Spectral characteristics of a microwave radar signal backscattered by the sea surface at small incidence angles

We present a theoretical analysis of the Doppler-spectrum properties of a microwave radar signal scattered by the sea surface at small incidence angles. The dependences of Doppler-spectrum width and shift on the wind velocity and wave development stage and their azimuthal dependence are analyzed. The case of mixed sea (wind wave plus swell) is also considered. The JONSWAP spectrum model is used to describe sea waves. The study shows that Doppler-spectrum parameters are sensitive to variation of sea-surface state; for example, for the case of developed sea waves, an increase in wind velocity by 1 m/sec leads to increases in the Doppler-spectrum width and shift by 15 Hz and 3 Hz, respectively. It is shown that for the case of a moving radar the Doppler spectrum remains sensitive to variation of sea- surface state with a sufficiently narrow radar directivity pattern. Estimates show that in the case of a single sea- wave system on the surface, using Doppler-spectrum parameters we can, in principle, determine wave type (developing wind wave, developed wind wave, or swell), dominant wavelength, wave propagation direction, and wave height; wind velocity, direction, and acceleration distance can be determined for wind waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 5, pp. 517–526, May, 1996.This paper was supported by the Russian Foundation for Fundamental Research (project 93-02-15892).     

Model of a Doppler Spectrum of Microwaves Backscattered from a Sea Surface at Small Grazing Angles

On the basis of known experimental data, we propose a model for a Doppler spectrum of a horizontally polarized 3-cm microwave signal backscattered from a sea surface at small grazing angles about 10^° for wind velocities 3-11 m/s. The model is represented as the superposition of Lorentz and Voight spectral lines with coefficients describing relative energy contributions of different scattering mechanisms as functions of the surface-wind velocity.     

Influence of the solar-wind magnetic field on the magnetosheath turbulence behind the bow shock

The experiment Sura–-WIND (1996–1997) on radio-raying of geodisturbed solar-wind region is interpreted in terms of modern knowledge of an interaction between the magnetized solar wind and the Earth's magnetosphere. Characteristics of the scattered signal at 9 MHz, determined by a plasma turbulence level with scales about 100 km, are statistically related to in situ measurements of solar wind parameters such as plasma density and the orientation and magnitude of the interplanetary magnetic field (IMF) onboard WIND spacecraft. The dependence of the scintillation index of the detected scattered signal, characterising the average turbulence level of the Earth's magnetosheath behind the bow shock, on the IMF orientation and magnitude is revealed. To verify the relation obtained, modern nonlinear correlation techniques based on the theory of artificial neural networks (ANN) are applied. The results obtained using a three-layer ANN with error backpropagation confirm an essential IMF influence on the plasma turbulence in the magnetosheath.     

On the possibility of reconstruction of wind-wave spectra from reverberation signals in two-position acoustic sounding of the ocean

Formulas are derived that relate the running energy spectrum of a surface-reverberation signal to the space spectrum of a wind wave in two-position acoustic sounding of the ocean.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 8, pp. 856–861, August, 1993.     

On the use of the multifrequency method for studying scattered fields during the antenna measurements in an anechoic chamber

We consider a method of far-zone wideband antenna measurements performed at discrete frequencies with subsequent synthesis of the tested-antenna response in the time domain for separating the useful signal and interference due to scattering. Experimental results of a study of the scattered fields arising during the measurements of characteristics of centimeter-wave horn antennas on a standard facility in an anechoic chamber are presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 12, pp. 1066–1077, December, 2004.     

Review of results of HF scattering by artificial ionospheric turbulence obtained with UTR-2 radio telescope

The results of bistatic-radar and transillumination studies of the F-layer under the influence of powerful radio waves (Sura heating facility, Nizhny Novgorod) are presented. A highly directional receiving antenna (UTR-2, Kharkov) made it possible to detect and interpret a number of fine-structure characteristics of the Doppler spectrum of a signal scattered by a heated region. It is shown that, in addition to regular drift, there exists relative ordered motion of inhomogeneities in a perturbed region. The relative velocity is estimated. Deformation of the spectrum of a scattered signal in the states of development and relaxation is established and studied, and possible mechanisms of this phenomenon are discussed. Quasi-periodic variations of the amplitude and frequency of a scattered signal with periods of 30 sec to 5 min are detected. A comparison is made with the results of simultaneous radio transillumination of a heated region by signals from the point source Cassiopeia.Scientific-Research Radio-Physics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 4, pp. 479–492, April, 1994.     

