An ocean current inversion accuracy analysis based on a Doppler spectrum model

Microwave remote sensing is one of the most useful methods for observing the ocean parameters. The Doppler frequency or interferometric phase of the radar echoes can be used for an ocean surface current speed retrieval,which is widely used in spaceborne and airborne radars. While the effect of the ocean currents and waves is interactional. It is impossible to retrieve the ocean surface current speed from Doppler frequency shift directly. In order to study the relationship between the ocean surface current speed and the Doppler frequency shift, a numerical ocean surface Doppler spectrum model is established and validated with a reference. The input parameters of ocean Doppler spectrum include an ocean wave elevation model, a directional distribution function, and wind speed and direction. The suitable ocean wave elevation spectrum and the directional distribution function are selected by comparing the ocean Doppler spectrum in C band with an empirical geophysical model function（CDOP）. What is more, the error sensitivities of ocean surface current speed to the wind speed and direction are analyzed. All these simulations are in Ku band. The simulation results show that the ocean surface current speed error is sensitive to the wind speed and direction errors. With VV polarization, the ocean surface current speed error is about 0.15 m/s when the wind speed error is 2 m/s, and the ocean surface current speed error is smaller than 0.3 m/s when the wind direction error is within 20° in the cross wind direction.

Three-dimensional dynamic sea surface modeling based on ocean wave spectrum

In conventional marine seismic exploration data processing,the sea surface is usually treated as a horizontal free boundary.However,the sea surface is affected by wind and waves and there often exists dynamic small-range fluctuations.These dynamic fluctuations will change the energy propagation path and affect the final imaging results.In theoretical research,different sea surface conditions need to be described,so it is necessary to study the modeling method of dynamic undulating sea surface.Starting from the commonly used sea surface mathematical simulation methods,this paper mainly studies the realization process of simple harmonic wave and Gerstner wave sea surface simulation methods based on ocean wave spectrum,and compares their advantages and disadvantages.Aiming at the shortcomings of the simple harmonic method and Gerstner method in calculational speed and sea surface simulation effect,a method based on wave equation and using dynamic boundary conditions for sea surface simulation is proposed.The calculational speed of this method is much faster than the commonly used simple harmonic method and Gerstner wave method.In addition,this paper also compares the new method with the more commonly used higher-order spectral methods to show the characteristics of the improved wave equation method.

非合作水声通信辐射源个体识别初探

辐射源个体识别是非合作水声通信信号调制样式识别之后进一步获取对方通信设备固有信息的重要途径。为解决海洋信道中非合作水声通信辐射源个体识别的难题,文章对水声通信发射机性能差异进行分析,重点对水声发射机根升余弦滚降滤波器的非线性进行描述,并针对非合作水声通信信号先验信息缺失且信号具有循环平稳性的特点,提出了一种利用循环谱等值线图区分不同辐射源的个体识别方法。以二进制相移键控信号为例,进行不同滚降因子条件下循环谱特征的仿真分析。研究结果验证了当信噪比不小于3 dB时文中所提辐射源个体识别方法的可行性。

面向海浪遥感卫星标定的漂流波浪浮标关键技术研究

在精细化海洋观测领域,遥感卫星海浪方向谱的获取存在精度低、累积误差大等问题,设计了一种基于Transformer神经网络的海浪方向谱估计方法,通过引入稀疏自注意力机制以及物理引导模块等,实现海浪方向谱的高精度表达;海上试验测试结果表明,新提出的海浪方向谱估计方法与传统海浪方向谱估计方法相比,文章提出的模型估计方向谱更符合理论谱形,伪峰较少,平滑性和一致性方面表现较好,并且对数据噪声的容忍度更高。同时,设计了一种基于人工智能芯片的漂流波浪浮标系统,通过AI软硬件系统对不同任务进行动态调度分配,实现浮标低功耗运行,有效提升了波浪测量性能及海上工作时间,是遥感卫星高精度获取大范围、长时序全球性海洋观测数据的一种有效补充。

