Modified GIT model for predicting wind-speed behavior of low-grazing-angle radar sea clutter

A modified GIT model for describing the variational trend of mean clutter reflectivity as a function of wind speed is proposed. It uses two slope adjustment factors and two critical wind-speed factors to define and adjust the increasing slope of reflectivity with respect to wind speed. In addition, it uses a constant factor to compensate the overall amplitude of clutter reflectivity. The performance of the modified GIT model has been verified on the basis of the L-band low-grazing-angle radar sea clutter data. The results are in good agreement with the experimental data, indicating that the model is more effective in predicting the wind-speed behavior of clutter reflectivity than the conventional GIT model, especially for lower and higher wind speeds. We believe that the proposed model can provide deeper insights into the relationship between radar sea clutter reflectivity and sea state conditions.

Reflectivity Model of Low Grazing Angle Radar Sea Clutter

The commonly used reflectivity models of radar sea clutter are summarized. Among these models, the adjusted Barton model and the adjusted Morchin model are compared. From the analysis result, the γ-p reflectivity model is presented for low grazing angle radar sea clutter by the adjustment of the original Barton reflectivity model. The model takes into account radar frequency, grazing angle, sea condition, and polarization property. The influences of these factors on the proposed model are analyzed. The model absorbs the merits from commonly used reflectivity models for sea clutter. It introduces several researchers' opinions, and extends them. And it accounts for the reflectivity at arbitrary radar frequency from VHF to X-band, arbitrary low grazing angle, arbitrary sea condition and different polarization property. One of the main results is the proposed γ-p reflectivity model can reflect the influence of polarization on sea clutter reflectivity to some extent. The proposed γ-p reflectivity model of low-angle radar-sea clutter is validated by comparing the simulated and statistically experimental data.

Effect of Changes in Sea-Surface State on Statistical Characteristics of Sea Clutter with X-Band Radar

We have made observations of X-band radar sea clutter from the sea surface and sea-surface state in the Uraga Suido Traffic Route, which is used by ships entering and leaving Tokyo Bay, and the nearby Daini Kaiho Sea Fortress. We estimated the distributions of reflected amplitudes due to sea clutter using models that assume Weibull, Log-Weibull, Log-normal, and K-distributions. We then compared the results of estimating these distributions with sea-surface state data to investigate the effects of changes in the sea-surface state on the statistical characteristics of sea clutter. As a result, we showed that observed sub-ranges not containing a target conformed better to the Weibull distribution regardless of Significant Wave Height (SWH). Further, sub-ranges conforming to the Log-Weibull or Log-normal distribution in areas contained a target when the SWH was large, and as SWH decreases, sub-ranges conforming to a Log-normal. We also showed that for observed sub-ranges not containing a target, the shape parameter, c, of both Weibull and Log-Weibull distribution correlated with SWH. The correlation between wave period and shape parameters of Weibull and Log-Weibull distribution showed a weak correlation.

First order sea clutter cross section for bistatic shipborne HFSWR

This paper studies the development on the first order sea clutter cross section for bistatic high frequency surface wave radar (HFSWR). Based on the received first order electric field expression, a closed-form of cross sections is derived to account for the case of receiving antenna array being mounted on the shipborne platform. The uniform linear motion and sway motion components are assumed to be responsible for the observed differences in comparison with the bistatic fixed antenna case. Correspondingly, simulations are conducted to study the sea clutter spectral characteristics for these two cases versus different system parameters and sea state conditions. It is shown numerically that the forward motion component will spread the Bragg lines severely and the influence triggered by the sway motion can be explained as the Bessel function modulation of the ordinary sea clutter spectra. The obtained results have important implications in the application of shipborne HFSWR technology to ocean remote sensing and target detection.

