基于BP神经网络的SAR影像水面舰船检测

分析了水面舰船的SAR成像能力和探测优势。在总结已有的舰船检测方法的基础之上,根据舰船目标在SAR图像中的成像特点,提出了利用BP神经网络实现SAR水面舰船目标识别实验。进一步利用形态学方法对检测结果进行修整,结合已知的SAR图像的像元大小,提取舰船的长度和宽度信息,同时利用原始图像的经纬度内插实现舰船目标中心的定位。结果表明,BP神经网络具有很强的自适应性,在低信噪比的情况下,也能够取得良好的效果。     

A new CFAR ship target detection method in SAR imagery

Many ship target detection methods have been developed since it was verified that ship could be imaged with the space-based SAR systems. Most developed detection methods mostly emphasized ship detection rate but not computation time. By making use of the advantages of the K-distribution CFAR method and two-parameter CFAR method, a new CFAR ship target detection algorithm was proposed. In that new method, we use the K-distribution CFAR method to calculate a global threshold with a certain false-alarm rate. Then the threshold is applied to the whole SAR imagery to determine the possible ship target pixels, and a binary image is given as the preliminary result. Mathematical morphological filter are used to filter the binary image. After that step, we use the two-parameter CFAR method to detect the ship targets. In the step, the local sliding window only works in the possible ship target pixels of the SAR imagery. That step avoids the statistical calculation of the background pixels, so the method proposed can much improve the processing speed. In order to test the new method, two SAR imagery with different background were used, and the detection result shows that that method can work well in different background circumstances with high detection rate. Moreover, a synchronous ship detection experiment was carried out in Qingdao port in October 28, 2005 to verify the new method and one ENVISAT ASAR imagery was acquired to detect ship targets. It can be concluded from the experiment that the new method not only has high detection rate, but also is time-consuming, and is suitable for the operational ship detection system.     

航行船舶真风误差源分析

真风对海上航行的船舶有重要的气象导航意义,若真风测算不准确,会给导航员造成误判,影响船舶安全航行,但在船舶等运动平台上真风无法直接测量,只能依靠矢量模型计算间接获取。根据真风解算模型和误差传播规律,推导了船舶真风误差模型。在矢量模型中,航行船舶真风误差主要来自于船风和相对风的计量误差,船风的计量误差主要是由于航速航向的选取问题导致的误差,相对风的测量误差主要包括传感器自身精度、安装误差、平台姿态影响和系统性干扰误差等几个方面。以船舶转向过程为例,分析了航行风与相对风的变化规律,结合船体运动姿态,加入运动补偿修正量,建立了船舶转向式真风补偿模型。     

西沙群岛附近海域船舶尾迹水体遥感反射率特性的实验测量与分析

利用海上实验现场测量船舶的尾迹气泡群对西沙群岛附近海域一类水体海水光学特征(例如归一化离水辐亮度、遥感反射率)的影响,为通过星载光学传感器遥感获取船舶尾迹信息提供理论依据。实验证明,在可见光和近红外波段,船舶含气泡尾迹不仅在幅度上、也在谱形上改变海水遥感反射率,作为结果,尾迹气泡使得海水变得更绿;同时,随着观测点在尾迹中的位置距目标船的接近,气泡密度不断增大,反射率也随之增强。     

Experimental Investigation of the Decay from A Ship’s Propeller

In the present study,an experimental investigation of the decay of the maximum velocity and its turbulent characteristics behind a ship propeller,in "bollard pull" condition(zero speed of advance),is reported.Velocity measurements were performed in laboratory by use of a Laser Doppler Anemometry(LDA) measurement system.Earlier researchers described that the maximum axial velocity is constant at the initial stage of a ship’s propeller jet(Fuehrer and Rmisch,1977;Blaauw and van de Kaa,1978;Berger et al.,1981;Verhey,1983) as reported in a pure water jet(Albertson et al.,1950;Lee et al.,2002;Dai,2005),but a number of researchers disagreed with the constant velocity assumption.The present study found that the maximum axial velocity decays in the zone of flow establishment and the zone of established flow with different rates.The investigation provides an insight into the decays of both the maximum velocity and the maximum turbulent fluctuation in axial,tangential and radial components and the decay of the maximum turbulent kinetic energy.Empirical equations are proposed to allow coastal engineers to estimate the jet characteristics from a ship’s propeller.     

