合成孔径雷达图像的恒虚警率目标检测

目的　对合成孔径雷达 (SAR)图像实施恒虚警率 (CFAR)目标检测 .方法　利用 K-Gamma和Weibull分布的杂波模型分别对海面和陆地的人造目标实施检测 ;同时 ,对不同杂波背景下 CFAR检测方法进行比较 .结果与结论　通过检测结果的比较 ,证实了 K-Gamma分布和 Weibull分布分别适合于海面和陆地杂波背景下的目标检测 ;在非均匀杂波背景中 ,有序统计量 (OS)较单元平均 (CA)方法具有优越性     

Performance of the adaptive generalised matched subspace constant false alarm rate detector in non-Gaussian noise: an experimental analysis

The authors deal with the performance analysis of an adaptive version of the generalised matched subspace detector (GMSD) in compound-Gaussian clutter with unknown covariance matrix. The original GMSD was proposed to detect subspace signals in compound-Gaussian noise with known covariance matrix and ensures the constant false alarm rate (CFAR) property. In real situations, this assumption is unrealistic, which means that the covariance matrix must be estimated from training data. The authors use a robust estimate of the covariance matrix called the fixed-point estimate, recently proposed in the literature. The performance of the obtained adaptive detector, in terms of CFAR behaviour and probability of detection, is evaluated in the presence of real sea clutter data, collected by the McMaster IPIX radar.     

Non-coherent radar CFAR detection based on goodness-of-fit tests

This paper considers the problem of constant false alarm rate (CFAR) detection of radar targets using multiple observations. In the Gaussian clutter scenario, the structure of the optimum (uniformly most powerful) CFAR detector is rather simple, but when the clutter is heavy-tailed, that is non-Gaussian distributed, the derivation of the optimal detector becomes infeasible. For this latter relevant case, a new CFAR algorithm is porposed based on goodness-of-fit (GoF) tests. The performance of the proposed detector is numerically investigated through Monte Carlo simulations assuming heavy-tailed Weibull and Lognormal distributed clutter. Numerical results shown that, in heavy-tailed clutter and also when several interfering targets exist, the proposed detector outperforms the conventional CFAR detector based on binary integration. Performance is also tested processing real sea clutter data collected by a non-coherent navigation radar     

Constant false-alarm rate algorithm based on test cell information

A new constant false-alarm rate (CFAR) detection algorithm, designated as switching CFAR (S-CFAR), is proposed and analysed. The S-CFAR algorithm selects CFAR reference samples using the magnitude of the sample in the cell under test, which is an information that has not been exploited in any other existing CFAR detectors. S-CFAR closed-form analysis is presented, and comparisons with other representative CFAR algorithms are given. An S-CFAR detector can be tuned such that it has a small CFAR loss when operating on a homogeneous background while achieving improved robustness in the presence of interfering targets and clutter power transition. The S-CFAR detector is also simple to design and implement since no sample ordering is required.     

Signal-to-noise ratio analysis to estimate ocean wave heights from X-band marine radar image time series

This work analyses the structure of the different contributions to the image spectrum derived by the three-dimensional Fourier decomposition of sea clutter time series measured by ordinary X-band marine radars. The goal of this investigation is to derive a method to estimate the significant wave height of the ocean wave fields imaged by the radar. The proposed method is an extension of a technique developed for the analysis of ocean wave fields by using synthetic aperture radar systems. The basic idea behind this method is that the significant wave height is linearly dependent on the square root of the signal-to-noise ratio, where the signal is assumed as the radar analysis estimation of the wave spectral energy and the noise is computed as the energy due to the sea surface roughness, which is closely related to the speckle of the radar image. The proposed method to estimate wave heights is validated using data sets of sea clutter images measured by a marine radar and significant wave heights derived from measurements taken by a buoy used as reference sensor.     

Extraction of mixed-order multicomponent ship target signals from broadened sea clutter in bistatic shipborne surface wave radar

A dynamic geometry model was built to describe the Doppler-broadening characteristics of the first-order Bragg lines for bistatic shipborne surface wave radar. They are time-varying because the Doppler frequency shifts of sea echoes are simultaneously modulated by the velocity components projected from the unavoidably different motions of both platforms, which is more complex than its counterpart in the monostatic mode. The geometrical relation is used to obtain the received signal model: strong first-order sea clutter interferences and submerged ship targets with constant and non-constant speeds are considered as mixed-order multicomponent polynomial-phase signals (mc-PPSs) and both second-order sea clutter continuum and atmospheric noise as additive noise. Then, a scheme based on the product high-order ambiguity function is proposed to extract the targets; it is a recursive procedure in which the first-order sea clutter is removed by an existing time-space cascaded filtering method. Monte Carlo simulations show the validity and efficiency of the proposed scheme.     

基于多背景杂波分布模型的自适应CFAR检测

针对现有的CFAR(Constant False Alarm Rate,恒虚警)算法采用全局建模,在待检测的所有区城采用同种背景杂波分布模型,导致使用的模型在不适应区域失配,使CFAR检测性能下降的现象,本文提出一种基于多背景杂波分布模型的自适应CFAR检测算法.该方法根据背景区域的不同统计特性即统计方差和均值比来判断...     