A statistical distribution of quad-pol X-band sea clutter time series acquired at a grazing angle

Although the complex Wishart distribution has been widely used to analyze the statistic properties of quad-pol SAR spatial data, the applicability of this complex distribution to the time series of sea clutter is rarely discussed.The measured data of the quad-pol X-band marine radar demonstrate that the time series of the sea echoes are also satisfied the circular Gaussian distributions if the low intensity signals, which are mainly dominated by a radar noise, in the shadow regions of the large-scale waves are removed. On the basis of this fact, the probability density functions（PDFs） of the intensity as well as the phase, the real and the imaginary parts of the sea echoes obtained by the marine radar have been derived, and the theoretical models are all expressed in closed forms. In order to validate the theoretical results, the PDFs are compared with the experimental data collected by the Mc Master IPIX radar. And the comparisons show that the PDF models are in good agreement with the experimental data.

Effective Sea Clutter Spectrum Extraction Method for HFSWR in Adverse Conditions

An effective approach in solving the sea clutter spectrum extraction problem is studied in the paper.Different from the conventional signal to noise ratio（SNR）method based on Doppler frequency or range domain information,a method is developed to characterize the differences between the sea echo and those interferences are by signal to interference plus noise ratio（SINR）which jointly utilizing the range,Doppler frequency and azimuth domain information.Furthermore,these differences can be adaptable to adverse conditions by forming the necessary boundaries and constraints in searching of the maximum SINR,which greatly promotes the extraction of sea clutter spectrum.The real high frequency surface wave radar（HFSWR）data demonstrate that the proposed method is less influenced by those interferences and can effectively extract the sea clutter spectrum even under the adverse conditions.Furthermore,it has been shown as an effective method for ship detection and sea state remote sensing of HFSWR.

大掠射角对海雷达导引头实测回波特性分析

大掠射角下,对海雷达导引头观测到的海杂波强度激增,舰船目标检测困难。本文结合全极化雷达导引头挂飞实测数据,分析了回波幅度和相位特性。首先,采用典型分布对回波幅度分布进行拟合,并利用拟合优度对拟合效果作出评估;然后,分析了平均相位变化量。结果表明:在大掠射角条件下,雷达导引头各极化通道海杂波幅度服从K分布;海杂波与舰船回波幅度在同极化通道服从K分布,在交叉极化通道服从对数正态分布;交叉极化通道回波信杂比高于同极化通道;海杂波与舰船回波相位平均变化量小于海杂波。

基于雷达目标特征可分性的一维特征选择方法

海杂波背景下的海上小目标是海洋雷达探测的重难点。针对特征空间内海杂波与小目标特征可分性问题,提出了量化特征之间可分性的度量标准——重叠系数。通过开展对海探测试验获取的2~5级海况实测数据,分别提取时域特征相对平均幅度(Relative Average Amplitude,RAA)、相对峰值峰高(Relative Peak Height,RPH)、时域熵值均值(Time domain Entropy Mean,TEM),频域特征相对多普勒峰高(Relative Doppler Peak Height,RDPH)、相对多普勒向量熵(Relative Vector Entropy,RVE)、频域熵值二阶矩(Second moment of Frequency domain Entropy,SOFE),计算出重叠系数。通过特征检测器进行检测性能对比,低海况下,相对平均幅度、相对峰值峰高、时域熵值均值、相对多普勒峰高、频域熵值二阶矩特征之间重叠系数均在0.3以下,对应特征检测器的检测概率均在85%以上;高海况下其特征之间重叠系数均在0.7以上,对应特征检测器的检测概率均在50%以下。相对多普勒向量熵在4种海况下可分性较小,其对应的特征检测器性能较差。结果验证了重叠系数在一维特征选择的应用可行性,为多特征融合目标检测提供了一定支持。

对数正态纹理距离相关性辅助的海杂波背景雷达目标检测方法

传统的海杂波背景雷达目标自适应检测器通常假设杂波纹理在距离维上独立同分布,忽略了纹理在距离维的相关性信息。为了改善纹理距离相关海杂波环境下雷达目标自适应检测性能,该文首先将复合高斯海杂波的纹理分量建模为对数正态随机变量,然后基于广义似然比检验提出一种基于均匀对数正态纹理的广义似然比检测器。提出的雷达目标自适应检测器融合了纹理的先验分布知识及其在距离维的相关性信息。仿真和所用实测数据表明,与已有检测方法相比,所提方法对纹理距离相关海杂波背景下的雷达目标具有更高的检测概率。

