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1.
This paper proposes the retrieval method of ocean wave spectrum for airborne radar observations at small incidence angles, which is slightly modified from the method developed by Hauser. Firstly, it makes use of integration method to estimate total mean square slope instead of fitting method, which aims to reduce the affects of fluctuations superposed on normalized radar cross-section by integration. Secondly, for eliminating the noise spectrum contained in signal spectrum, the method considers the signal spectrum in certain look direction without any long wave components as the assumed noise spectrum, which would be subtracted from signal spectrum in any look direction for linear wave spectrum retrieval. Estimated ν from the integration method are lower than the one from fitting method and have a standard deviation of 0.004 between them approximately. The assumed noise spectrum energy almost has no big variations along with the wave number and is slightly lower to the high wave number part of signal spectrum in any look direction, which follows that the assumption makes sense. The retrieved directional spectra are compared with the buoy records in terms of peak wavelength, peak direction and the significant wave height. Comparisons show that the retrieved peak wavelength and significant wave height are slightly higher than the buoy records but don’t differs significantly (error less than 10%). For peak direction, the swell waves in first case basically propagate in the wind direction 6 hours ago and the wind-generated waves in second case also propagate in the wind direction, but the 180? ambiguity remains. Results show that the modified method can carry out the retrieval of directional wave spectrum. 相似文献
2.
声学多普勒流速剖面仪(ADCP)是对海洋内波监测的有效手段,但受到仪器本身和复杂的海洋环境噪声等影响,走航式ADCP记录的海流数据存在大量噪声,且混有流速异常值。为了进一步提高海洋内孤立波的提取精度与准确性,本文针对走航式ADCP海流数据特点引入IGG3方法的权函数因子,设计了一种抗差Vondrak滤波器,并与快速傅里叶变换、小波分析和滑动平均3种传统滤波方法进行对比,以验证抗差Vondrak滤波方法的有效性与优越性。研究结果表明,抗差Vondrak滤波方法不仅可以有效地滤除流速噪声,还可以自适应剔除海流观测数据中的异常值,由其提取出的内孤立波准确且各层水平流速清晰。因此,与传统滤波方法相比,抗差Vondrak滤波方法在内孤立波提取方面具有一定的优越性。 相似文献
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The Goda's method of separating the frequency spectrum of the unidirectional incident and reflected waves is improved. The proposed method can be applied to the separation of oblique incident and reflected waves and the two wave gauges can be arranged in an arbitrary angle in front of a structure. When the projected distance of the two probes on the incident wave direction is the multiple ofthe half length of the incident waves, the singular problem will emerge by using the method. It is advised that when the projected distance of the two measured points on the incident wave direction is 0.05～0.45 times the wave length of peak frequency wave, good results can be obtained. The simulated resultant waves are separated by the method of numerical simulation and the separated wave spectra are basically corresponding to the target spectra input. The wave trains calculated by the separated incident and reflected wave frequency spectrum are approximated to the input wave trains and the reflected coefficient can be derived correctly. Therefore, the method proposed in this paper is reliable. 相似文献
4.
椒盐噪声是常见的图像噪声,典型的图像平滑算法不能区分海岸带高分辨率遥感图像中的噪声点和信号点,常造成图像平滑后海岸线等细节损失。提出先识别噪声点再进行去噪的新方法,通过统计关联参数用双阈值识别噪声,然后用中心权值为零的模板平滑噪声点。实验表明,该方法在滤除椒盐噪声的同时,较好地保持了海岸线等细节。 相似文献
5.
—In this paper,the second-order perturbation method in frequency domain is used to calculateRAO and spectra of motion and mooring line tension of a turret-moored tanker in ballast condition.Thecalculated results are compared with corresponding experiment results.In the experiment the wave head-ing is 180°,and the wave spectra is the P-M spectrum and white noise spectrum.In the theoretical calcu-lations,the damping coefficient of slow oscillation of the tanker is determined on the basis of the dampingobtained from a test of irregular waves where the mooring system is replaced by a nonlinear spring withnonlinear stiffness similar to that of the mooring system.From the comparison between theoretical calcula-tions and experimental results,it can be found that the theoretical results obtained by the second-orderperturbation method in frequency domain are in good agreement with the experimental results,indicatingthat the damping coefficient of slow oscillation of the tanker required in frequency domain calcu 相似文献
6.
