Estimation of sea clutter inherent Doppler spectrum from shipborne S-band radar sea echo

Measurement of shipborne radar sea echo is instrumental in collecting the sea clutter data in open sea areas.However,the ship movement would introduce an extra Doppler component into the spectrum of the sea clutter,so the sea clutter inherent spectrum must be estimated prior to investigating the sea clutter Doppler characteristics from the shipborne radar sea echo.In this paper we show some results about a shipborne sea clutter measurement experiment that was conducted in the South China Sea in a period between 2017 and 2018;abundant clutter data have been collected by using a shipborne S-band clutter measurement radar.To obtain the sea clutter inherent Doppler spectrum from these data,an estimation method,based on the mapping relationship between the shipborne clutter spectrum and the inherent clutter spectrum,is proposed.This method is validated by shipborne clutter data sets under the same measuring conditions except for the ship speed.Using this method,the characteristics of the Doppler spectrum lineshapes in the South China Sea are calculated and analyzed according to different sea states,wave directions,and radar resolutions,which can be instrumental in designing the radar target detection algorithms.

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.

CHARACTERISTICS OF FREQUENCY SPECTRUM VARIATION OF INTRASEASONAL OSCILLATION OF CONVECTION DURING SOUTH CHINA SEA SUMMER MONSOON

Datasets of equivalent temperature of black body (TBB) and sea surface temperature (SST)ranging from 1980 to 1997 are used to diagnose and analyze the characteristics of frequency spectrum andstrength of intraseasonal variation of convection. The relationship between the strength of intraseasonaloscillation of convection, strength of convection itself and SST in the South China Sea (SCS) is studied. It isshown that, there are distinguishable annual, interannual and interdecadal variations in both strength andfrequency spectrum of intraseasonal variation of convection in SCS. There are connections between strength ofconvection, strength of ISO1 in the summer half (s.h.) year and SST in ensuing winter half (w.h.) year in SCS.The strong (weak) convection and strong (weak) ISO1 are associated with negative (positive) bias of SST inensuing w.h. year in SCS.

Doppler Spectrum Analysis of Time-Evolving Sea Surface Covered by Oil Spills

Based on the model of a contaminated sea surface that was proposed by Lombardini et al., the influence of the damping effect of oil films on the sea surface roughness spectrum and the geometrical structure of the sea surface is examined in detail by comparing with a clean sea surface. Fhrthermore, based on a quasi-stationary algorithm, a time series of backscattered echoes from a time-evolving sea surface covered by oil slicks is obtained by utilizing the frequency-domain numerical method of the parallel fast multiple method. Then, the Doppler spectrum is evaluated by performing a standard spectral estimation technique. Finally, the influence of the oil film damping effect on the Doppler spectrum of the backscattered echoes from time-evolving sea surface is investigated in detail by making a comparison of the Doppler spectrum of an oil-covered sea surface with the Doppler spectrum of a dean sea surface. The numerical simulations show that the damping effect of oil films has an influence on the Doppler spectrum signature for both horizontal-to-horizontal and vertical-to-vertical polarizations.

Observed typhoon wave spectrum in northern South China Sea

To describe both the way in which a wave spectrum grows and the growth processes of realistic wave conditions,the dependence relationship between the spectrum parameters and wind parameters must be obtained. Based on data measured in 2010 by a Wave Rider buoy,which was deployed in the South China Sea at coordinates 21.89°N,115.13°E,we evaluated the wave spectrum in the sea area when affected by three typhoons:Conson,Chanthu,and Megi. The Joint North Sea Wave Project spectrum was parameterized based on the observed wave spectrum. We proposed a spectrum with three parameters:the dimensionless lowest moment of the spectrum,dimensionless peak frequency,and spectrum width. The relationships between these spectral parameters and the dimensionless fetch were also discussed.

Bandwidth Scale for Frequency Spectrum of Sea Waves

It is well known that energy spectrum bandwidth should be able to reflect the degree of energy concentration. However, the commonly used bandwidth factors defined by Longuet-Higgins could not fit the concept satisfactorily. A new kind of spectrum bandwidth scale factor with a clear physical meaning is given in the present paper and a constant is obtained which reveals the intrinsic characteristics of sea waves. Thereby a universal relationship between significant wave height of sea waves and spectrum bandwidth is established.

A Proposed Frequency Spectrum for Fully Developed Wind Waves by Revisiting P-M Spectrum

It is generally believed that the equilibrium range of wind wave spectrum is in the form of the-4 rather than-5 power law.However,in the widely applied P-M spectrum the equilibrium range is given in the form of-5 power law.In the present paper,a spectrum for full development of wind waves is proposed using the form of the Neumann spectrum,but adopting the-4 power law for the equilibrium range.The proposed spectrum has been verified with NDBC buoy data and could be a substitute for the P-M spectrum.

