A Re-Examination of Radar Terrain Backscattering at Nadir

The theoretical behavior of nadir specular and diffuse radar backscattering from rough terrain is re-examined. Terrain is modeled as a random rough surface in the Kirchhoff approximation. The relative significance of specular (coherent) and diffuse (noncoherent) radar backscatter is compared in terms of the antenna system parameters (beamwidth, height, and frequency) and rough surface statistics. It has been found that in case of a high-altitude (space or airborne) radar, the ratio between coherent and noncoherent terrain backscatter is independent of its altitude of the radar platform. A possible explanation is suggested for the anomalous radar backscatter observed in the Skylab S-193 altimeter experiment.     

低空雷达导引头海面目标检测性能分析

该文以雷达导引头低空检测海面目标为背景,综合分析了多径环境和海杂波环境对雷达导引头目标检测的影响。通过对目标回波、多径散射的镜反射、漫反射以及海杂波进行建模,结合具体场景,仿真分析了镜反射、漫反射以及海杂波对雷达导引头接收信号的影响,进而分析了多径散射和海杂波对雷达导引头检测不同大小目标时检测性能的影响效果。仿真结果表明:雷达导引头检测RCS低于1 m2的小目标时,海杂波是影响雷达导引头检测性能的主要因素;雷达导引头检测RCS大于10 m2的目标时,多径效应是影响雷达导引头检测性能的主要因素;雷达导引头检测RCS大于104 m2的目标时,雷达导引头的检测性能不受海杂波和多径效应影响。     

雷达低空目标闭环跟踪的C2-偏差补偿算法研究

在单脉冲测角体制下,由于多径回波信号的干扰,极大地降低了雷达低空目标俯仰角测量精度.通过对多路径反射环境模型分析,同时考虑镜面反射和漫反射的干扰,得出了岸、海基单脉冲雷达低空目标跟踪时俯仰角测量误差的产生原因,将传统的多目标分辨算法(C2算法)与偏差补偿技术相结合应用于低角多径环境下目标俯仰角的测量,弥补两种算法各自的不足.在给定的测量环境下对不同高度目标进行了仿真,得到良好的仿真结果,表明两种算法结合使用,可较大地提高低空目标俯仰角的测量精度.     

低角雷达跟踪时的多路径散射模型

要提高低角雷达跟踪目标的精度,就需要考虑由于地、海表面反射而产生的多径效应的影响.需要弄清产生多径效应的环境和条件,建立多径效应的数学模型,以便采取合理的方法进行抑制.本文给出了镜反射和漫散射引起的多径效应的代表性模型,以及考虑表面粗糙度、遮蔽效应等影响的修正粗糙面漫散射模型.     

C2动态相位估计的偏差补偿算法——雷达低空目标俯仰角测量提取的研究与应用

由于多径回波信号的干扰,极大地影响了雷达对低空目标俯仰角的测量,且对低空目标俯仰角的闭环跟踪测量实现极为困难,通常采用偏轴跟踪技术。通过对多路径反射环境模型分析,同时考虑镜面反射和漫反射的干扰,得出了岸、海基单脉冲雷达低空目标跟踪时俯仰角测量误差的产生原因,将传统的多目标分辨算法(C~2算法)与偏差补偿技术相结合应用于低角多径环境下偏轴跟踪目标俯仰角的测量,由C~2算法代替偏差补偿算法的航迹滤波并且动态估计直射和反射路径的相位差,然后对单脉冲比进行补偿,弥补两种算法各自的不足。在给定的测量环境下对不同高度目标进行了仿真,得到良好的仿真结果,表明C~2动态相位估计的偏差补偿算法,可较大地提高低空目标偏轴跟踪俯仰角的测量精度。并将其应用于某次试验中对掠海巡航飞行目标俯仰角的事后提取,与雷达实时输出的俯仰角测量数据相对比,验证了该算法的有效性和可实施性。     