Parameterized first-guess spectrum method for retrieving directional spectrum of swell-dominated waves and huge waves from SAR images

A method to retrieve ocean wave spectra from SAR images, named Parameterized First-guess Spectrum Method （PFSM）, was proposed after interpretation of the theory to ocean wave imaging and analysis of the drawbacks of the retrieving model generally used. In this method, with additional information and satellite parameters, the separating wave-number is first calculated to determine the maximum wave-number beyond which the linear relation can be used. The separating wave-number can be calculated using the additional information on wind velocity and parameters of SAR satellite. And then the SAR spectrum can be divided into SAR spectrum of wind wave and of swell according to the result of separating wave-number. The portion of SAR spectrum generated by wind wave, is used to search for the most suitable parameters of ocean wind wave spectrum, including propagation direction of ocean wave, phase speed of dominating wave and the angle spreading coefficient. The swell spectrum is acquired by directly inversing the linear relation of ocean wave spectrum to SAR spectrum given the portion of SAR spectrum generated by swell. We used the proposed method to retrieve the ocean wave spectrum from ERS-SAR data from the South China Sea and compared the result with altimeter data. The agreement indicates that the PFSM is reliable.

A joint method to retrieve directional ocean wave spectra from SAR and wave spectrometer data

This paper proposes a joint method to simultaneously retrieve wave spectra at dif ferent scales from spaceborne Synthetic Aperture Radar(SAR) and wave spectrometer data. The method combines the output from the two dif ferent sensors to overcome retrieval limitations that occur in some sea states. The wave spectrometer sensitivity coeffi cient is estimated using an ef fective signifi cant wave height(SWH), which is an average of SAR-derived and wave spectrometer-derived SWH. This averaging extends the area of the sea surface sampled by the nadir beam of the wave spectrometer to improve the accuracy of the estimated sensitivity coeffi cient in inhomogeneous sea states. Wave spectra are then retrieved from SAR data using wave spectrometer-derived spectra as fi rst guess spectra to complement the short waves lost in SAR data retrieval. In addition, the problem of 180° ambiguity in retrieved spectra is overcome using SAR imaginary cross spectra. Simulated data were used to validate the joint method. The simulations demonstrated that retrieved wave parameters, including SWH, peak wave length(PWL), and peak wave direction(PWD), agree well with reference parameters. Collocated data from ENVISAT advanced SAR(ASAR), the airborne wave spectrometer STORM, the PHAROS buoy, and the European Centre for Medium-Range Weather Forecasting(ECMWF) were then used to verify the proposed method. Wave parameters retrieved from STORM and two ASAR images were compared to buoy and ECMWF wave data. Most of the retrieved parameters were comparable to reference parameters. The results of this study show that the proposed joint retrieval method could be a valuable complement to traditional methods used to retrieve directional ocean wave spectra, particularly in inhomogeneous sea states.

海洋环境对海洋低频水声扩频通信的影响分析

水声通信是水下舰艇通信的主要手段,从基本物理原理的角度仿真分析海洋环境对水声扩频信号的可能影响,相较于实际海试实验降低了实验难度。选取等熵性质的非均匀介质中的声传播波动方程推导,建立水声信道动力学模型,分析了不同幅度海洋背景噪声下和不同海水密度区间中水声扩频信号传播后的幅频特性和通信误码率的变化。文中,利用Matlab进行微分方程数值解求解和水声传播信号的幅频特性分析。结果表明:1)海洋背景噪声在信噪比高于-20 dB时满足通信准确度要求;2)海水密度的变化对水声扩频通信准确度没有显著影响。

Polarimetric entropy of the ocean surface with a two-scale scattering model

The relationships among an ocean wave spectrum,a fully polarimetric coherence matrix,and radar parameters are deduced with an electromagnetic wave theory.Furthermore,the relationship between the polarimetric entropy and ocean wave spectrum is established based on the definition of entropy and a twoscale scattering model of the ocean surface.It is the first time that the polarimetric entropy of the ocean surface is presented in theory.Meanwhile,the relationships among the fully polarimetric entropy and the parameters related to radar and ocean are discussed.The study is the basis of further monitoring targets on the ocean surface and deriving oceanic information with the entropy from the ocean surface.The contrast enhancement between human-made targets and the ocean surface with the entropy is presented with quad-pol airborne synthetic aperture radar（AIRSAR） data.

