海洋环境对雷达海杂波后向散射特性影响分析

为分析海洋环境对雷达海杂波后向散射特性的影响,建立了一种基于修正复合模型方法的雷达海杂波后向散射关系模型。雷达入射余角较大时,主要散射形式为镜面散射;入射余角较小时,主要散射形式为Bragg散射。考虑了逆顺风条件下后向散射系数的差异性,改进了原有模型Bragg散射的方向海谱部分,增加了风向因子。利用模型对不同入射角条件下海洋环境因素与后向散射系数的关系进行了仿真计算。计算结果表明,当海面作为雷达波的反射面时,雷达后向散射特性十分复杂,风速、风向、海浪、降水、海面油污等海洋环境因素都会对其产生影响。其中,风速和有效波高对海面后向散射的影响最大,风向次之,降水再次之,而海面油污的影响最小。      

海杂波统计特性分析

分析了海杂波背景下的目标检测的困难,研究了后向散射系数在海杂波的各个散射区中的性质,列举分析了几种常用的海杂波后向散射系数理论模型,重点分析了海杂波幅度特性和海杂波相关特性,不但有助于设计和实现雷达滤波器,而且有助于提高抑制杂波的能力以及保证雷达应有的探测性能。     

天波超视距雷达海杂波特性研究

本文首先根据高频电磁波与海面相互作用产生Bragg谐振散射的特性分析了一阶海杂波的产生机理,得到了一定入射余角条件下一阶海杂波的多普勒频移特性,然后对天波雷达体制下海杂波的平均后向散射系数建模,仿真分析了雷达频率、海面风速、风波角、海浪有向波高谱关于海面风向的扩展程度等参数对一阶海杂波后向散射的影响,得出各参数对一阶海杂波后向散射的影响规律。     

海杂波幅度分布模型的研究

为改善雷达检测目标的能力,基于对海杂波幅度特性的分析,采用瑞利分布、韦布尔分布、对数正态分布、K分布进行仿真,并与实测数据对比,分析了四种分布方式的拟合特点。由结果可知,雷达处于低分辨率高擦地角时,适用于瑞利分布;当雷达处于高分辨率低擦地角时,适用于其余三种分布,其中正态分布拟合的效果较好。由四种分布的参数拟合图知,K分布参数可以作为特征参量,更好地将主、次目标单元分离开来,为提高雷达检测能力提供依据。     

小麦水稻后向电磁散射建模研究σ°与入射角的关系

本文从小麦水稻的散射机理出发，把来自小麦水稻的后向散射分为三部分：植被层的贡献、土壤的贡献以及植被层与土壤的相互作用贡献。植被层选用云雾模型，土壤直接运用Ｋｉｒｈｈｏｆｆ散射模式，这样建立了小麦水稻电磁散射的半经验模型。当植被衰减较大或入射角较大时，主要贡献是植被层的贡献，该项趋近于常数γ模型。而在小角度下，主要是土壤的贡献，它随入射角增大衰减很快。这样，模型退化成修正常数γ模型（Ｇａｕｓｓ衰减加上常数γ）。模型与ｘ波段实测数据有较好的吻合度。     

波导环境下雷达后向散射系数研究

海上大气波导会显著改变雷达电磁波的传播性能,反应到雷达图像上表现为强烈的海杂渡回波信息。为了探究大气波导的影响因素,采用改进的GIT模型仿真方法模拟出波导背景下不同风速对雷达后向散射系数的影响,并且利用谱估计技术计算出掠射角随距离的变化。通过仿真结果分析,风因子对雷达后向散射系数影响显著,仿真结果对进一步利用海杂波反演大气渡导及提高舰载雷达探测性能具有重要指导意义。     

浅析海杂波抑制方法

海杂波是影响对海雷达工作性能的一个重要因素。检测和跟踪目标之前抑制海杂波是非常必要的。通过对海杂波和舰船目标的幅度特征、谱特征以及相关特征的分析，针对强海杂波环境下，目标检测的典型问题，从雷达工作模式、雷达信号处理两个方面探讨了抑制海杂波的几种途径。     

基于电磁模型的宽带雷达海杂波信号建模与分析

该文针对时变海洋面雷达回波信号模拟问题,建立了一种包含电磁散射机理与雷达波形调制特征的海杂波雷达回波信号模型。该模型首先建立一组具有时变特征的海面几何样本,通过对改进双尺度面元模型的加速处理,实现各时刻海面散射数据的高效模拟,并通过与测试数据的对比证实了电磁计算方法的准确性,然后采用子脉冲形式建立宽带回波信号模型,并以各面元散射数据代替其复幅度从而完成雷达回波信号建模。通过仿真验证了模型的合理性与高效性,对海杂波数据的统计分析展示了脉冲压缩处理对杂波的抑制效果。该海杂波模型既考虑了海洋的复杂散射机理与运动特性,又具有一般宽带信号的形式,因此可同时为海洋散射现象的解释和信号处理算法的分析提供完备数据源。     

