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基于相参X-波段海洋雷达的海表轮廓测量研究 总被引：4，自引：2，他引：2
X-波段海洋雷达测量所得海面散射单元的多普勒信息与散射单元的雷达视向速度密切相关。首先,基于符号多普勒估计方法,对X-波段雷达海面回波的多普勒频移信息进行了估计;在此基础上,应用各分辨单元回波的多普勒频移信息,建立了海浪表面轮廓的反演算法。该算法中,同时考虑了雷达入射角、方位角和雷达空间分辨率等因素对反演结果的影响。通过将反演结果与浮标测量数据相比较,发现雷达空间分辨率起到了类似低通滤波的作用,该作用对短重力波谱影响显著。同时,还应用加拿大麦克马斯特大学的IPIX雷达数据对海表轮廓进行了反演,并将反演所得有效波高、海浪周期与现场测量数据进行了比较,反演结果与现场测量结果吻合较好。 相似文献
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海洋微波散射模型相比于以经验统计建立的地球物理模式函数具有不受特定微波频率限制的优势。组合布拉格散射模型和几何光学模型形成了复合雷达后向散射模型。利用南海北部气象浮标2014年海面风速风向实测值作为散射模型输入，分别比较了复合雷达后向散射模型与RADARSAT-2卫星C波段SAR、HY-2A卫星Ku波段微波散射计的海面后向散射系数，偏差分别为(?0.22±1.88) dB (SAR)、(0.33±2.71) dB (散射计VV极化）和(?1.35±2.88) dB (散射计HH极化)；以美国浮标数据中心(NDBC)浮标2011年10月1日至2014年9月30日共3年的海面风速、风向实测值作为散射模型输入，分别比较了复合雷达后向散射模型与Jason-2、HY-2A卫星Ku波段高度计海面后向散射系数，偏差分别为(1.01±1.15) dB和(1.12±1.29) dB。中等入射角和垂直入射下的卫星传感器后向散射系数观测值与复合雷达后向散射模型模拟值比较，具有不同的偏差，但具有相同的海面风速检验精度，均方根误差小于1.71 m/s。结果表明，复合雷达后向散射模型可模拟计算星载SAR、散射计和高度计观测条件下的海面雷达后向散射系数，且与CMOD5、NSCAT-2、高度计业务化海面风速反演的地球物理模式函数的计算结果具有一致性；复合雷达后向散射模型可用于微波遥感器的定标与检验、海面雷达后向散射的模拟。 相似文献
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针对海杂波严重制约雷达目标探测性能的问题,本文提出了一种基于复相关相位斜率特征的海面弱小目标检测方法。本文通过研究海杂波复数域下的时间自相关特性,发现复相关系数相位信息呈线性分布,由此提出了一种新颖的统计特征:复相关相位斜率。研究表明,复相关相位斜率特征可显著提高雷达数据的信杂比。经过不同极化方式下的海杂波数据验证表明,本文提出的目标检测方法性能优于传统基于分形特征的Hurst指数检测器,使用本文的方法可以有效识别海面弱小目标。 相似文献
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《海洋湖沼通报》2019,(6)
对于SAR风浪图像而言,速度聚束调制常导致图像中散射面元沿方位向产生位置交叠,从而引起强烈非线性特征,难于仿真;另外,SAR图像强度是由雷达飞行过程中多次观测所得的散射回波相干叠加获得,然而,传统SAR海浪图像仿真方法中并未考虑该相干叠加过程。为了解决第一个问题,文中首先应用线性滤波法对海浪运动引起的速度聚束效应进行仿真,统计方位向各像素位置处发生交叠的散射面元数目,并将各散射面元回波进行非相干叠加。针对第二个问题,本文则根据海面微波散射场时间序列的相位差近似满足高斯分布这一事实,将雷达沿方位向飞行过程中不同时刻所得的散射场引入满足高斯分布的随机相位,进而再将方位向不同时刻散射场进行相干叠加。最后通过将仿真所得SAR图像的强度分布与经验分布函数进行比较,初步检验了本文仿真方法的可行性,同时还分别分析了风速、风向、速度聚束调制等因素对仿真SAR图像的影响。 相似文献
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为了解各向异性随机粗糙海面的微波双站散射机制及其特性，本文利用解析近似的积分方程模型以及一种改进的半经验海浪谱模型实现了对各向异性随机粗糙海面的全极化微波散射仿真模拟，并与卫星观测数据、经验的地球物理模式函数及已有的解析近似散射模型仿真结果进行了对比，验证了仿真结果的可行性和准确性。利用该模型分析了入射波频率、入射角、极化方式、海面风速及风向等参数对各向异性海面双站散射的影响。模拟结果表明，在不同的入射角、散射角及方位角等观测几何条件下，海面不同波段的双站散射表现出不同的空间散射特性，且对风速、风向等海面动力学参数表现出不同的敏感性，以L波段为例，海面向后半球双站散射在各个极化方式下都对风速较为敏感，而在同极化方式下，其对风向的响应在中低风速和高风速条件下相反，整体而言，低风速下海面双站散射对风向更为敏感。这表明对于海面动力参数的反演，双站散射可以提供比传统单站雷达后向散射更丰富的物理信息。本文探讨了各向异性海面微波双站散射特性，为基于主动式及分布式微波传感器的海洋动力参数遥感反演提供了理论分析基础。 相似文献
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海面电磁回波频谱宽度与海浪波高密切相关，可应用频谱宽度进行海浪有效波高反演。本文应用线性滤波法仿真出了海表散射面元在雷达视向上的投影速度，建立了回波谱宽模型，分析了雷达空间分辨率、回波时间序列长度及海洋环境参数等因素对频谱宽度的影响，同时还针对如何在实际观测过程中选择回波时间序列长度、观测方位角等参数进行了讨论。最后还将理论结果与CSIR-X波段雷达实测数据谱宽估计结果进行了比较。结果表明，剔除雷达噪声以及频率泄露的影响后，基于高斯分布标准偏差的谱宽估计方法所得结果与理论结果吻合很好，这从而证明了理论结果的可靠性。本文所得结果对海浪有效波高反演具有一定参考价值。 相似文献
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随着雷达成像技术和高分辨率光栅显示技术的发展和应用,基于船载雷达图像的船只检测成为可能.海上船只检测的主要困难之一是雷达图像中包含固有的海面背景杂波.传统的雷达船只检测方法,如恒虚警率法(CFAR),以杂波分布模型为基础,计算待检测窗口中的信号统计分布来确定自适应阈值,取得了一些成果.但是,当海面背景杂波和船只目标的回波强度在同一数量级,甚至船只目标淹没在海面背景杂波中时,就难以确定一个有效的阈值将船只目标从雷达图像中提取出来.在分析海面背景杂波和船只目标的相关差异性基础上,提出了一种基于船载雷达序列图像的海上船只快速检测方法.该方法首先对相邻两幅图像进行互相关性分析,在两幅图像中的同一位置提取一定尺寸的移动窗口,计算其互相关函数值,窗口移动一个步长,重复操作直至遍布整幅图像,形成一幅由灰度图像互相关函数值组成的相关图像.然后使用概率神经网络模型(PNN模型)来估计相关图像背景杂波的灰度概率密度分布函数(PDF),应用CFAR技术,使用二分法求解一个区分船只和背景噪声的自适应整体阈值,并根据阈值将相关图像二值化,其中大于阈值的像元作为候选的船只目标信息,小于阈值的像元则为海面背景杂波.最后使用连通性8-邻域准则统计各个候选船只目标区域的像元数,并与预先定义的最小船只目标像元数进行比较,偏小的候选船只目标区域作为虚警去除,保留下来的候选船只目标区域即为船只检测结果.研究显示,如果图像序列中没有船只目标信息,则三维相关图像比较平整.相反,如果图像序列中含有船只目标信息,则三维相关图像上有峰值被检测出,通过测量峰值的高度,就能判断存在可能的船只目标.运用X波段船载雷达序列图像对本文提出的海上船只检测方法进行了测试.测试结果表明,该检测方法具有很好的船只检测效果,得到的船只检测结果与目视判别的结果一致.而且该检测算法原理简单,计算速度快,易于实时处理,具有广阔的应用前景. 相似文献