Ocean wave diffraction in near-shore regions observed by Synthetic Aperture Radar

Observation and analysis of ocean wave diffraction in near-shore and near-island region was performed with Synthetic Aperture Radar （SAR） data, using an optimized retrieval method named parameterized first-guess spectrum retrieval method. The results retrieved from ERS-SAR and ENVISAT-ASAR images showed that, in the region sheltered by land jut, the energy of long waves is reduced by 10%-20% and that the propagation direction of long waves is changed due to the effect of topography. In the shadow zone behind the island, ocean wave can propagate along the seashore instead of perpendicular to the coastline, as shown by SAR images.

Application of sequency spectral method toocean and atmosphere data analysis

The chaotic systems of average monthly air temperature of Qingdao (SATQ) and the day SST of equatorial local area (DSSELA) are firstly studied by means of the sequency spectral method. It is shown that SATQ contains one-a period of predominant oscillation, two-a periods lower frepqency oscillation and 90-d, 63-d, 50-d, 40-d and 29-d lower frequency periods oscillation in DSSELA. Further more, the discrepancies between sequency spectrum and frequency spectrum are compared in this paper.

A Processing Workflow for Ocean Bottom Cable Dual-Sensor Acquisition Data: A Case of 3D Seismic Data in Bohai Bay

The technique of ocean bottom cable (OBC) dual-sensor acquisition is an effective method to suppress the ghost wave and the reverberation at the receiver. With the advent of this technique, the processing method has become the key to the effective use of the OBC dual-sensor data. This paper has developed a new set of processing workflow based on the principle of combining the hydrophone and geophone data. This new process was applied to the OBC data acquired in Bohai area. The actual processing results show that the ghost and the reverberation are attenuated effectively. The frequency energy of the first notch point of the hydrophone data increased from −22 dB to −13 dB, and the frequency energy of the first notch point of the geophone data increased from −18 dB to −10 dB. The spectral characteristics of the dual-sensor data are more reasonable. The frequency spectrum is broadened and richer, and the resolution of the stack profile is improved greatly.

Theory and Analysis for First-Order Interaction Between HF Radio Waves and Ocean Waves

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目标海域中航行船舶横摇谱密度值的预报策略

横摇功率谱密度的预报是船舶耐波性分析的重要环节。本文以带有舭龙骨的船舶模型DTMB 5512为研究对象,采用CFD方法对船舶横摇频率响应进行计算。首先利用重叠网格法建立船舶在自由液面中横摇运动的数值模型,进而在可靠验证的基础上,数值研究航速、遭遇频率和波浪方向对船舶横摇响应的影响;接着,基于P-M波谱公式推导出海浪自相关函数表达式,结合目标海域的海浪数据对其进行参数修正,获取该目标海域的自相关函数,从而得到目标海域海浪谱;最后,将频率响应谱与该目标海浪谱相结合,得到横摇谱密度。

基于中法海洋卫星波谱仪观测的一维海浪谱模型对比

海浪谱模型不仅能表征粗糙海表面,还能揭示海浪能量随波数和方向的分布,为海洋探测等研究和应用提供必要信息。中法海洋卫星搭载的波谱仪可实现全球海浪方向谱的空间观测。根据现有海浪谱模型和海浪谱观测的发展现状,对波谱仪观测的海浪参数进行统计特征分析,在波谱仪观测的波数范围内(0.01~0.25rad·m^(–1)),进行不同海态下实测海浪谱与以Apel谱、Elfouhaily谱和Goda谱为代表的波高谱和曲率谱模型的比较,得到现有海浪谱观测与上述三种谱模型的差异,并结合海浪参数统计特征,对产生差异的原因进行讨论分析。结果表明,现有谱与波谱仪观测的差异来自于其对海态的不完全表达,且所表示的海态在自然状态中仅占有限比例。研究结论可以为海浪谱模型和观测的后续研究提供支持。

