Accuracy of the spatial representation of the seafloor with bathymetric sidescan sonars

When isobath maps of the seafloor are constructed with a bathymetric sidescan sonar system the position of each sounding is derived from estimates of range and elevation. The location of each pixel forming the acoustic backscatter image is calculated from the same estimates. The accuracy of the resulting maps depends on the acoustic array geometry, on the performances of the acoustic signal processing, and on knowledge of other parameters including: the platform's navigation, the sonar transducer's attitude, and the sound rays' trajectory between the sonar and the seafloor. The relative importance of these factors in the estimation of target location is assesed. The effects of the platform motions (e.g. roll, pitch, yaw, sway, surge and heave) and of the uncertainties in the elevation angle measurements are analyzed in detail. The variances associated with the representation (orientation and depth) of a plane, rectangular patch of the seafloor are evaluated, depending on the geometry of the patch. The inverse problem is addressed. Its solution gives the lateral dimensions of the spatial filter that must be applied to the bathymetric data to obtain specified accuracies of the slopes and depths. The uncertainty in the estimate of elevation angle, mostly due to the acoustic noise, is found to bring the main error contribution in across-track slope estimates. It can also be critical for along-track slope estimates, overshadowing error contributions due to the platform's attitude. Numerical examples are presented.On leave at the Naval Research Laboratory, Code 7420, Washington D.C. 20375-5350, U.S.A.     

勘探目标优选思路及方法探讨

勘探目标优选是勘探决策的重要依据,从目前常用评价方法入手,梳理地质认识与评价方法之间的辨证关系,对方法中的存在问题提出解决思路和调整方案,并举例检验。     

冰区海洋平台LRFD方法的系数标定及优化设计

对渤海北部结冰海域海洋平台的ＬＲＦＤ设计表达式的系数进行了标定,并在此基础上以实际平台为例,进行了优化计算。     

海底沉放结构物的位移监测

船坞内制作的大型结构物浮运沉放到海底的支撑基础上之后,受其自重及基础强度等因素的影响,在其初期会有一个明显沉降过程;为研究其沉降规律性,须对其进行监测.由于结构物在海水面以下,其底部位置靠测量设置的塔目标位置反求.通过对某电厂取水工程的海底取水头监测,介绍了监测方法及其沉降数据规律.     

捕食者不同目标策略下的鱼群结构变化仿真与研究

在海洋生态环境中,食物链上层捕食者对下层鱼群的捕猎行为可以被普遍地观察到,捕食者攻击的策略以及鱼群的防御机制是海洋捕猎行为的关键。本文构建了鱼群行为模型并对捕食者目标选择策略进行模拟,3种策略分别是选择“最近”“最中心”和“最外围”的个体。在虚拟环境中模拟单个捕食者攻击鱼群这一过程,对3种目标选择策略做比较分析,以鱼群结构变化程度的3个关键参数做评判标准。首先发现采用选择“最外围”个体的策略对于中等规模鱼群造成的结构变化程度最大,其次拓展到不同大小规模的鱼群,此策略仍是最有效的,其中小规模鱼群因应对风险能力低,无法体现三种策略的区别。     

Potential biological removal and other currently used management rules for marine mammal populations: A comparison

The management of marine mammal populations requires the balancing of conflicting interests and also compliance with national legislation and international agreements. These conflicts are intensifying and it is becoming urgent that management goals, and justifications, are clear and explicit. This paper summarises six methods currently used to assess the status of marine mammal populations: the IUCN Red List Criteria; the regulations under the European Union Habitats Directive; PBR; the IWC's Revised Management Procedure; HELCOM's approach to managing seals; and the Canadian Objective-Based Fisheries Management system for harp seals. It compares the assumptions and implications of the methods then describes how one of them, PBR, can be re-presented to make explicit the subjective choice at its centre, and push the decision about conservation targets back from scientists to policymakers, where it belongs.     

基于形状特征的XBT探头检测与识别研究

为改进国产投弃式温深仪(XBT)的下降速率公式,拟采用基于图像处理的方法测量其下落过程中的运动参数并分析,为此要实现XBT探头的自动提取。为实现视频图像中XBT探头的自动检测识别,提出了一种基于形状特征的目标检测识别算法。首先通过背景差分法去除背景噪声并阈值分割,采用连通区域的标记算子将二值图像标记为互不连通的待识别区域。然后提取连通区域的偏心率、致密性以及标记图构造描述目标的特征向量,通过计算各连通区域的特征评价函数,利用模糊综合评价方法识别XBT探头。最后对研究方法进行了物理实验验证。实验结果表明:用模糊综合评价方法能较好地在复杂背景下实现目标的识别,能够有效地在序列图像中准确的检测识别出XBT探头目标,为XBT运动参数的测量打下了基础。     

基于递归定量分析的实测海杂波中的小目标检测

提高海杂波中小目标的检测能力,在海洋监视、军事侦察和浮冰检测等军事、民用领域中有着广泛需求,因此海杂波的研究一直是雷达技术领域研究的热点问题。首次将递归定量分析方法引入实测海杂波数据分析中,采用该方法计算海杂波时间序列相空间重构后各递归参量并将其应用于海杂波背景下小目标检测,得到了较好的结果。实验初步证明了采用递归定量分析方法对海杂波数据进行分析和小目标检测是可行并且有效的。