USING STEALTH TECHNOLOGIES IN MOBILE ROBOTIC COMPLEXES AND METHODS OF DETECTION OF LOW-SIGHTED OBJECTS

The paper outlines the latest technologies used by the world's leading manufacturers in the development of mobile low-observable robotic systems and promising measures to improve the quality of components and design of such objects. Methods of detecting objects using stealth technologies are considered, and it is shown that only due to a system approach it is possible to compensate for the reduction of the effective scattering surface of low-observable objects by technical means of radar stations. It is shown that the main method of increasing the range to the radio horizont is the use of an air-based radar. Methods of detecting objects on the traces of their interaction with the environment are promising for organization of cooperation of several radars in the detection of low-observable objects.

STUDY OF THE INFLUENCE OF THE TILT ANGLE OF VERTICAL STABILIZERS OF AN AIRCRAFT ON THE EFFECTIVE SCATTERING SURFACE

Рассматривается зависимость значения эффективной площади рассеяния (ЭПР) самолета от угла наклона вертикальных стабилизаторов. Моделирование производится с использованием метода геометрической теории дифракции и физической оптики, так как размеры объекта во много раз превосходят размеры длины волны. Для облучения использовалась плоская волна X-диапазона - частота 10 ГГц. По полученным результатам отражения электромагнитной волны от объекта были построены диаграммы обратного рассеяния, на основе которых была сформирована таблица, содержащая максимальные значения эффективной площади рассеяния. Было замечено, что максимальное значение эффективной площади рассеяния возникает в ситуации, когда отсутствует какой-либо наклон вертикальных стабилизаторов, и при изменении угла наклона вертикальных стабилизаторов на 5 градусов наблюдается значительное понижение максимального уровня ЭПР. При этом возможно возникновение повторных отражений от горизонтальных хвостовых стабилизаторов, что, в свою очередь, приведет к повышению уровня эффективной площади рассеяния. Грамотная оптимизация угла наклона вертикальных стабилизаторов самолета позволяет добиться значительного снижения уровня ЭПР при сохранении аэродинамических характеристик самолета, а внедрение специальных композитных стелс материалов позволяет еще сильнее понизить уровень ЭПР The article considers the dependence of the value of the effective scattering area (ESA) of the aircraft on the tilt angle of the vertical stabilizers. Modeling is performed using the method of the geometric theory of diffraction and physical optics since the dimensions of the object are many times larger than the dimensions of the wavelength. For irradiation, an X-band plane wave was used - a frequency of 10 GHz. Based on the results of the reflection of the electromagnetic wave from the object, backscatter diagrams were built, on the basis of which a table was formed containing the maximum values of the effective scattering area. It was noted that the maximum value of the effective scattering surface occurs in a situation where there is no inclination of the vertical stabilizers, while when the angle of inclination of the vertical stabilizers is changed by 5 degrees, a significant decrease in the maximum ESA level is observed. In this case, repeated reflections from horizontal tail stabilizers may occur, which, in turn, will lead to an increase in the level of the effective scattering surface. Competent optimization of the angle of inclination of the vertical stabilizers of the aircraft allows one to achieve a significant decrease in the ESA level while maintaining the aerodynamic characteristics of the aircraft, and the introduction of special composite stealth materials allows one to further reduce the ESA level

The influence of a fallacy in specific effective scattering surface evaluation on the result of double-frequency retrieval of rain intensity

Subject and Purpose. The amount of precipitation is important information for the agro-climatic justification of agro-technical and reclamation actions directly controlling crop yields. The inverse problem of rain intensity retrieval from the remote sensing data is an incorrect mathematical physical problem described by a nonlinear integral equation. The purpose of this work is to analyze how errors in the specific effective scattering surface evaluation affect the results of double-frequency retrieval of the rain intensity obtained through the inverse problem solution by the previously proposed method. Methods and Methodology. Numerical simulation by using an approach based on regularization techniques and intended for the integral scattering equation solution is carried out for double-frequency sensing in the microwave range Results. Numerical simulations of the rain intensity retrieval have been performed at the operating wavelengths 0.82 and 3.2 cm in the range 1…30 mm/h and for different values of received power errors. It has been shown that an error in the specific effective scattering surface evaluation has a greater effect on the reliability of the intensity retrieval in the shorter wavelength case. And it exerts practically no effect (not exceeding 5 %) at the longer wavelength and at the rain intensity below 15 mm/h, which, however, is true for heavier rains, too. Conclusion. The analysis of the results has shown that the error of the rain intensity retrieval remains within acceptable limits (below 20 %) provided that the error in the specific effective scattering surface evaluation does not exceed 15 % at the shorter wavelength. At the longer wavelength, it can reach 30 %.