二维粗糙海面散射回波多普勒谱频移及展宽特征

基于二维线性海面模型及粗糙面电磁散射的一阶小斜率近似公式,研究了海面回波各阶多普勒谱的频移特性,得到了多普勒谱频移所对应的理论公式,与经典多普勒频移公式相比考虑到了风速、大尺度波浪轨道运动等因素对多普勒谱频移的影响;同时根据粗糙面的双尺度模型,基于多普勒谱频移的物理机理,给出了求解散射场多普勒谱展宽的理论公式.最后将理论公式计算所得结果与模拟结果及实测数据进行了比较,讨论了风速、入射波频率及入射角等因素对多普勒频移及多普勒谱展宽的影响.通过比较可以发现,给出的理论公式可以对多普勒谱频移和展宽进行一定程度的预测. 关键词： 粗糙海面 电磁散射 多普勒谱     

Estimation of surface roughness effect on spectral characteristics of tone signals propagating along stationary paths in a shallow sea

Scattering of a tonal low-frequency (up to 400 Hz) acoustic signal on a rough surface during its propagation along stationary paths in a shallow water area is considered. A calculation technique of estimating the spectral power density of the signal scattered at wind waves (reverberation) given an arbitrary angular distribution of the wind wave is developed based on the Bragg scattering model. The obtained results are compared with the results of numerical simulation of resonant sound scattering at surface perturbations according to an algorithm proposed by the authors, as well as with the results of experimental investigations.     

Spectrum of radar signal reflected from sea surface

The theoretical problem of the spectrum of a microwave radar signal reflected from the sea surface is examined with allowance for the simultaneous contributions of two scattering mechanisms — reflective and Bragg. The characteristics of the scattered-field spectrum are studied as functions of wind velocity, radar-beam angle of incidence, radar velocity, and antenna beam width. The results indicate high sensitivity of the spectrum parameters to changes in the sea-surface state.Institute of Applied Physics, Russian Academy of Science. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 1, pp. 3–15, January, 1993.     

Fourth moments of acoustic waves forward scattered by a rough ocean surface

Abstract

Three types of statistical fourth moments of acoustic waves forward scattered by a randomly rough ocean surface are derived and numerically evaluated. The first one is related to the scintillation index which characterizes intensity fluctuations. The second one is the two-position intensity correlation function which describes the spatial correlation of wave intensity. The third is the fourth-moment two-position coherence function which carries information on the phase fluctuations of the scattered wave. In the range of weak scattering, the ratio of the absolute value of the fourth-moment two-position coherence function over the two-position intensity correlation exactly describes the mean-square fluctuation of the relative phase between the two positions. The acoustic frequency is high so that the Kirchhoff approximation can be used. Two types of spectral functions for surface-height fluctuations are considered: a Gaussian spectrum and the Donelan-Pierson spectrum. The latter is obtained from a model for the fluctuations of the ocean surface height which are controlled by the wind speed at the ocean surface.     

Parametric scattering of high-frequency elastic waves by a small spherical cavity oscillating under the action of a Rayleigh wave

Scattering of high-frequency transverse and longitudinal plane waves incident on a spherical cavity located at a small depth under the surface of a half-space is considered. The cavity oscillates as a whole in the field of a low-frequency Rayleigh surface wave, the oscillation vectors of the longitudinal, transverse, and surface waves being coplanar. The cavity radius is assumed to be small compared to the wavelengths of the sounding wave and the pumping surface wave. The scattered compression and shear waves at the combination frequencies ω±Ω are calculated in the dipole approximation. Expressions obtained describe the qualitative behavior of the combination-frequency signal levels produced at the outputs of horizontally and vertically oriented geophones moving over the free surface of the elastic half-space.     

Sources of intensive noise signals of millimeter wave band

The new method of the CW intensive noise signals excitation in millimeter wave band has been studied. With this aim in mind the O-type Backward Wave Oscillators, operating in chaotic oscillation regime, are proposed to use. The noise sources, based onBWO, have a high efficiency, universal power spectrums and feasibility of electronic tuning of the noise signal frequency in the relative range of 4–10%. Low voltage noise sources, operating in the bands needed over the range from 30to 60GHz, make possible output power of 8 – 25W and 4W respectively and 3 –dB power spectrum width more than 300M H z. Application of the suitableBWO offers to excite the noise signals in decimeter and centimeter ranges too.     

Detection of gravitational waves by the method of light scattering by elastic oscillations

The scheme of gravitational wave detection which uses the phenomenon of light scattering by the elastic wave these waves cause is discussed when the presence of the gravitational waves can be judged by the presence of fine components of the scattered light spectrum. Estimates carried out show the possibility of an experimental realization of the proposed scheme.Translated from Izvestiya VUZ, Fizika, No. 3, pp. 23–27, March, 1973.     

