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Numerical solution of the wave parabolic equation on a rectangular grid is analyzed when the discrete split-step Fourier transform (FT) method is used to calculate the field values in an inhomogeneous medium on the next step in the range. The goal is to find out the limiting possibilities of the FT method itself, so studies have been carried out for radio wave propagation in free space only. Two related problems have been solved. First, the minimum value of the root-mean-square error (RMSE) of the calculated field has been estimated. Second, the same has been done for the transmission coefficients of the Fourier series harmonics and of the coefficients of the artificial absorbing layer (AL), which are dependent on the parameters of the computational scheme. It is shown that the dependence of the RMSE value on the distance to the source always has a maximum. The forms of the optimal ALs differ from those used conventionally primarily by the presence of a significant imaginary component.

The systems intended for detecting objects of artificial and natural origin are widely used while implementing the remote sensing methods. In this case, such different frequency ranges of sounding signals as radar, acoustic and optical ones are used. This article presents the results of patent analysis of the detection systems for such groups of the International Patent Classification as G01S13, G01S15, G01S17. The analysis has been carried out using the database of the United States Patent and Trademark Office (USPTO) inventions registered from 2015 to 2019. The aim of the given study was to compare the development trends of the object detection systems using the reflection or reradiation of radio-, acoustic or electromagnetic waves. It is shown that the proposed approach makes it possible to identify the promising (breakthrough) technological directions, as well as to form predictive estimates of their development in the short-term.

A new method is proposed to calculate the mean level of an electromagnetic field propagating along sea paths, based on a numerical solution of the parabolic equation. A way of taking the influence of waviness of the sea surface on the mean level of the field strength of the radio field is proposed. This method is based on the method of conformal mapping of a curvilinear coordinate system above the uneven sea surface onto a Cartesian coordinate system above the sea surface. A comparison with computer simulations obtained using the Monte Carlo method is carried out.

The propagation factors measured for several propagation paths above the water surface are compared with the results of calculations for two modern coverage prediction systems. In calculations, numerical values of the parameters characterizing the current state of the environment observed at moments of signal measurements are used as initial data. It is demonstrated that both systems provide good accuracy for the line-of-sight and twilight zones, but the prediction accuracy is unsatisfactory for the scatter propagation.

The goal of the paper is to find out what is the accuracy of propagation factor prediction over the beyond-the-horizon paths using the parabolic equation numerical solution. Real height profiles of temperature, pressure and humidity are used to calculate profile of the modified refractive index as the initial data. It is shown that the accuracy of prediction is satisfactory for the distance up to 300 km and it strongly depends on atmospheric conditions.

A simple radiotomography installation can be used for estimation of the thickness of an atmospheric random inhomogeneous layer located across the path. A system based on the angle antennas diversity is able to be more accurate. An additional advantage of this system is that the errors do not grow if the coherent signal processing is replaced by more simple incoherent processing.