Outer frequency spectrum of sea waves and its equilibrium range

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Improved significance testing of wavelet power spectrum near data boundaries as applied to polar research

When one applies the wavelet transform to analyze finite-length time series, discontinuities at the data boundaries will distort its wavelet power spectrum in some regions which are defined as a wavelength-dependent cone of influence （COI）. In the COI, significance tests are unreliable. At the same time, as many time series are short and noisy, the COI is a serious limitation in wavelet analysis of time series. In this paper, we will give a method to reduce boundary effects and discover significant frequencies in the COI. After that, we will apply our method to analyze Greenland winter temperature and Baltic sea ice. The new method makes use of line removal and odd extension of the time series. This causes the derivative of the series to be continuous （unlike the case for other padding methods）. This will give the most reasonable padding methodology if the time series being analyzed has red noise characteristics.

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.

Rotary spectrum analysis of tidal current in the southern Yellow Sea

A complete set of one-month Acoustic Doppler Profiler (ADP) current data at a station in the southern Yellow Sea (SYS) is analyzed using the rotary spectrum method. The results revealed different rotary properties between barotropic and baroclinic tidal currents. The barotropic and baroclinic tidal currents rotate elliptically counter-clockwise and clockwise, respectively. Meanwhile, baroclinic bottom tidal currents are almost along-isobath. The baroclinic cross-isobath velocities attenuate quickly at the bottom, implying important effects of bottom topography on the cross-isobath motions.

SINGULAR CROSS SPECTRUM APPLIED ON DIAGNOSTIC ANALYSIS OF AIR-SEA INTERACTION

The Singular Cross Spectrum Analysis (SCSA) method was employed to investigate the coupledperiods of air-sea/mid-low circulation interaction using 1951-1993 500-hpa geopotential heights and the seasurface temperature (SST) in the Northern Hemisphere. Results show that air-sea correlation is noticeable on the3-7 year scale which is similar to ENSO circle. In this sense, ENSO is a Strong signal. Quasi-ten/quasi-four yearperiods are prominent in the mid-low interaction, and quasi-if our year oscillation is uniform with the ENSO circle.Studies indicate that the mid-low interaction possess quasi-ten year oscillation beside being affected by ENSO.

基于江苏海域定点观测资料的双峰谱谱型研究

江苏海域作为全国海上风电重点建设海域,走向远海是未来发展的主趋势,外海开敞海域涌浪成分较多,海浪谱往往以双峰谱的形式出现,因此双峰谱海浪的谱型特征需要进一步深入研究,为海上施工提供参考依据。基于浮标测站2018年全年观测数据,经过异常值检验、双峰谱识别后得到1 223笔双峰谱数据,进而研究江苏海域波浪双峰谱谱型特征,对比不同典型双峰谱谱型并展开实测双峰谱的拟合,提出了修正谱宽参量,探究了修正系数、峰升高因子、谱宽参量间的依赖关系,得到了双峰谱拟合谱型表达式。结果表明:基于北大西洋海域提出Ochi-Hubble谱系及基于挪威海域提出的Torsethaugen谱并不适用于江苏海域双峰谱谱型,本文提出的双峰JONSWAP拟合谱具有自适应性,可以科学合理地描述江苏海域双峰谱谱型,并推广应用于不同风场、地形条件的海域中。

基于P-M谱的二维各向异性分层海面电磁散射研究

为了得到基于P-M谱的二维各向异性分层海面电磁散射特性,以便为海洋遥感、海上目标检测与识别等领域的应用提供理论依据,采用微扰法研究了平面波入射分层介质粗糙面的电磁散射特性,结合海面P-M谱推导出了平面波入射时的散射系数计算公式,通过数值计算获得了HH极化下中间介质的介电常数和厚度、摩擦风速、风区范围、观察方向与逆风方向之间夹角和入射波频率对双站散射系数的影响,得到了分层海面电磁散射系数的基本特征、分区特征和随频率变化的特征。

基于Davenport风速谱的适配器海上动平台分离动力学研究

海上发射作为一种新兴的发射方式,与传统发射方式相比运载能力更强,在发射地点的灵活性和适配器落点的安全性方面有巨大的优势。为研究海上动平台发射过程的安全性问题,建立了海上垂直发射系统多体动力学模型。基于六自由度海浪摇荡激励和随机风载荷作用,通过实时更新适配器姿态和气动载荷,得到了适配器气动载荷变化过程和洒落轨迹。结果表明,由于存在初始分离速度,适配器在气动载荷作用下发生翻转,风载荷的存在使得适配器在初始分离阶段与火箭发生碰撞,适配器最大洒落距离为26.645 m,落点分布远离发射装置,但有落至动平台平面的风险。