A model for the imaging of urban areas by synthetic aperture radar

A numerical model developed to simulate synthetic aperture radar images of urban targets is described. The model is based on ray tracing and is designed to simulate the effects of strong specular scatterers such as corner cubes as well as the diffuse scatter from the rough surfaces of buildings. The model uses a vectorial approach to the electromagnetic fields and so is able to simulate the polarization dependence of the images. An example of the model is given, and the validation and future development of the model are discussed     

Analytical study of carrier photogeneration and photocurrent inthin silicon solar cells with specular and diffuse back reflection

An analytical study of the effect of back reflection in thin silicon solar cells implementing a practical (nonideal) diffuse reflector at the back side is presented. Both the diffuse and specular reflection components are considered. The reflection properties of the back reflector are described by means of three parameters, which are interpreted in terms of a simple physical model. An exact expression for the generation profile resulting from specular and diffuse reflections is derived and its dependence on the reflector parameters is studied. A mechanism through which specular reflection can significantly enhance light trapping in the case of relatively weak diffuse reflection is proposed. The photocurrent boost doe to both types of reflections acting simultaneously is estimated     

适于多种反射现象的光照估计方法

增强现实技术是将虚拟物体叠加到真实环境中,为了使虚拟物体更逼真地融入到环境,就需要估计场景中的真实光照。文中针对同时存在漫反射和镜面反射的场景或只存在漫反射的场景,提出了一种适于多种反射现象的光照估计方法。该方法使用相机拍摄多幅视角图像,通过检测每幅视角图像的镜面高光点来识别场景中是否存在镜面反射。若不存在镜面反射,则采用单张漫反射图像估计光照算法进行多幅视角图像光照估计。反之,若存在镜面反射则以镜面反射提供的信息为先验知识,再结合漫反射光照估计方法得到最终的光照估计结果。实验结果表明,文中方法提高了多种反射现象的光照估计的准确性。     

Error probability of m-ary fsk with a limiter-discriminator detector in satellite mobile channels

We derive formulae for the error probability of M-ary frequency shift keying with a limiter-discriminator detector in a satellite mobile channel, which includes as special cases the land mobile (Rayleigh) channel and the Gaussian channel. The received signal in this channel is composed of a specular signal, a diffuse signal and white Gaussian noise; hence the composite signal is fading with a Rician envelope. The error probability depends on the signal-to-noise ratio, the power ratio of the specular and diffuse components, the frequency deviation, the Doppler frequency, the maximum Doppler frequency, the time delay between diffuse and specular components, the autocorrelation of the diffuse component and the transfer function of the receive filter. Numerical results are presented as functions of the various parameters. Effects of the receive filter on the signal dependent components are neglected.     

A simulation for spaceborne SAR imagery of a distributed, movingscene

A computer simulation that is designed to represent aspects of spaceborn synthetic-aperture radar (SAR) imagery of the ocean surface is presented. The simulation is unique in that a scatterer density (per resolution cell) is explicitly included, thus allowing the incorporation of various scattering natures, from purely specular to purely diffuse. The simulation may be applied to ocean surface wave imaging, since velocity bunching and scene coherence times are also included. Certain assumptions inherent in the velocity bunching formulation limit the applicability of the simulation in its present form to spaceborn SAR systems only. Two experiments based on this simulation are considered: (1) the effect of varying the target density; and (2) the effect of the mean scene coherence time in the imaging of a ocean swell system     

Control of Specular and Diffuse Reflection of Light Using Particle Self‐Assembly at the Polymer and Metal Interface

We present a novel method of controlling the specular and diffuse reflection of light by the electrostatic deposition of a spherical particle monolayer followed by electroless plating. Charged polystyrene colloidal particles, ranging in size from 100 nm to 5 μm, were adsorbed from solution onto oppositely charged polyelectrolyte multilayers (PEM). The monodisperse particle monolayers were coated with nickel in a two‐step electroless plating process using palladium catalysts. These surfaces can be used as diffusive metal reflectors with a uniformly controlled surface roughness due to the uniform size of deposited particles. In addition, the self‐assembled particles at the polymer and metal interface deflected the internal stresses that build‐up at the interface while the metal was being deposited. This allowed a thicker metal film to be deposited before delamination occurred. A UV‐VIS spectrometer with movable fiber optic cables was employed to characterize the optical properties of the reflectors. The optical fibers permit versatile and precise measurements of specular and diffuse reflectance. By measuring the angular dependent reflectance, we demonstrate how to estimate the distribution of reflected light from the nickel coated surface and how to calculate the ratio of specular and diffuse reflection in the total reflected light. Optical measurements of our nickel samples showed that this approach could be used to control the portion of diffuse reflection from 8.25 to 59.97 %. Additionally, a quartz crystal microbalance was employed to study the electroless nickel plating rate on PEM. Our proposed method is simple, cost‐effective and convenient for mass production because the process consists of a series of simple immersion steps without vacuum technology or special equipment.     