合成孔径雷达是海洋内波研究中最重要的工具之一。雷达图像中的斑点噪声会严重降低图像的质量,这一问题在处理和分析信号较弱的二模态内波信号和上升型内波信号时极为明显。合成孔径雷达图像中的海洋内孤立波的信号具有明显的尺度性和方向性。同时,curvelet变换作为一种同时具备尺度分辨率和方向分辨率的数学变换,能够对一幅雷达图像在不同尺度、不同方向和不同位置上进行分析。本文给出了一个基于curvelet变换的合成孔径雷达海洋内孤立波图像的斑点噪声抑制方法。该方法可简述为：(1)对一幅合成孔径雷达海洋内孤立波图像进行curvelet变换,获得curvelet系数;(2)分别仅仅保留一个尺度的系数,将其它尺度的系数置为零,利用处理之后的系数分别重建图像,得到仅仅用一个尺度的系数重建的图像;(3)分别计算上一步中得到的图像的均方差,根据波浪理论,图像的方差代表能量,方差越大则能量越大,以此可以确定内波信息集中的尺度;(4)在每个尺度下,分别计算每个方向的curvelet系数矩阵的平均值,以此确定内孤立波信号集中的方向;(5)在上两步工作的基础上,仅仅保留内波信号集中的尺度和方向的系数,而将其它尺度和方向的系数置为0,得到一幅提取主波信息的图像;(6)将上一步得到的提取主波信息的图像加回到原始图像中,从而达到增强波浪信息并抑制斑点噪声的目的。大量的实验验证表明,该方法不仅能有效地压制斑点噪声,而且能有效地增强波浪信号。 相似文献
7.
Recovery of surface-wave time series from pressure gage data is a time-consuming process and is not customarily carried out. Such information is, however, useful particularly in real-time for warning of freak waves or waves of unusual characteristics. Two simple numerical filters are developed here to serve such purpose. The first method is a linear filter with a built-in window to suppress high-frequency noise. The second method recovers the surface wave by computing the local surface curvature. These filters are very simple and can be programmed into a microprocessor to be integrated into field instrument packages.Both filters have been tested satisfactorily against conventional linear filters using simulated wave data and wave data collected in intermediate water depth. Neither filter requires pre-filtering of noise from raw data, which is commonly required to recover surface-wave information from sub-surface pressure data. 相似文献
8.
Zhu Liangsheng Sui Shifeng
Associate Professor South China Sea Institute of Oceanology Chinese Academy of Science Guangzhou Professor South China Sea Institute of Oceanology Chinese Academy of Science Guangzhou 《中国海洋工程》1997,(3)
Some researches have been made in this aspect.In the method by Walton Jr.(1992),incidentwaves are supposed to be the overlapping result of M component waves with different frequencies whichmay take different directions,the direction of incident waves should be available in advance,but in fact thedirection of incident waves is not available.In our study,incident waves are supposed to be composed ofM overlapping component waves with different frequencies,and different frequencies have different direc-tions.Based on the irregular wave reflection theory,the calculation formulas of wave direction,complexamplitude of incident waves,and complex amplitude of reflected waves in surface which are composed ofcomponent waves are derived by means of discrete Fourier transform.Then,the frequency spectra of inci-dent waves and reflected waves and the reflection coefficient of waves with corresponding frequencies areobtained.Verification of the method and the calculation results from in-situ measured data indicate thatt 相似文献
9.
