Analysis of sea spikes in radar sea clutter data

In this paper three sets of high-resolution, coherent, and polarimetric radar sea clutter data are analyzed and compared with radar sea clutter models. The nature of the data allows a thorough analysis of the power, polarization and velocity of the sea clutter. It is shown that these quantities, especially the velocity, are good measures of many physical properties of the ocean surface. Furthermore, it is shown that these physical properties match well with the sea clutter models. Sea clutter is found to consist of two components, a diffuse background, characterized by low values of backscattered power, HH/VV polarization ratio and Doppler velocity, and a number of spiking events, which possess higher power, polarization ratio and velocity. The background is reasonably well modeled by tilt-modulated Bragg scattering, whereas the spikes may be associated with the scattering on steepened and/or breaking waves. Moreover, it is shown that the influence of microbreakers has to be taken into account to explain the relatively high polarization ratio. A breaking wave origin for the spikes is supported in two ways. First, by a detailed analysis of the temporal behavior of individual spike backscatter properties, and second, by a statistical analysis of the entire population of spikes.     

多径效应及其对二次警戒雷达的干扰影响

在航空交通管制(ATC)方面,二次警戒雷达(SSR)较之一次雷达有许多优点,且有较好的性能/价格比。由于二次雷达在航管方面的应用愈来愈多,二次雷达的一些系统问题也就表现得较为突出了。本文讨论了多径和互扰的一些问题,并提出了相应的解决方法。     

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.     

Target decomposition theorems in radar scattering

By converting the coherent scattering matrix into a target vector, the concept of a coherency matrix may be introduced for characterising statistical scattering problems involving polarised waves. This technique is compared with the more conventional Mueller matrix formalism and a unique decomposition theorem developed for modelling dynamic scattering problems.     

Surface-based radar imaging of sea ice

The paper examines the use of a surface-based marine radar for imaging the surface features of sea ice in full ice cover. Two aspects of the problem are considered: 1) selection of radar parameters which maximize the effectiveness of the radar for ice imaging, and 2) evaluation of image processing (display) techniques that effectively convey to an operator the information contained in the radar returns. Both aspects of the study are supported by data collected at a radar site on Baffin Island, Canada. The paper also briefly describes the characteristics of first-year ice, multiyear ice, and icebergs, which are pertinent to the understanding of the radar ice-imaging problem. Based on the results presented on radar parameter evaluation, it is recommended that: 1) the radar resolution should be as high as possible; 2) the antenna should be installed as high as possible; 3) the radar should receive both like- and cross-polarized returns; 4) two radars, operating at widely separate frequencies, should be used. Based on the results of the display work, it is recommended that: 1) the display should use a scan technology that affords the required number of intensity levels; 2) median filtering should be used to reduce the effects of spike noise, if present; 3) normalization should be used to remove the range-dependence of radar returns; 4) selective edge enhancement be employed to maximize significant image detail; 5) to fully utilize the intensity levels available in the display, the histogram of the image should be modified, taking into account the visual response of the operator; 6) color can be used to accommodate the display of multi-parameter images, such as those arising from the use of like. and cross-polarization; 7) Features 3), 4), and 5) may be integrated into a modular image processing system.     

高频地波雷达海洋回波处理中的噪声研究

从理论上研究了经快速富氏变换（FFT）处理后的海洋表面回波噪声统计特性发生的变化。这种变化影响使用多信号分类（MUSIC）算法探测海洋表面流的到达角。使用参数模型谱估计和两次FFT方法，对浙江舟山朱家尖测得的海洋表面回波数据进行了处理，分析和比较，两次FFT方法获得的谱比参数模型估计谱信噪比差，证明了本文理论研究结果的正确。     

On radar pulse scattering from ionized media

Some preliminary work relating to the pulse radar return from ionized media, such as fireballs resulting from nuclear explosions and the wakes of high-speed reentry vehicles, is reported. In all cases the objective is to retrieve the envelope of the backscattered signal correctly related in time to the transmitted pulse.     

A GTD-based parametric model for radar scattering

This paper presents a new approach to scattering center extraction based on a scattering model derived from the geometrical theory of diffraction (GTD). For stepped frequency measurements at high frequencies, the model is better matched to the physical scattering process than the damped exponential model and conventional Fourier analysis. In addition to determining downrange distance, energy, and polarization, the GTD-based model extracts frequency dependent scattering information, allowing partial identification of scattering center geometry. We derive expressions for the Cramer-Rao bound of this model; using these expressions, we analyze the behavior of the new model as a function of scatterer separation, bandwidth, number of data points, and noise level. Additionally, a maximum likelihood algorithm is developed for estimation of the model parameters. We present estimation results using data measured on a compact range to validate the proposed modeling procedure     

Bistatic radar scattering by a chaff cloud

The bistatic radar scattering cross section of a chaff cloud is investigated in the ground-based system for arbitrarily polarized transmitters and receivers. The chaff cloud considered consists of a large number of identical thin conducting wires whose thickness is very small compared to their length and to the wavelength. Numerical results for bistatic cross sections for the cases of orientations uniform in azimuth and Gaussian in elevation, and also for uniformly random orientation in both azimuth and in elevation are presented in the form of three-dimensional graphs, for a few typical examples     

A time-frequency analysis method for radar scattering

A time-frequency analysis method to study electromagnetic scattering is presented and demonstrated using canonical objects. The time-frequency analysis method utilizes the Bargmann transform to formulate the signal representation in phase space. The use of the Bargmann transform leads to an attractive parametric signal representation in terms of complex polynomials, and elliptical filters can be constructed to crop or extract selected areas of the phase plane. The signal representation and filtering operations are demonstrated using scattering responses from spheres and thin wires, and the prominent scattering features are identified and extracted     

Control of radar scattering by reactive loading

A method for obtaining a desired radar scattering pattern by reactively loading a conducting body is given. The theory uses the concept of characteristic modes of a loaded body. Any desired real current can be resonated by reactive loads to make it the dominant mode current of that body. If no other mode is near resonance, the radar scattering pattern becomes nearly the same as the radiation pattern of the resonated current. A quality factorQis defined as a measure of the broadband behavior of a scatterer. Procedures for computing the real currents having minimumQand maximum gain-quality ratio are given. A pattern synthesis procedure is developed for obtaining the real current whose radiation field pattern is the least mean-square approximation to a desired field pattern. Numerical examples are given for each procedure discussed.     