Spectral scattering properties of a nanohole in a noble-metal film in the evanescent waves area

The effect of enhanced optical transmission through subwavelength holes and their arrays is used for multiple practical applications especially in optical antennas and local biosensors design. This effect is usually considered under excitation of plane wave propagating at the normal direction to the screen surface. In this work the effect of extreme transmission through the hole in the evanescent wave's area is in focus. The discrete sources method has been applied to analyse the spectral characteristics of light scattered by a cylindrical nanohole in a noble-metal film on a prism surface. The influence of the wavelength, incident angle, film materials and hole's filling on the scattering characteristics has been investigated. A close correlation between the effect of extreme transmission and the surface plasmon resonances has been detected.     

Fourth moments of acoustic waves forward scattered by a rough ocean surface

Three types of statistical fourth moments of acoustic waves forward scattered by a randomly rough ocean surface are derived and numerically evaluated. The first one is related to the scintillation index which characterizes intensity fluctuations. The second one is the two-position intensity correlation function which describes the spatial correlation of wave intensity. The third is the fourth-moment two-position coherence function which carries information on the phase fluctuations of the scattered wave. In the range of weak scattering, the ratio of the absolute value of the fourth-moment two-position coherence function over the two-position intensity correlation exactly describes the mean-square fluctuation of the relative phase between the two positions. The acoustic frequency is high so that the Kirchhoff approximation can be used. Two types of spectral functions for surface-height fluctuations are considered: a Gaussian spectrum and the Donelan-Pierson spectrum. The latter is obtained from a model for the fluctuations of the ocean surface height which are controlled by the wind speed at the ocean surface.     

Photodetection of coherent radiation scattered by a moving diffusely-reflecting surface,by a finite-aperture receiver

The question of the effect of the dimensions and form of the receiver aperture on the spectral properties of the photocurrent in the case of photodetection of scattered coherent radiation is studied theoretically and experimentally. It is shown that this effect is essentially different in the near and far wave zones. Formulae are obtained for the photocurrent spectra for different dimensions of receiver apertures.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 7, pp. 52–58, July, 1971.In conclusion, the authors have the pleasant task of acknowledging the assistance of E. P. Kuznetsov in preparing the experiment and of thanking I. P. Mazan'ko for his interest in the work and useful discussions.     

Scattering of a spherical wave by a statistically irregular dielectric surface

The scattering of a spherical wave by a static irregular dielectric surface, separating two subspaces with dielectric constant close to the permittivity of free space, is investigated by the Kirchhoff method. The irregularities of the surface — large-scale with small angles of inclination, and their heights are distributed according to a normal law. Self-shadowing and the set of spots associated with scattering on such a surface are taken into account. The polarization matrix of second moments of the components of the scattered field is calculated. The dependence of the matrix elements on the statistical parameters of a randomly irregular surface are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 7–10, May, 1974.     

真空中不同极化电磁波在微波等离子体喷流中的衰减特性实验研究

在真空环境中，利用空间反射电磁波测量装置，开展微波等离子体喷流对垂直和水平极化电磁波衰减的实验研究，分析不同极化电磁波在等离子体中衰减的影响因素.实验结果表明：以氩气为工质，真空室中微波等离子体喷流对垂直和水平极化电磁波具有显著的吸收效应.发生器流量、功率以及实验真空度对垂直极化电磁波在等离子体中的衰减影响明显.真空度和发生器功率对水平极化电磁波没有显著影响. 关键词： 等离子体中的电磁波 等离子体基本性质 电磁波     

New strategy for optimum design of a linear and nonlinear equalized digital fibre optic communication system

For data rates above 100 Mbits s^–1 multimode optical fibre systems are generally modal dispersion rather than loss limited and some form of equalization is highly desirable. In this paper a new strategy for the optimum design of an equalized receiver is introduced with the aim of maximizing the repeater spacing. Linear and nonlinear equalizers are briefly reviewed and their relative merits discussed. In the receiver design, Poisson signal statistics and additive Gaussian noise are considered. A new upper bound on the bit error rate which allows an adequate accuracy is proposed. Results obtained for 140 and 560 Mbits s^–1 show a noticeable increase of the repeater spacing when the proposed design strategy is introduced.     

On the theory of scattering in media having space-time fluctuations

The propagation of electromagnetic waves in nondispersive media having space-time fluctuations of the permittivity is considered. Within the framework of the method of small perturbations the effective permittivity tensor and the spectrum of the scattered field are calculated. It is shown that the presence of time fluctuations affects the energy relationships for the propagating wave. In particular, for fairly fast fluctuations the average field of the wave increases regardless of scattering.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 2, pp. 249–256, February, 1972.The authors thank N. G. Denisov, N. S. Stepanov, Yu. A. Ryzhov, and V. V. Tamoikin for their helpful discussions.