A technique is developed to separate the incident and reflected waves propagating on a known current in a laboratory wave–current flume by analyzing wave records measured at two or more locations using a least squares method. It can be applied to both regular and irregular waves. To examine its performance, numerical tests are made for waves propagating on quiescent or flowing water. In some cases, to represent the signal noise and measurement error, white noise is superimposed on the numerically generated wave signal. For all the cases, good agreement is observed between target and estimation. 相似文献
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本文首先对合成孔径雷达（SAR）海浪成像中的3种调制（倾斜调制、流体力学调制与速度聚束调制）的影响进行了对比分析,结果显示:速度聚束调制对SAR图像的影响最为显著。另外,由于SAR图像中固有相干斑噪声的存在,较低波数范围的噪声难以滤除或抑制,利用经典MPI方法反演海浪谱会造成低波数范围谱值偏大。基于此,本文借鉴经典MPI海浪谱反演算法,建立了基于速度聚束调制的海浪方位向斜率谱和有效波高的反演算法。通过将经典MPI方法、同极化调制法及本文算法等3种海浪反演方法所得有效波高与浮标数据进行比较,结果显示:本文方法反演得到的海浪有效波高与浮标数据获得的有效波高之间的均方误差为0.79 m,为3种方法中最小。 相似文献
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In order to prevent the generation of spurious free sub- and superharmonics of random waves in a laboratory channel, the control signal for the wave board has to be derived according to a higher-order wave theory. An expression for this control signal has been derived with the perturbation method of multiple scales. It is much less complex and requires less computation time than the expressions obtained from the full second-order theory. The new method for second-order subharmonics was verified experimentally for waves with bichromatic and continuous first-order spectra. The data were analysed with the complex-harmonic principal-component analysis to reduce the influence of noise. 相似文献
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A process of synthetic aperture radar imaging of ocean surface waves is considered on the basis of the two-scale model of microwave scattering by a disturbed sea surface. Analytical expressions are obtained to relate characteristics of a large-scale wave image, averaged over an ensemble of realizations of the small-scale ripple, with the wave, radar, and viewing scheme as parameters. It is shown that the wave image would be defocused as an image of a target moving in the along-track direction with a speed equal to a half of the wave phase speed projection on the line of flight. The defocusing magnitude was measured experimentally for the ocean swells images, obtained with an airborneS -band radar, and the results are found to be in satisfactory agreement with the model prediction. 相似文献
15.
在近岸河口湍流研究中,实测的湍流资料往往容易受到噪声的影响,导致湍流特征量的估算出现偏差。本征正交分解是一种将流场在能量上进行分解再重构的方法,基于该方法,结合数值实验和野外实测资料,对包含噪声的湍流数据进行了去噪处理。结果表明：（1）本征正交分解能有效去除湍流中的噪声。在进行信号重构时,应将保留能量的百分比与湍流能量占比保持一致。去噪的效果与噪声占比有关,噪声占比越高,去噪效果越明显。（2）在实测资料中,憩流时刻的噪声占比要显著大于非憩流时刻,水平方向的噪声占比要大于垂直方向。经过本征正交分解去噪后,各湍流特征量的估算更加合理。 相似文献
16.
LIU Zhendong LIU Haixing SU Tianyun JIA Zhen LI Xinfang ZHOU Lin SONG Zhuanling 《海洋湖沼学报（英文）》2019,(6):2025-2036
Line integral convolution(LIC)is a useful visualization technique for a vector field.However,the output image produced by LIC has many problems in a marine vector field.We focus on the visual quality improvement when LIC is applied in the ocean steady and unsteady flow field in the following aspects.When a white noise is used as the input in a steady flow field,interpolation is used to turn the discrete white noise into continuous white noise to solve the problem of discontinuity.The"cross"high-pass filtering is used to enhance the textures of streamlines to be more concentrated and continuity strengthened for each streamline.When a sparse noise is used as the input in a steady flow field,we change the directions of background sparse noise according to the directions of vector field to make the streamlines clearer and brighter.In addition,we provide a random initial phase for every streamline to avoid the pulsation effect during animation.The velocities of vector field are encoded in the speed of the same length streamlines so that the running speed of streamlines can express flow rate.Meanwhile,to solve the problem of obvious boundaries when stitching image,we change the streamline tracking constraints.When a white noise is used as an input in an unsteady flow field,double value scattering is used to enhance the contrast of streamlines;moreover,the"cross"high-pass filtering is also adopt instead of two-dimensional high-pass filtering.Finally,we apply the above methods to a case of the surface wave field in typhoon condition.Our experimental results show that applying the methods can generate high-quality wave images and animations.Therefore,it is helpful to understand and study waves in typhoon condition to avoid the potential harm of the waves to people's lives and property. 相似文献
17.
