by RAM.

Accurate measurements of plane wave scattering effects on various objects are necessary for modern practical electrodynamics, especially radiolocation. Compact range is a test facility designed to create a plane electromagnetic wave in a specified area. To transform electromagnetic field from a spherical wave into plane one, collimators are used. While collimator is a fundamental part of a compact range, it also acts as a source of measurement error: diffraction effects at the boundaries of the mirror distort the reflected field, increasing its inhomogeneity. These effects are significantly decreased when using collimators with rolled edges. The efficiency of the rolled edges application depends on the geometric parameters of the collimator reflector, and the best combination of these parameters can be found with mathematical modeling.

Two types of tapered anechoic chambers, conical and pyramidal, which are often used for measurements at low frequencies (up to 1 GHz), are analyzed by means of mathematical simulation. The field characteristics in the quiet zone of both chambers are compared. The electromagnetic field inside the tapered chambers is calculated using the method of moments. The dielectric lens influence on the field in the quiet zone is investigated. Characteristics of the field passing through the lens are calculated using the geometric optics method.

The paper presents the results of a study of seasonal and interannual variability of CO 2 concentration above the moist tropical forest in southern Vietnam. Experimental data were collected during year-long observation of CO 2 directly in the forest from 2012 to 2017. All data were obtained through the use of an air intake tube, placed on a metal tower at a height of 46 m and connected to a Li-Cor 820 gas analyzer (Li-Cor Inc., USA) located in a building at the foot of the tower. The values of the concentration were recorded with a resolution of 1 second; for further analysis, all data was averaged to 0.5 h values. Statistical processing based on the Fourier analysis allowed to evaluate the main characteristics of the annual distribution of CO 2 concentration, such as the amplitude and phase, as well as to analyze their variability over the years. The results of the study showed a presence of a well-determined annual course of CO 2 concentration above the canopy of the moist tropical forest.

The paper presents the results of applying the continuous wavelet analysis method to assess the cyclic components of discrete time series. The work is based on an analysis of a long-term series of data on observations of air temperature in the south-west of the Valdai Upland, as well as analysis of data on observations of CO2 concentration in the canopy of the tropical monsoon forest in southern Vietnam. The patterns of wavelet coefficients and integral spectra have been studied for all considered time series. Additionally, the cyclicities contained in the studied series were revealed.

A statistical analysis of periodic and cyclical components of time series of meteorological parameters was conducted for the 40-year observation period in the southwest of the Valdai Hills by classic seasonal decomposition and Fourier analysis. The dependence of the obtained OLS estimates of linear-regression models of meteorological parameters on a length of the smoothing interval was analyzed. Cyclical fluctuations in the time series of temperature with periods of 8 and 3 years and those of rainfall with periods of 3.5 and 10.5 years were detected and analyzed.

A numerical two-dimensional hydrodynamic model was used to describe the influence of forest belts of different sizes on turbulent transport of SO2 within the atmospheric surface layer. The results of the model calculations showed that the presence of a forest belt results in an substantial reduction of the horizontal SO2 flux due to the decrease of the wind speed and the absorption of SO2 by tree crowns. The extinction coefficient of SO2 flux increases with an increase in the forest belt size and decrease with the pollution source height.

The paper is related to the rigorous coupled-wave analysis (RCWA) for the calculation of the reflection of electromagnetic waves from a radio absorbing material (RAM). The goal of this study is, first, to check the applicability of the RCWA method for the calculation of the reflection indices of the materials used in modern anechoic chambers and, second, to evaluate its feasibility in subsequent applications for optimization of the characteristics of anechoic chambers. We shall consider the rigorous coupled-wave analysis, as well as some of its modifications: the ETMA method and the method of partial solution. The results of the calculations are given for a commercial wedge-shaped radio-absorbing material. The method of layered approximation is also considered. The approximate and exact solutions are shown to be in good agreement, including the most important case of incident angles near 90°.