GMSK with limiter discriminator detection in satellite mobilechannel

Formulas are derived to find the error probability of partial-response frequency-shift keying with limiter discriminator detection, with and without decision feedback, for a satellite-mobile channel. The special cases of a Gaussian channel and a land-mobile channel are discussed. The formulas are applied to Gaussian minimum shift keying, and the error probability is computed as a function of energy-to-noise ratio, Gaussian filter bandwidth, Doppler frequency, maximum Doppler frequency, the ratio of powers in the specular and diffuse signal components, and the time delay between specular diffuse components     

On the surface photovoltaic effect in a multivalley semiconductor in an external magnetic field

A theory of the photovoltaic effect in a semi-infinite multvalley semiconductor upon the absorption of polarized light at free carriers caused by the specular reflection and diffuse scattering of electrons at a film surface is developed by us. The kinetic Boltzmann equation in the approximation of time relaxation and boundary conditions, which determine the correlation between the distribution function of electrons reflected from a semi-infinite crystal surface and the distribution function of electrons incident onto a surface for the case of both specular reflection and diffuse scattering is used. The aforementioned takes into account the fact that the distribution function of electrons diffusely scattered from a surface depends only on their energy and is determined from the condition of total electron flux vanishing at the surface. Expressions for analyzing the spectral dependence of the current which is linearly dependent on the magnetic-field strength are obtained.     

Millimeter-wave specular and diffuse multipath components ofterrain

Multipath interference data were obtained at a frequency of 95 GHz over pathlengths of 100-250 m by measuring height-gain interference patterns over various types of terrain. Data were collected over grass, lake, ice, snow, concrete, asphalt, and gravel surfaces. The transmit antenna was kept fixed, while the receive antenna translated vertically resulting in grazing angles between approximately 0.5-2.0°. Full illumination of the Fresnel zones was accomplished by broad-beamwidth horn antennas at both ends, Measured interference patterns indicate the presence of both specular and diffuse multipath components. A technique was developed to separate these components by filtering in the spatial Fourier-transform domain by appropriate choice of the notch frequency for the specular component and the bandpass-filter bandwidth for the diffuse components. The notch frequency is chosen according to system geometry considerations. Using this unique separation technique, specular and diffuse reflection coefficients were deduced for various terrain types. The separation technique developed in this paper can be readily applied to existing height-gain data if the system geometry is known     

High-resolution radar imagery of the Mirage III aircraft

High-resolution radar imagery has attracted increasing interest in recent years. As more radars are endowed with a high-resolution capability, target classification will become a regular system function. In order to classify an aircraft using radar, one must have an understanding of how the radar imagery relates to the physical aircraft. This paper illustrates the more important radar backscattering features on a typical fighter aircraft. Radar backscatter from an aircraft can occur through a variety of mechanisms. Although direct specular and diffractive mechanisms usually account for the majority of the scattering, indirect phenomena such as cavity scattering and creeping wave scattering are significant. This investigation finds that scattering from engine cavities is a particularly important radar backscatter mechanism for a fighter aircraft. Radar data of an actual Mirage aircraft is collected from a target turntable facility. This data is processed to obtain high-resolution range profiles (HRRP) and inverse synthetic aperture radar (ISAR) images, which indicate the prominent radar scatterers on the aircraft. The imagery is qualitatively examined, and its suitability for target classification is discussed     