船舶海洋气象导航的业务概况与发展现状

通过对多家船舶海洋气象导航公司和机构的介绍,概括了国内外气象导航的业务和发展。文章分析结果表明,国外气象导航业务发展历史悠久,技术储备雄厚,业务体系完善,占据了全球气象导航业务的大部分市场份额。国内气象导航的发展历程较短,技术力量薄弱,业务量相对较少。当前国内的气象导航服务正在努力开拓创新,在信息化背景下逐步开展多样化的平台建设和产品研发,并取得了良好的进展。     

海上主航迹带边界统计推断与海西航路警戒区布局优化分析

台湾海峡是东北亚各国与东南亚、印度洋沿岸各国间的海上捷径,其交通主流是通行海峡的南北向航次,然而海峡两岸启动大三通后,穿越海峡的客货运船舶日益增多,导致闽台直航航次与台湾海峡南北干线主交通流交叉现象凸显,台湾海峡西侧水域冲突日益加剧。本文根据船舶轨迹观测数据,抽样出通行海峡南北及横穿海峡的航次样本,应用轨迹栅格化方法建立统计推断模型,以概率形式表达南北干线、两岸直航的海运利用分布,推断出2种交通流的主航迹带,识别南北向交通主流与两岸直航交通支流的显著冲突区,以此调整现有警戒区设置方案。研究结果表明：轨迹统计推断法能定量化分析海西现有交通流模式,易于辨识横越海峡的船舶与通行海峡在航船舶的冲突区中心,为优化警戒区布局提供有效的方法支撑;调整后的海西警戒区中心可与台湾本岛西岸港口外侧的直航船舶通过点对接,形成海峡两岸直航的固定航线,可降低台湾海峡船舶冲突隐患,规范台湾海峡的船舶交通秩序。     

汛期江上工程钻探施工实践

通过工程实例,着重介绍了汛期在江上进行桥基勘察施工时,钻船及设备的选择,钻船拼装和抛锚定位方法,钻进工艺以及机上余尺、回次进尺的计算方法等,重点强调了江上钻探施工的相关注意事项。     

基于OpenLayers和MongoDB的船舶信息管理系统开发

船舶数据的管理和可视化对航道、船舶管理具有重要意义。大量快速更新的船舶位置信息和影像数据,对数据存储、检索以及可视化提出了较高的要求。本文结合实际应用需求,基于非关系型数据库MongoDB和开源地图API设计并开发船舶信息管理系统。该系统将船舶和热点区域数据存储在MongoDB中,可在浏览器中高效同步显示大量空间数据,提供属性查询、空间检索和统计制图等功能,并且可在线编辑数据库中的热点区域数据。本系统主要解决了MongoDB数据库中空间数据高效检索,BSON文档格式和Geo JSON地理要素格式的转换,数据库中空间数据在线编辑等问题,为船舶信息化管理提供了支持。     

Ship Hull Slamming Analysis with Nonlinear Boundary Element Method

A boundary element method is developed for calculating the flare ship hull slammingproblem.The nonlinear free surface elevation and the linear element assumption are employed.The meth-od has been verified by comparisons with results for the water entry of wedges with various deadriseangles.Numerical results show that the pressure distribution varies greatly with the ship hull with differentcurvilinear equations,and the slamming features are also different.From the numerical simulation,the au-thors found that the structural damage of the flare hull might be caused by the increasing hydrodynamicpressure over an extensive area on the flare when the upper part of the flare comes into contact with water.