海杂波的分数布朗运动模型及其应用

海杂波常常严重地限制了雷达目标检测能力。通常是采用统计方法研究海杂波的特性，随着新理论、新技术的出现，不断尝试更好的方法研究海杂波。基于分形理论，利用实测的小擦地角海面雷达回波数据，比较了海杂波和分数布朗运动（FBM）的性质，得出海杂波与分数布朗运动有相似的增量统计特性。在此基础上，利用基于FBM模型的分维数提取方法对两组海杂波含目标信号进行处理，与利用脉冲回波相干处理以及变换法的分形处理方法相比，具有较好的效果。     

海杂波背景下的目标检测分析与仿真

本文采用蒙特卡罗方法对于海杂波背景下的雷达信号检测做出了理论分析和仿真模拟,针对不同的海杂波背景环境给出了不同检测概率下的目标信号最小幅度需求以及无偏差判决的基本条件,给出了不同检测门限值下的检测概率和目标信号关系的比较。     

A new model for sea clutter

First-order (small roughness amplitude) scattering theory is applied to obtain sea clutter cross sections in terms of mean-squared height spectrum of the sea surface. The results are in remarkably good agreement with observations for vertical polarization atP-, L-, C-, andX-bands. Modification of the calculation to take into account the larger scale structure of the sea surface yields reasonable agreement for horizontal polarization atP- andL-bands but is less successful for the cross-polarized and horizontal cross sections atC- andX-bands.     

An experimental study of a sea clutter model

A model for the radar cross section (RCS) of the sea has been developed in parallel efforts by scientists in both the United States and the Soviet Union, which is based upon the concept of a composite surface, i.e., one in which a slightly rough surface in the sense of Rice is superimposed on a larger swell structure. For angles off the normal, the model predicts the variation of the RCS with frequency, polarization, and incident angle of the illumination and further predicts an upper bound (saturation value) of the RCS with increasing roughness. The model has been collated with data collected by the Naval Research Laboratory four-frequency radar system in sea states ranging from 0 to 7. The results of the comparison have shown that the upper bound for the RCS exists and is closely approached in windspeeds in excess of 5 m/s. In addition, the data have confirmed the variation of RCS with frequency (UHF to X-band), grazing angle, and with polarization (H, V), provided that the "tilting" of the scattering surface by swell is taken into account in the region of shallow grazing angles.     

双站高频地波雷达一阶海杂波技术研究

随着雷达技术的发展,双(多)基地组网成为主流发展方向,因为相对于单基地而言,双(多)基地在抗打击方面,具有单基地没有的优势。而在对抗电子干扰的问题上,双(多)基地更是具有得天独厚的优势。而一阶海杂波作为海面本身特有的属性,无论是在海洋参数反演,还是在海面动目标识别过程中都具有非常重要的意义。     

Evaporation duct effects on sea clutter

Existing sea clutter models are in general agreement on the trends and magnitudes of sea reflectivity at low (1°-10°) grazing angles. However, at extremely low grazing angles (<1°), models, theory, and measurements show considerable differences. The effects of the oceanic evaporation duct on grazing angle are investigated. Significant changes in grazing angle due to the evaporation duct are found and the illumination of the sea surface by the radar is shown to extend well beyond the standard (4/3 earth) radar horizon range. A series of sea clutter model comparisons shows that much of the difference between models can be attributed to evaporation duct effects     

海杂波特性分析方法研究和比较

在分析了一阶、多阶海杂波产生机理的基础上,从三个方面对现有的海杂波特性分析方法进行了总结和比较,并从统计特性和混沌特性的角度对海杂波特性作了进一步的研究,为全面研究海杂波特性及雷达系统仿真提供了理论依据。     

Small-target detection in sea clutter

Sea clutter in marine surveillance radar makes the task of detecting small targets a very challenging problem. In this paper, a set of three signal processing techniques designed to suppress unwanted sea clutter radar echo and achieve target detection with no prior knowledge of the ocean and environmental conditions is presented. These include signal averaging, time-frequency representation, and morphological filtering. Datasets from real marine radar operating in staring mode are used to illustrate the performance of the new approaches.     

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.