空间色噪声背景下双基地多输入多输出雷达低仰角估计方法

针对多径效应的影响,该文提出一种空间色噪声背景下双基地多输入多输出(MIMO)雷达低仰角估计方法。首先对双基地MIMO雷达中低仰角目标的多径环境进行建模,同时考虑发射和接收端的镜面反射信号,并用空间色噪声模拟漫反射。然后利用协方差矩阵求差方法消除未知色噪声的影响,在发射端和接收端进行空间平滑对多径信号解相干,即进行空间差分平滑处理。最后利用酉变换旋转不变技术(ESPRIT)算法估计目标的发射角(DOD)和接收角(DOA)。该文指出特殊情况下空间差分平滑协方差矩阵缺秩的问题,并提出一种修正的空间差分平滑方法。该算法对阵元数要求不高,适用于未知噪声背景及低信噪比环境,并且解决DOD与DOA联合估计的角度兼并问题。仿真实验表明了所提算法的有效性。     

An adaptive-window-width short-time Fourier transform forvisualization of radar target substructure resonances

A short-time Fourier transform with an adaptive-window-width is used to analyze the transient response of radar targets. The described algorithm allows the isolation and identification of substructure resonances as well as localized specular reflections and slowly building global resonances     

多径条件下米波频分MIMO雷达波束性能及优化方法

针对传统米波雷达低仰角下波瓣分裂和盲区问题,该文提出一种频率分集子孔径MIMO雷达,构建了该体制下多径特性定量分析的理论框架,推导了镜面反射和扰动多径模型及其联合发射-接收方向图增益闭合表达式;提出了多径抑制区概念及其边界条件,定义了描述低空波束覆盖性能的低可观测率定量评价指标;根据边界条件的解集优化了波束覆盖性能。理论分析和仿真结果表明由于充分利用了频率分集产生的距离依赖波束,该体制雷达相对传统MIMO相控阵雷达具有更优的低空波束覆盖性能,减小了米波雷达波瓣分裂和探测盲区。     

Représentation ponctuelle de la contribution de la frontière d’ombre d’un objectif radar et son introduction dans le modèle des points brillants

In order to study the scattering of a monochromatic electromagnetic wave by a complex target (generally a plane), radar specialists usually replace the target by a collection of independent point contributors. The model obtained is called a discrete scatterers model because the majority of the scatterers are represented by specular points of reflection on the surface of the target. The possibility of optical perception of specular points and the apparent simplicity of the method make it very attractive, and this explains its success. The litterature about this technique tends to assume that it is known and understood, and therefore rarely explains the basics. The result is sometimes an impression of empiricism and a tendancy to mistake the optical problem for the easily ignored electromagnetic one which often leads to results so bad that they cannot be used even for the simplest of targets. In this article, the author explains the concept of point contributor in detail and show that the shadow boundaries on the surface of a target can also be represented by imaginary specular points and thus can be easily included in the model. The author studies the effect of imaginary points on the radar cross section of the targets, and illustrates the results obtained by applying the method to a few simple objects.     

Error probability of M-ary FSK with differential phasedetection in satellite mobile channel

Formulas are derived for the error probability of M-ary frequency shift keying (FSK) with differential phase detection in a satellite mobile channel. The received signal in this channel is composed of a specular signal, a diffuse signal, and white Gaussian noise; hence, the composite signal is fading and has a Rician envelope. The error probability is shown to depend on the following system parameters: (1) the signal-to-noise ratio; (2) the ratio of powers in the specular and diffuse signal components; (3) the normalized frequency deviation; (4) the normalized Doppler frequency; (5) the maximum normalized Doppler frequency; (6) the correlation function of the diffuse component, which depends on the normalized Doppler frequency and the type of the antenna; (7) the number of symbols; and (8) the normalized time delay between the specular and diffuse component (t _d/T) where 1/T is the symbol rate. Except for T_d/T, all normalized parameters are the ratios of the parameter value and symbol rate. The Doppler frequency depends on the velocity of the vehicle and the carrier frequency. The error probability is computed as a function of the various parameters. The bit error probability is plotted as a function of signal-to-noise ratio per bit and other system parameters