基于卫星海面高度资料的太平洋海区涡旋能谱分析

在空间均匀和各向同性的假定下,地转湍流理论认为涡旋动能随尺度分布遵循k–n定律(k为波数)。但实际海洋受边界、地形、层结等,具有明显的非均匀、各向异性特征。鉴于此,我们基于近30a卫星高度计资料,分别计算了热带、副热带、中高纬度等海洋涡旋强度不同区域的海面高度异常(SSHA)波数谱,进而利用线性回归拟合方法估算出中尺度波段上SSHA波数谱的斜率,并与地转湍流理论预测进行了对比。研究结果显示:SSHA波数谱从赤道到中高纬度逐渐变陡,其斜率由–4减到–5,基本符合赤道线性波动理论和准地转湍流理论的预测。SSHA波数谱斜率存在纬向与经向差异,例如在赤道地区,纬向谱比相应的经向谱陡;而在南极绕极流区域,经向谱斜率大于纬向谱斜率。SSHA波数谱斜率的各向异性表明海洋中尺度运动受β效应影响,具有明显的经向和纬向差异。以上结果表明,海洋中尺度运动介于准二维和三维之间,不能用一个全球普适的湍流理论模型来描述。

BI@ZIF-8/EP涂层的制备及在深海压力下的防护性能研究

目的制备负载苯并咪唑(BI)的BI@ZIF-8粒子,研究BI@ZIF-8/EP涂层在2种静水压力下的失效行为。方法制备并表征BI@ZIF-8粒子。制备BI@ZIF-8/EP涂层,在常压(0.1 MPa)和模拟深海压力(6 MPa)开展浸泡实验。通过微观形貌、失光率、色差、附着力、红外光谱、电化学阻抗谱等手段进行涂层失效行为对比分析。结果成功制备了BI@ZIF-8粒子;在相同压力条件下,BI@ZIF-8/EP涂层具有更高的附着力和阻抗值;同种涂层在6 MPa下退化更加严重,附着力和阻抗值下降速率增大;随着浸泡时间的延长,6 MPa下BI@ZIF-8/EP涂层中的BI特征峰强度明显减弱,2种涂层的主要特征峰强度均有下降。结论ZIF-8粒子中的咪唑基,能增加环氧涂层交联密度,降低侵蚀性粒子渗透速率;高静水压能显著加速侵蚀性粒子向涂层内部的扩散,并加速有机涂层失效进程;BI分子和2-Melm分子中N原子的孤电子对与Fe原子的空轨道能在金属基体表面形成吸附膜,并且Zn^(2+)和OH^(−)能在金属基体表面形成沉积膜,有效减缓了金属腐蚀。此外,2种涂层的退化机制不受静水压力升高的影响。

基于改进波形聚类方法的复合河道砂体沉积微相预测--以渤海A油田为例

渤海新近系河湖过渡带复合河道砂体叠置关系复杂、相带变化剧烈,利用传统地震属性划分沉积微相多解性较强。提出了改进振幅谱距离-K中心聚类方法并将其应用于复合河道砂体沉积微相预测。方法包括两个方面:①以测井标定沉积微相对应的典型波形作为初始聚类中心以及聚类中心更新过程中的约束条件;②利用振幅谱距离评价波形之间的差异,进一步提升波形聚类精度。根据渤海新近系A油田地质条件设计复合河道砂体三维模型,模型试验结果证实改进后的方法微相预测准确率达95%,相比传统K均值聚类算法精度提升15%,较好地区分了泥岩、单期河道边部、单期河道主体、河道边部叠置、河道边部与主体叠置、河道主体叠置(或多期叠置)共6种河道不同部位或叠置样式。利用改进后的方法指导A油田10个砂体沉积微相划分,将大型砂体S沉积微相划分为分流河道、河口坝、席状砂、决口河道、分流间湾、天然堤6类,指导开发方案中优先动用分流河道、河口坝等优势微相的地质储量,证明了方法的实用价值。

烃相态分析录井技术在东海新探区油气识别中的应用

随着东海海域油气勘探的不断深入,勘探难度增大,部分探区油气成藏条件复杂。受限于储层岩性复杂、非均质性强及流体性质多变的影响,储层流体准确识别难度较大,而传统的录井、测井技术在识别中深层复杂流体的性质仍存在不足。为了解决东海探区流体评价难题,引入烃相态分析录井技术。该技术利用检测到的烃类物质组成以及含量的变化规律来定性、定量地快速评价储层的流体,通过在东海某新区块勘探作业中的实际应用,证实该技术具有参数丰富、分析速度快、仪器稳定性好等特点,有利于储层流体性质的快速识别,助力解决东海新探区的油气解释评价难题。

Research on Motion Performance of the Mobile Double-Causeway Pier System

Mobile offshore double-causeway pier system, a type of seashore unloading equipment, consists of two groups of multiple connected semi-submersible modules. This structure has wide application because most of the middle or mini type of vessels and ships can be moored to it. Based on the analysis of computational methods of multi-body motion response, a hydrodynamic model is set up and the three-dimensional potential theory in finite depth is adopted to calculate the three-dimensional motion response of this system. The double P-M spectrum is used to analyze the motion response in irregular waves. Different wave directions are specially taken into consideration, due to their various effects to the motion response. Furthermore, the calculated result is compared with that of the experiment, and it is proved that sway, heave, pitch and yaw motion are greatly constrained by mooring system. The comparison also indicates that the model can forecast the motion performance of the target, and that the calculated result can also be used as reference in connector and mooring system design.