基于深度学习的多特征融合海面目标检测方法

该文考虑了海杂波环境下的雷达目标检测问题,提出了一种基于深度学习的海面目标检测器。该检测器通过融合从不同数据源中提取的多种互补性特征以增加目标和杂波的差异性,从而提升对海面目标的检测性能。具体来说,该检测器首先利用两个特征提取分支分别从距离像和距离多普勒谱图中提取多层次快时间特征和距离特征;然后,设计局部-全局特征提取结构从特征的慢时间维度或多普勒维度提取序列关联性;接着,提出基于自适应卷积权重学习的特征融合模块,实现快慢时间特征和距离多普勒特征的高效融合;最后,对多层次特征进行融合、上采样和非线性映射获得检测结果。基于两个公开雷达数据集上的实验验证了所提检测器的检测性能。

基于改进DeeplabV 3+的HFSWR电离层杂波及海杂波自动识别

针对高频地波雷达(HFSWR)回波谱中背景噪声复杂、杂波占比较小且电离层杂波形态位置各异,难以自动识别的问题,以DeeplabV3+深度学习算法为基础架构并加以改进,提出一种HFSWR电离层杂波及海杂波自动识别方法。选用轻量级MobileNetV2作为主干特征网络,加入通道注意力机制模块SENet,实现对杂波标签的侧重学习,优化训练集中各类标签的损失权重;采用模型预训练迁移法对网络进行预训练,解决样本空间过小的问题。实测数据集上的实验结果表明,本方法可以实现HFSWR电离层杂波及海杂波的自动识别。相比原DeeplabV3+算法,杂波识别结果更为准确和精细,海杂波识别结果的平均交并比(mIoU)和准确率(ACC)分别提升2.9%和5.1%;电离层杂波识别结果的mIoU和ACC分别提升3.0%和4.9%。

基于相对多普勒峰高特征的OS-CFAR改进方法

在传统有序统计类恒虚警的基础上,提出了1种基于相对多普勒峰高特征的改进有序统计类恒虚警检测方法。该检测算法结合相对多普勒峰高(RDPH)特征和有序统计类(OS-CFAR)检测算法的优势,对雷达回波数据的相对多普勒峰高特征进行计算,通过排序选取参考单元的特征估计,得到检测门限,并通过仿真与实测数据测试对比该算法与其他传统恒虚警算法在不同背景下的检测性能,验证该算法的优势。结果表明:相较于传统均值类、有序统计类恒虚警检测算法,基于相对多普勒峰高特征的改进OS-CFAR检测算法在实测海雷达数据的高海况场景下能够达到更好的检测概率。

基于SOCP理论的船舶导航雷达海杂波抑制算法研究

为了有效降低海杂波对船舶导航雷达工作的影响,提出了一种基于二阶锥规划(SOCP)理论的杂波抑制算法。针对传统的实系数有限冲激响应(FIR)数字滤波器组无法保证通带群延时(小数)精度的问题,通过将初始优化问题转化为对偶问题进行求解,利用SOCP理论的分布式计算优势,稳定有效地求取其局部最优点,同时用重构的海杂波样本反复训练理论模型。通过仿真实验证明SOCP理论可以更好地重构信号检测模型,大幅抑制海杂波的影响,提高船舶导航雷达的目标检测能力。

复杂海况下对海搜索雷达波形参数设计研究

针对雷达波形参数对海杂波环境下的雷达作用距离影响很大的问题,基于经典的海杂波归一化散射系统模型,建立海杂波背景下的雷达方程,结合典型探测高度分析雷达波形参数带宽、脉冲重复周期对典型海面目标探测能力的影响,给出不同场景下的雷达波形参数设计方案,可为对海探测波形参数设计提供依据。

基于Tri-feature训练的目标与海杂波鉴别算法

针对海杂波背景下末制导雷达容易出现错误检测的问题,开展海杂波抑制和鉴别研究。采用基于Tri-feature训练的目标鉴别分类算法,以目标幅度、峰值持续范围和起伏率作为特征量,核函数选择径向基函数(radial basis function,RBF)。RBF非线性映射能力强,在高维空间中可以更好地表达数据之间的关系,然后进行支撑向量机(support vector machine,SVM)目标鉴别分类器设计和实验数据验证。经公开的实测数据验证,所提算法准确率达到97%以上。通过与传统的模板匹配识别方法进行对比,基于Tri-feature训练的目标鉴别分类算法有更高的鉴别准确率,证明了所提方法的有效性和先进性。