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船用X波段导航雷达凹波形成的海杂波图像中包含丰富的海浪、海表层流信息.借鉴合成孔径雷达(SAR)估计有效波高的方法,假设有效波高与雷达回波强度信噪比的平方根成线性关系,可由X波段雷达图像估计得到海浪的有效波高.用此方法主要分析小麦岛海域实验数据,结果显示,直流滤波后计算的信噪比估计的有效波高比不进行直流滤波结果符合得好;而按波浪浮标测得有效波高数据的高低,分两段分别进行线性拟合获取校准系数,估测的有效波高更加准确. 相似文献
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Ship navigation through ice-infested waters is a problem of deep concern to the oil exploration industry of Northern countries. Conventional marine radars do not perform satisfactorily in detecting small targets such as small pieces of iceberg. This paper reports a new method for detection in an ocean environment. The approach is based on the recent observation that sea clutter, radar echoes from the sea surface, can be modeled as a nonlinear deterministic dynamical system which can be used as an alternative to the conventional stochastic process. Based on this model, detection in sea clutter is considered as dynamical system classification instead of statistical hypothesis testing. Two dynamical detection methods are proposed. The first one uses a dynamical invariant called the attractor dimension to distinguish a target from a pure clutter process. The second approach tries to detect the existence of a target by observing the “difference” of the motion of the target and the clutter process. To show the validity of the idea of dynamical detection in sea clutter, real sea clutter, and target data were used in this study 相似文献
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The accurate prediction of non-linear sea states represents a great challenge, with a number of applications in oceanography, marine engineering, security of people and marine transportation, etc. In this paper, we report on the development of two efficient deterministic prediction models for 2D irregular wave-fields. These models are based on the exploitation of wave elevation time series given by one or more probes and on the use of two different numerical models for the wave-fields simulation. Two effective data assimilation processes are developed to improve the wave-field estimates obtained from the study of one or several probe signals, so that we obtain proper initial conditions for the forecast. The assimilation schemes have been validated on the reconstruction of model-generated observations and accurate predictions of the corresponding synthetic wave-fields evolution have been obtained. 相似文献
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海杂波微弱目标分形检测 总被引：1，自引：1，他引：0
The target on the sea surface is complex and difficult to detect due to the interference of backscattered returns from the sea surface illuminated by the radar pulse. Detrended fluctuation analysis （DFA） has been used successfully to extract the time-domain Hurst exponent of sea-clutter series. Since the frequency of the sea clutter mainly concentrates around Doppler center so that we consider to extract frequency-do- main fractal characterization and then detect a weak target within sea clutter by using the difference of frequency-domain fractal characterization. The generalized detrended fluctuation analysis （GDFA） is more flexible than traditional DFA owing to its smoothing action for the clutters. In this paper, we apply the GDFA to evaluate the generalized Hurst exponent of sea-clutter series in the frequency domain. The difference of generalized Hurst exponents between different sea-clutter range bins would be used to determine whether the target exists. Moreover, some simulations with the real IPIX radar data have also been demonstrated in order to suooort this conclusion. 相似文献