Measurement of sea wave height by radar sounding with polarizationmodulated signals

Methods for determining the height of sea waves, which are relevant for maritime navigation, have been investigated. The measurement of the height of sea waves by the method of radar sounding by polarization-modulated signals is considered. The energy and spectral characteristics of the radar signal reflected by the sea surface at low angles of incidence are described. An algorithm for calculating the average wave height based on the results of measuring the polarization anisotropy of the specific effective scattering surface of the sea area is considered. The relation of the average frequency of the amplitude fluctuations of the reflected radar signals with the sea waves is given. The spectral characteristics of radar signals reflected by the sea surface when irradiated with polarization-modulated signals are analyzed. The procedure for forming an effective statistical estimate of the average wave height based on the results of spectral measurements is considered. The errors of the generated estimates of the wave height associated with the measurement errors of the polarization anisotropy of the effective scattering surface and the average frequency of the envelope of the amplitude fluctuations caused by the Doppler effect are analyzed. The results of experimental measurements of the spectra of the amplitude fluctuations of the envelope of the reflected signals at different states of the sea surface are presented. The analytical dependence of the polarization anisotropy of the effective sea scattering surface on the irradiation angle relative to the wave propagation direction is given. A comparison of estimates of the height of sea waves obtained from radar sounding and meteorological observation data is carried out.

STUDY OF THE INFLUENCE OF DIELECTRIC PERMEABILITY OF THE MATERIAL ON THE RADAR COSS SECTION

В качестве объекта исследования эффективной поверхности рассеяния рассматривается сфера из диэлектрического материала, у которого можно в процессе моделирования изменять диэлектрическую проницаемость среды. Для моделирования был выбран широкий диапазон частот, чтобы можно было отследить влияние отношения длины волны к радиусу сферы, а также смещение максимального значения эффективной площади рассеяния (ЭПР) объекта после изменения диэлектрической проницаемости среды. По полученным результатам было доказано, что невозможно обеспечить низкий уровень ЭПР в очень широкой полосе частот, так как если размер длины волны становится близок с размерами тела, происходит резкий всплеск уровня ЭПР. Также в процессе моделирования было доказано, что повышение диэлектрической проницаемости среды приводит к повышению максимальных значений ЭПР объекта, а также смещение этого пика вниз по частоте. По полученным графикам моностатической ЭПР можно сделать вывод, что применение сложных частотозависимых материалов позволяет добиться значительного снижения эффективной площади рассеяния даже в ситуации, когда объект становится геометрически крупным, то есть сравнимым с длиной волны. Данные сложные материалы применяются в качестве стелс-покрытия In the article, a sphere of dielectric material is considered as an object of study of the effective scattering surface, in which the dielectric constant of the medium can be changed during the simulation. A wide range of frequencies was chosen for modeling so that the influence of the ratio of the wavelength to the radius of the sphere, as well as the shift of the maximum RCS value of the object after changing the dielectric constant of the medium, could be tracked. According to the results, it was proved that it is impossible to provide a low RCS level in a very wide frequency band, since if the wavelength becomes close to the body size, a sharp surge in the RCS level occurs. It was also proved during the modeling process that an increase in the dielectric constant of the medium leads to an increase in the maximum RCS of the object, as well as a shift of this peak down in frequency. According to the obtained graphs of a monostatic RCS, it can be concluded that the use of complex frequency-dependent materials allows one to achieve a significant decrease in the effective scattering area even in a situation when the object becomes geometrically large, that is, comparable to the wavelength. These complex materials are used as a stealth coating

Simulation of the satellite radar altimeter sea ice thickness retrieval uncertainty

Although it is well known that radar waves penetrate into snow and sea ice, the exact mechanisms for radar-altimeter scattering and its link to the depth of the effective scattering surface from sea ice are still unknown. Previously proposed mechanisms linked the snow ice interface, i.e. the dominating scattering horizon, directly with the depth of the effective scattering surface. However, simulations using a multilayer radar scattering model show that the effective scattering surface is affected by snow-cover and ice properties. With the coming Cryosat-2 (planned launch 2009) satellite radar altimeter it is proposed that sea ice thickness can be derived by measuring its freeboard. In this study we evaluate the radar altimeter sea ice thickness retrieval uncertainty in terms of floe buoyancy, radar penetration and ice type distribution using both a scattering model and ''Archimedes' principle''. The effect of the snow cover on the floe buoyancy and the radar penetration and on the ice cover spatial and temporal variability is assessed from field campaign measurements in the Arctic and Antarctic. In addition to these well known uncertainties we use high resolution RADARSAT SAR data to simulate errors due to the variability of the effective scattering surface as a result of the sub-footprint spatial backscatter and elevation distribution sometimes called preferential sampling. In particular in areas where ridges represent a significant part of the ice volume (e.g. the Lincoln Sea) the simulated altimeter thickness estimate is lower than the real average footprint thickness. This means that the errors are large, yet manageable if the relevant quantities are known a priori. A discussion of the radar altimeter ice thickness retrieval uncertainties concludes the paper.