基于二维海浪谱的风涌浪分离方法研究

海浪通常以风浪和涌浪混合的形式存在。二者的成长、消衰、传播和破坏机制各不相同,实现风涌浪分离对海洋研究和工程应用具有重要意义。基于斯里兰卡汉班托塔海域的实测数据,讨论了传统波龄法中波龄阈值的选取问题,并对汉班托塔海域的海浪特征进行分析,最后利用波龄法对新提出的不依赖风速风向信息的超射法进行了研究。结果表明,波龄阈值取1.7时最为合理。汉班托塔海域为外海涌浪主导。超射法对外海涌浪的识别结果与波龄法一致,而对高频位置的风浪和局地涌浪给出了不同的结果,这主要是由海浪物理特性的改变慢于风速风向的变化引起。

南海OBC水听器分量随机噪声性质分析

针对海洋资源勘探受限于采集技术和环境的限制,以及OBC(Ocean Bottom Cable)记录通常含有大量随机噪声,对有效反射信息的辨识带来不利影响,提出了基于序列能量分布的平稳性检验方法,并利用多椎体法对OBC随机噪声的功率谱特性和平稳性进行了分析研究。使用南海某地采集的OBC实际噪声资料作为分析数据集。研究结果表明OBC随机噪声是一种色噪声序列和弱非平稳时间序列,噪声能量主要集中于低频部分。同时结合海洋勘探环境特点,论证了结论合理性,这对OBC随机噪声特性的基础研究具有一定的实际意义和应用前景。

大跨度铁路桥梁海、陆风场差异性研究

为研究桥址区海、陆风场的差异及其对铁路桥梁的影响,开展桥址区海、陆风场数值模拟和桥梁风荷载数值计算研究。考虑海面粗糙度、海气交换等因素影响,从风剖面、风谱、相干函数3个角度进行海洋风场与陆地风场的对比,进而实现海、陆风场的数值模拟和风荷载计算。结果表明:海、陆风场紊流特性和空间相干性差异显著,内陆铁路桥梁较海洋铁路桥梁风荷载的阻力、升力和力矩分别增加6.1%、5.5%和5.9%,但由于海洋风谱的能量高于陆地风谱,海洋铁路桥梁所受的抖振力高于内陆铁路桥梁。

海洋表面流的高频雷达遥感

解释了利用高频雷达探测海洋表面流的基本原理，简要介绍了新研制的海态监测分析雷达OSMAR的组成及其工作流程，着重分析了利用OSMAR探测北部湾海流的实验结果．

高频天波返回散射回波谱实验研究

用中国电波传播研究所高频天波返回散射探测站进行的我国首次陆地 /海洋回波谱的实验研究 ,其中包括自行研制的实验设备 ,实验结果。介绍了获得海洋回波谱的信号处理方法 ,并由海洋回波Doppler谱计算了电离层状参数和风向、海流等海洋状态参数。

基于线性海浪理论的海浪数值模拟

概述了海浪理论发展的历史和现状,对几种海浪研究方法进行了简要说明。详细论述了基于线性海浪理论进行海浪数值模拟的线性叠加法和线性过滤法,给出了具体的数值算法,讨论了工程应用数值模拟与视觉效果模拟之间的区别及各自的处理方法。并分析了工程应用领域内进行海浪数值模拟所采用的其他一些理论和方法,指出了现有海浪数值模拟方法存在的局限性。最后,对海浪数值模拟研究的发展趋势进行了展望。