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Several important statistical properties of the HF sea echo and its Doppler power spectrum, which are useful in optimizing the design of radar oceanographic experiments, are established. First- and second-order theories show that the echo signal (e.g., the voltage) should be Gaussian; this is confirmed with experimental surface-wave data i) by comparison of the normalized standard deviation of the power spectrum at a given frequency with its predicted value of unity, and ii) by cumulative distribution plots of measured spectral amplitudes on Rayleigh probability charts. The normalized standard deviation of the dominant absolute peak amplitudes of the power spectrum (which wander slightly in frequency) are shown from experimental data to besim 0.7 for the first-order peaks andsim 0.5 for the second-order peaks. The autocorrelation coefficient of the power spectra is derived from measured data and interpreted in terms of the spectral peak widths; from this information, the correlation time (or time between independent power spectrum samples) iS shown to besim 25-50 s for radar frequencies above 7 MHz. All of these statistical quantities are observed to be independent of sea state, scattering cell size, and relatively independent of radar operating frequency. These quantities are then used to establish the statistical error (and confidence interval) for radar remote sensing of sea state, and it is shown, for example, that 14 power spectral samples result in a sample average whose rms error about the true mean is 1.0 dB. 相似文献
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Evaporation duct is an abnormal refractive phenomenon in the marine atmosphere boundary layer. It has been generally accepted that the evaporation duct prominently affects the performance of the electronic equipment over the sea because of its wide distribution and frequent occurrence. It has become a research focus of the navies all over the world. At present, the diagnostic models of the evaporation duct are all based on the Monin-Obukhov similarity theory, with only differences in the flux and character scale calculations in the surface layer. These models are applicable to the stationary and uniform open sea areas without considering the alongshore effect.This paper introduces the nonlinear factor av and the gust wind item wg into the Babin model, and thus extends the evaporation duct diagnostic model to the offshore area under extremely low wind speed. In addition, an evaporation duct prediction model is designed and coupled with the fifth generation mesoscale model(MM5).The tower observational data and radar data at the Pingtan island of Fujian Province on May 25–26, 2002 were used to validate the forecast results. The outputs of the prediction model agree with the observations from 0 to 48 h. The relative error of the predicted evaporation duct height is 19.3% and the prediction results are consistent with the radar detection. 相似文献
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近海海流受多种动力过程及岸线岛屿的作用呈现空间和时间尺度上的复杂变化,而地波雷达由于其探测面积广、时间分辨率高的特点成为研究这些变化的有效手段。本文利用舟山海域多年高频地波雷达资料,通过潮流调和分析、低通滤波和相关性分析对该海域海流潮周期、极端事件、季节、年际尺度的动力过程进行了解译。研究表明,舟山海域属于正规半日潮,潮流运动形式以顺时针旋转流为主,流速大小在空间上为东北方向较大,往西南方向逐渐减小,并在近岸处得到增强。余流的年际变化并不显著,但存在着明显的季节变化,例如冬季为南向流,流速减小,空间分布上近岸较外海大,而夏季与之反向,为北向流,流速较大,空间分布较为均匀。进一步分析了风与余流之间的相关性,在大风期间,风与余流的速度相关系数在0.48～0.90之间,方向相关系数在0.55～0.68之间。极端事件发生时,速度、方向的相关系数分别高达0.92与0.91。总体而言,通过分析高频地波雷达数据能够较好地反映舟山海域海流的时空特征,为海洋灾害监测和污染物、藻华的输运研究提供依据。 相似文献