Ionospheric clutter mitigation using one-dimensional or two-dimensional wavelet processing

Ionospheric clutter mitigation is an important issue for high-frequency surface wave radar (HFSWR) signal processing. Clutter results from a sky wave propagation mode, which is backscattered by ionospheric ionisation irregularities. The random behaviour and the high strength of clutter signals can strongly limit the HFSWR detection capabilities. Here, an ionospheric clutter mitigation processing using wavelets is described. This new approach is founded on the ability of wavelets to separate signals having different variation scales or different directions of variations. The results obtained on real clutter signals with simulated targets are reported. Using the proposed method, one can expect, at mid-latitude, an improvement of the target-toclutter ratio of 20?30 dB.     

非平稳环境下主动声呐检测器研究

针对在水下存在多途、混响及噪声边缘等非平稳背景条件下主动声呐检测器的检测性能,给出了一种变异指数的恒虚警率(Variability Index Constant False Alarm Rate,VI-CFAR)检测器。VI-CFAR结合了单元平均恒虚警率、最大选择恒虚警率和最小选择恒虚警率的检测算法,它在均匀平稳环境和非平稳环境下都具有较强的自适应性。理论分析和仿真结果表明,该检测器在均匀平稳背景下的检测性能与单元平均恒虚警率检测器相似,在多途、混响等干扰背景条件下具有较强的抗干扰能力,在噪声边缘背景下有较好的虚警概率控制能力且运算量小,是一种稳健的检测器。     

Application of the radon transform to detect small-targets in sea clutter

The authors present a novel and heuristic approach for the detection of low radar cross-section targets in high-resolution sea clutter. The proposed technique is based on the application of the Radon transform to range?time matrices formed by column-wise storage of consecutive range profiles. The objective of this paper is 2-fold: to analyse the effect of the transform on real high-resolution sea clutter and to describe a detection scheme based on the insight obtained. The proposed technique emulates the behaviour of traditional motion target detection algorithms without the need for reliable Doppler information. It also constitutes a powerful non-coherent integration strategy of the target?s energy along its specific path on the range?time plot. The performance of the detection technique has been tested against real high-resolution sea clutter data, acquired at the south coast of Spain with an in-house developed continuous wave linear frequency modulated millimetre-wave radar system. Monte Carlo simulations show a significant improvement over the conventional cell averaging constant false alarm rate schemes.     

低频脉冲信号的频域恒虚警检测

为提高低频背景噪声中弱声呐脉冲信号的检测能力,给出了一种频域恒虚警检测方法。该方法针对低频背景噪声平稳性较差、起伏较大的特点,将频域中峰值点或极值点认为是疑似脉冲信号,通过对疑似点能量与历史背景进行比对的方式完成脉冲信号的检测判决,并且给出了相应的检验统计量获取方法、背景噪声估计方法和恒虚警检测门限的计算方法。仿真分析和实际数据处理结果表明,频域恒虚警检测方法对单频脉冲、单频-线性调频组合脉冲等包含窄带成分的弱声呐脉冲信号有非常好的检测性能。     

Performance analysis of ordered-statistic greatest of-constant false alarm rate with binary integration for M-sweeps

The performance of the ordered-statistic greatest of (OSGO) constant false alarm rate (CFAR) scheme with binary integration for M non-coherent sweeps in Weibull background was investigated for homogeneous and non-homogeneous backgrounds, with an assumption of known shape parameter. This kind of processing is based on the fact that the clutter can be segmented in regions in many real radar scenarios where a timevarying two-parameter distribution function family can be fitted, but the clutter power may vary locally inside the region. Under the assumption of known shape parameter, the authors examined the changes of the false alarm rate and detection probability of the OSGO-CFAR with binary integration when the shape parameter differs from the nominal one, and compared them to those of the OSGO-CFAR with single pulse processing. The authors have derived analytic expressions of the detection probability and false alarm rate during clutter power transitions for the OSGO-CFAR with binary integration in Weibull background. It is shown that the OSGO-CFAR with binary integration can not only improve the detection performance significantly, but it also control the rise of the false alarm rate at clutter edges more effectively compared to the OSGO-CFAR with single pulse processing. Moreover, it exhibits a good immunity to the variation of the shape parameter.     

