Kosharskyi V. The method of polarization selection of power lines in a helicopter radar

The dissertation is aimed at developing and researching a method for polarization selection of power lines observed against the background of the underlying surface to enhance the safety of low-altitude helicopter flights. The proposed method and algorithm are suggested to be used as an addition to onboard radars to improve the safety of low-altitude helicopter flights. Thus, the objective of the research is to enhance the safety of low-altitude helicopter flights by creating an optimal method for polarization selection of power lines, regardless of their observation angle. The object of the research is the polarization characteristics of radar signals reflected by the underlying surface and low-visibility radar objects. The subject of the research is the methods and algorithms for polarization selection of power lines against the background of the earth's surface in an onboard radar to enhance the safety of low-altitude helicopter flights. The necessity for conducting this research is related to the risks of collisions with power lines (PWL), poles, towers, buildings, and trees during low-altitude helicopter operations, regardless of their observation angle. Currently, research and development of new methods for detecting power lines are being carried out worldwide. However, most of the existing methods that are not radar-based have a low probability of detecting objects under adverse weather conditions (rain, fog, snow, etc.) and during night flights, which poses a danger to crew members and passengers. Radar methods and algorithms currently under development are based on the use of polarization characteristics of signals. The main problem with such systems, methods, and algorithms is the presence of interference along with the useful signal. This problem is proposed to be solved by synthesizing a method of polarization selection, as it will allow distinguishing observation objects against the background of interference. To achieve the goal of the dissertation, several tasks were accomplished. First of all, the polarization characteristics of power lines were studied in an anechoic chamber, examining their dependence on the frequency of the probing signal and the observation angle. The obtained experimental results form the basis for further solving the problem of polarization selection of power lines. Studies of wire samples with different diameters showed that there is a dependence between the wire diameter, observation angle, polarization of the signal, and effective scattering area emitted by the transmitter. The study of the effective scattering area (ESA) of electrical wire samples of different diameters showed that their ESA depends on their thickness, observation angle, and the polarization of the probing signal. When designing radars for power line detection, it should be taken into account that the specific ESA of wires is significantly smaller than the ESA of power line wires, poles, towers, etc. Therefore, it is necessary to use methods of polarization selection of research objects against the background of the underlying surface. Based on the criterion of maximum likelihood function, an optimal method for polarization selection of signals in a helicopter radar has been synthesized. The feature of the obtained method is that it takes into account the adaptation coefficient and the correlation coefficient between the vertical and horizontal components of the received signal. Coefficients characterizing the efficiency of polarization selection with triple compensation of passive interference depending on the electrophysical properties of the underlying surface and the detection object have been obtained. Simulated modeling of radar signals in the 3 mm wavelength range, reflected by the underlying surface and low-visibility polarization-anisotropic objects, has been conducted. The obtained simulation model takes into account the polarization of the probing signals, electrophysical properties, and geometric characteristics of the underlying surface. Simulated modeling of the polarization selection algorithm for low-visibility objects with triple adaptive interference compensation has been performed. The results demonstrate the overall functionality of the synthesized method for polarization selection of power lines.