本论文通过对南海北部三次台风过境期间基于浮标观测的海浪谱进行分析,发现虽然大部分成熟的台风海浪谱为单峰结构,但实际上在台风海浪的成长和衰减阶段,双峰谱占据了很大的比例。双峰谱的形成主要是由于风浪和涌浪的叠加以及不同波分量之间的非线性相互作用,我们可以通过能量密度的成长率对谱型变化进行高效的预报。此外,台风海浪的主要波向依赖于台风中心相对观测点的位置,而波向的分散情况在相距台风中心较远的区域无明显规律。本文提出了一个新的六参数波浪谱型拟合双峰谱,其拟合效果相较于前人的谱型更好。通过验证,形状参数和谱宽度之间的理论关系依然适用于单个谱峰。通过分析谱参量的变化特征,证明了谱参量不仅与台风强度和台风路径相关,还存在很强的交互相关。最后通过拟合海浪谱数据,本文得到了台风影响下海浪有效波高和有效周期之间的成长关系,这对海洋工程实际应用具有重要意义。 相似文献
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The method of principal component beamforming described in this paper is an array data reduction method that allows one to observe the statistically uncorrelated components of wave energy arriving at an array of acoustic sensors. The method can be used to process array data so as to observe and identify the sources of noise, both environmental and self noise. After identifying the sources of noise, the method of principal components can be used to discriminate signal from noise. The method can be applied to active systems (subbottom profilers) as well as passive systems. A model of isotropic noise and incident bandlimited plane waves is used to study array resolution and bandwidth effects. Experimental data from a2 times 3 planar acoustic array were used to identify sources of hydro-flow related noise in an underwater vehicle. In all cases studied, the technique provides a maximum spatial information analysis method to the observer. 相似文献
19.
Lao Guosheng Feng Hong Associate Professor Dalian University of Technology Dalian Postgraduate Dalian University of Technology Dalian 《中国海洋工程》1992,(4)
- In this paper, the theoretical calculation of floating breakwater performance in regular waves with arbitrary wave direction is discussed. Under the hypothesis of linearized system and applying the strip theory, we can solve the boundary condition problems of diffraction potential and radiation potential. Introducing the asymptotic expression of the wave velocity potential at infinity and using wave energy conservation, we can separately calculate the transmitted waves generated by the sway, heave and roll motion of the floating breakwater and by the fixed breakwater. Finally, we define the amplitude ratio of the transmitted wave to the incident wave as the transmitted wave coefficient CT which describes the floating breakwater effectiveness. Two examples are given and the theoretical results obtained by the present method agree well with experimental results. 相似文献
20.
经验模态分解(empirical mode decomposition,简称EMD)是反演海洋内波参数的有效方法之一,但由于EMD存在模态混叠等问题,对海洋内波进行参数反演时会产生一定误差。相比较于EMD,变分模态分解(variational mode decomposition,简称VMD)能够有效地抑制模态混叠现象。为了更好地对海洋内波进行参数反演,提出了一种基于VMD对合成孔径雷达(synthetic aperture radar,简称SAR)遥感图像中的内波参数进行自动反演的方法。该方法先对SAR图像进行Canny处理,获取图像中的内波条纹信息,再根据内波传播方向自动选取灰度剖面;然后利用集合经验模态分解(ensemble empirical mode decomposition,简称EEMD)信号特征自适应分解模态函数的特点,再将分解得到的有效模态数作为VMD中参数K的参考值;最后利用VMD分解后的数据进行内波参数反演。试验结果表明:通过对Canny预处理后的条纹信息进行灰度剖面自动选取,解决了人为选取剖面所可能导致的误差;通过对剖面信号进行VMD处理不仅解决了EMD模态混叠的问题,成功地反演出内波的前导波振幅,而且所反演的结果与EEMD反演参数以及实测资料数据吻合得很好。 相似文献