高频雷达海杂波混沌特性的实验研究

利用高频地波雷达实测数据 ,从实验角度应用动力学方法对高频海杂波的动力特性作出分析 ,首次得到了高频海杂波呈现混沌特性的结论。这一结论对高频雷达目标探测和海态遥感以及海洋气象的研究都具有重要意义。     

海面波浪起伏对声传播的影响

位于南海某海域同一传播路径上,在2004年和2005年分别进行的两次声传播实验,两次实验中的设备、过程和方法都相同,水文变化也不大,但实验得到的传播损失相差却很大。通过对实验数据的分析表明,两次实验的传播损失差异是由于海面波浪起伏引起的。利用第一次实验数据,考虑海面波浪起伏后反演得到的海底吸收系数可以较好地解释另一次的声传播损失。因此,可以以为浅海海面波浪起伏对声传播的影响很大,在进行水下声传播规律的研究或地声参数反演研究时,应当充分考虑海面波浪起伏的影响。     

Granular flow in the marginal ice zone

The region of sea ice near the edge of the sea ice pack is known as the marginal ice zone (MIZ), and its dynamics are complicated by ocean wave interaction with the ice cover, strong gradients in the atmosphere and ocean and variations in sea ice rheology. This paper focuses on the role of sea ice rheology in determining the dynamics of the MIZ. Here, sea ice is treated as a granular material with a composite rheology describing collisional ice floe interaction and plastic interaction. The collisional component of sea ice rheology depends upon the granular temperature, a measure of the kinetic energy of flow fluctuations. A simplified model of the MIZ is introduced consisting of the along and across momentum balance of the sea ice and the balance equation of fluctuation kinetic energy. The steady solution of these equations is found to leading order using elementary methods. This reveals a concentrated region of rapid ice flow parallel to the ice edge, which is in accordance with field observations, and previously called the ice jet. Previous explanations of the ice jet relied upon the existence of ocean currents beneath the ice cover. We show that an ice jet results as a natural consequence of the granular nature of sea ice.     

基于小波分解的 K-分布 SAR 图像舰船检测

舰船目标检测是合成孔径雷达海洋应用的一个重要组成部分. 通过对合成孔径雷达图像中舰船目标和海杂波背景的结构差异特点进行分析,提出了一种利用小波分解技术和 K-分布海杂波模型的恒虚警率舰船目标检测方法,并对实际 SIR-C C 波段 SAR 图像进行了实验. 实验结果表明,该方法能够在复杂相干斑和海杂波背景中大幅增强舰船目标,并且有效保证了检测结果的准确性.     

CuNiBe合金超声波探伤衰减严重的原因及解决措施

分析了用于汽轮发电机转子槽楔的CuNiBe合金的组织,研究了探伤过程中出现林状杂波较多、一次底波与二次底波高度相差较大及无底波现象的原因。通过在合金中加入微量钴元素、增加变形量的手段来改变材料的组织。改进后的CuNiBe合金探伤时,不再出现林状杂波和底波消失的现象。     

Infrared radiance and solar glint at the ocean-sky horizon

An analytic model is developed for the mean and clutter infrared radiance emitted from the ocean surface near the horizon and in the presence of solar glint. The model is based on the identification of a characteristic facet dimension over which the ocean surface is essentially flat. Fluctuations in the facet orientation generated by the water wave motion are modeled by a parameterized wave height power spectral density that provides the two orthogonal wave slope variances. The mean and root-meansquare facet radiances are calculated with Gaussian probability-density functions for the wave slopes. One can determine the number of facets within the field of view of a single detector by estimating the exposed ocean area and dividing by the facet area. This estimation takes into account shadowing effects of the swell wave, the swell wavelength, and the transverse detector field of view. The number of exposed facets together with the central-limit theorem permits computation of the radiance clutter as a function of look-down angle below the horizon. Vertical radiance profiles, parameterized by the azimuthal offset from the solar position, are calculated over a sensor look-down angle range of ±50 mrad about the horizon. The results of this analysis are compared with infrared radiance measurements of the ocean surface near the horizon and in the presence of solar glint. Agreement between the measured and calculated values of the mean and clutter radiances is good.     

水下无人航行器自主检测方法研究

自主检测技术是实现水下无人航行器(Underwater Unmanned Vehicle,UUV)智能化的关键技术,是无人航行器能够自主执行水下预警、目标跟踪等任务的前提。针对当前基于均值类和有序统计类恒虚惊(Constant False Alarm Rate,CFAR)技术的自主检测方法在背景起伏严重、多目标情况下,背景噪声统计特性估计不准确、自主检测性能下降的问题,文章提出了一种基于方位-时间二维参考窗联合有序截断平均算法的自主检测方法。首先,该方法设计了一种方位-时间二维参考窗,解决了一维参考窗检测参考样本过少、噪声统计量估计不准的问题;其次,采用有序截断平均算法估计背景噪声统计量,对起伏背景进行均衡;最后,利用背景噪声均值和方差构造恒虚警检测器,采用检测前跟踪技术,实现起伏背景下、多目标自动检测与跟踪。湖上试验结果表明,在水下无人航行器的自噪声干扰下,该方法对多目标依然具有较好的自主检测效果。     

脉冲多普勒引信杂波启动特性的计算机仿真

在下视工作过程中会时有发生地、海杂波,将会对引信低空的正常运作产生较大的负面影响。该文结合脉冲多普勒引信的特征,采用计算机仿真技术,构建相应的理论模型,多角度地分析影响杂波信号强度的因素,进而提出基于引信距离-多普勒分辨单元方法下所展开的杂波信号强度分析途径。通过实例计算机仿真研究,从两个不同情况对计算机仿真技术的内容进行了一定程度的验证。