基于舰载雷达的海杂波特性分析与仿真

舰载雷达在海面作战中具有重要的作用,对舰载雷达所处的海面环境进行分析,及时将舰载雷达所受到的海杂波的特性进行分析和仿真,能够提高舰载雷达探测目标的准确性。论文首先对海杂波的后向散射特性进行了分析和阐述,之后对于海杂波的后向散射特性进行了建模与仿真。为舰载雷达的海杂波特性分析提供了新的思路。

Application of pre-whitened-constrained-MUSIC in ship-borne radar

In ship-borne radar, because of the influence of interference factors such as the correlation of background array noise and the coherence of targets and so on, the performance of high-resolution algorithms such as MUSIC is degraded. In this document by pre-whitening of background array color noise, de-correlation of coherent targets, compensation of amplitude-phase mismatch, pre-whitened-constrained-MUSIC algorithm in ship-borne radar effectively resolutes ship target and first-order sea echo. Furthermore, the algorithm performance is compared with other algorithms, result shows that pre-whitened-constrained-MUSIC can be applied effectively in high-resolution processing in ship-borne radar.

雷达恒虚警目标检测处理技术综述

恒虚警处理技术作为雷达自动检测系统中非常重要的一种目标自动检测方法而被广泛深入研究。首先介绍了几种高斯与非高斯背景下经典的恒虚警检测技术,分析不同应用背景的恒虚警检测器的选取;然后介绍了与背景分布无关的非参量恒虚警算法以及变换域恒虚警处理、多维信息联合、多传感器分布式检测、极化恒虚警等现代目标检测恒虚警处理技术;最后,对未来雷达恒虚警检测技术进行展望,为恒虚警技术的创新与应用提供参考方向。

基于改进ALO-RBF的高频地波雷达海杂波预测模型

高频地波雷达是海上动目标检测的重要手段,其中海杂波是影响海面目标检测性能的主要因素。为了提高海杂波的预测精度进而有效抑制海杂波,本文提出了一种基于改进蚁狮算法(Ant Lion Optimizer,ALO)优化RBF神经网络的海杂波预测模型(MGPALO-RBF,Multiple elites dynamic guidance Ant Lion Optimizer based on Gaussian difference variation-based learning with Perturbation factor-radial basis function)。由于标准蚁狮算法具有易陷入局部最优且收敛速度慢的缺点,本文在蚂蚁进行随机行走的过程中加入扰动因子以增加种群的活跃性和多样性,并提出多个精英动态引导机制,强化算法前期的探索能力和后期的开发能力,同时对种群中较差蚁狮进行高斯差分变异以提高算法的收敛速度。仿真结果表明:改进的蚁狮算法在对比算法中具有更高的收敛精度和收敛速度,MGPALO-RBF模型具有更好的海杂波预测性能。

基于实测数据的海杂波与海面小目标特征分析

目标特性是雷达目标检测识别等精细化处理的基础。设计检测器主要是设计1个检测统计量,使之在有无目标时有尽可能大的差别。经典的检测主要用幅度特性、相关性等。利用X波段雷达2~5级海况下航道浮标实测数据,分别对比分析海况连续变化下海杂波和海面小目标的时间相关性、空间相关性、相对平均幅度(Relative Average Amplitude,RAA)、相对多普勒峰高(Relative Doppler Peak Height,RDPH)和相对多普勒向量熵(Relative Vector Entropy,RVE)5种特征的变化情况。大量实测数据验证表明,随着海况等级增加,海杂波与海面小目标的时空强相关数值逐渐变小:2~5级海况下,RAA具有较好的可区分性;2~3级海况下,RDPH据有较好的可区分性,4~5级海况下区分效果不理想;5级海况下,RVE的具有较好的可分效果。结论对于海杂波背景下雷达目标特征检测方法优化设计具有重要意义。