真空罐内雷达目标散射特性测量方法的研究

为了在真空条件下对等离子体云团的雷达波散射特性进行快速测量和分析,系统采用了真空罐模拟目标飞行时的高空大气环境,使用传统的线性调频测量体制和单天线方案,在近距离实现了关于等离子体云团的单站RCS测量,测量精度较以往的双天线方案有所提高。     

Numerical simulation of low-grazing-angle ocean microwavebackscatter and its relation to sea spikes

This paper presents the results of numerically simulating microwave backscatter from a deep-water breaking wave profile. Enhanced microwave backscatter from the crests of breaking waves has been hypothesized as the source of bright short-lived microwave radar echoes that are observed at low-grazing angles (LGAs). The characteristics of these “sea spikes” are distinctly different from the Bragg-scatter echoes that dominate measurements made at moderate grazing angles. Of particular interest is the high contrast that sea spikes present against ocean background backscatter when observed with horizontally polarized transmit/receive configurations [horizontal (HH) versus vertical (VV)]. This HH/VV contrast disparity has been attributed to polarization-selective cancellation of the direct reflection from the wave crest by the surface reflection. This hypothesis is reinforced first by showing evidence that VV polarization is suppressed in the intensity range that would normally be populated by the brightest scatterers. Histograms of unaveraged Doppler-centroid measurements show further that the depleted VV backscatter population is responding to scatterers that are moving much more slowly than the HH scatterers. The Doppler-centroid histograms provide a sharper delination between the two scattering populations than do the unconditionally averaged Doppler spectra that are more commonly reported. Finally, our numerical simulations show evidence of an interference mechanism that selectively suppresses VV backscatter. In our simulations, the polarization selectivity comes from the phase dependence of the backscatter from the wave crest. A Brewster phenomenon at the surface reflection point is not necessary     

Development of a ground-based radar for scattering measurements

A ground-based C-band scatterometer system has been constructed at the Multimedia University, Malaysia. This is an inexpensive FM-CW radar that was efficiently constructed from a combination of commercially available components and in-house fabricated circuitry. The system has full polarimetric capability for determining the complete backscattering matrix of a natural target. It will be used to conduct in-situ backscatter measurements on Earth terrain, such as vegetation fields, forests, and soil surfaces. This paper presents the system design and the evaluation results of the scatterometer system. The system was tested at a football field. A metal sphere was used as the calibration target. The backscattering matrices of an 8" trihedral corner reflector and of a 4" /spl times/ 8" dihedral corner reflector were measured. The dihedral was rotated at different angles to provide different sets of polarimetric data. The results were compared with the theoretical values to verify the effectiveness of the calibration technique. The external calibration and internal calibration procedures, as well as the approach used in measuring the relative phase response, are discussed.     

Absolute phase of the radar target scattering matrix

By carefully considering the voltage equation for a polarimetric radar, it can be seen that the absolute phase of the target scattering matrix provides additional useful information about the target. This fact has apparently been overlooked in the past.<>     

雷达定标卫星光学散射特性研究

对主体为铝球用于雷达定标的一批卫星进行了地基光学观测,验证了其光度变化和光谱特性简单,易于开展光度和光谱特性影响因素分析。实验室对铝球的仿真测量也证明了铝球具有各向同性好、反射特性和光谱特性平稳等特点。研究团队基于测量结果构建了铝制球体卫星的光度计算模型,与实测结果的对比分析表明,利用铝制球体的材料特性和外形特征可最大程度的简化卫星光度计算模型,也证明了实测方法和光度计算模型构造方法的正确性,使得卫星光度可实时保精计算,可应用于天基和地基光电探测设备的动态能量定标和高速、变速运动状态下的探测能力标定。     

雷达目标的散射中心建模研究

雷达目标总散射场可近似为若干散射中心贡献的叠加,而每一个散射中心都对应着特定的电磁散射机理,这些特定散射机理的散射场可表示成输入为雷达参数（频率、极化、视向角）和目标参数（几何、材料）的参数化模型.散射中心参数化模型在雷达回波实时模拟、半实物仿真、雷达目标识别等领域得到了广泛的关注.文中总结了雷达散射中心模型的发展历程,包括散射中心数学模型和散射中心参数提取方法,以及散射中心建模的难点问题和未来的研究方向.期望该文可为从事该方面研究的科研人员提供一些参考.     

高频雷达海杂波的多重分形建模方法研究

将多重分形理论引入高频雷达海杂波建模,提出了一种新的高频雷达海杂波的时域多重分形模型。对比分析了实测数据海杂波、分数布朗运动(FBM)模型和多重分形模型的质量指数函数和奇异指数,结果表明:该多重分形模型与实测数据具有相似的多重分形性。此外,通过对韦布尔分布、对数正态分布和瑞利分布三种最常用海杂波的概率密度函数的比较分析,并利用修正的柯尔莫哥洛夫-斯米尔洛夫(K-S)统计检验,得出了高频雷达海杂波的多重分形模型具有先验的统计特性的结论,从而进一步证明了该多重分形模型的合理性和有效性。