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41.
Jonathan M. Bull Martin Gutowski Justin K. Dix Timothy J. Henstock Peter Hogarth Timothy G. Leighton Paul R. White 《Marine Geophysical Researches》2005,26(2-4):157-169
Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1–24 kHz) to produce
decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp
system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and
precise positioning of sources and receivers. Full 3D numerical modelling of the combined source and receiver directivity
was completed to determine optimal source and receiver geometries. The design incorporates four source transducers (1.5–13 kHz)
that can be arranged into different configurations, including Maltese Cross, a square and two separated pairs. The receive
array comprises 240 hydrophones in 60 groups whose group-centres are separated by 25 cm in both horizontal directions, with
each hydrophone group containing four individual elements and a pre-amplifier.
After careful consideration, it was concluded that the only way to determine with sufficient accuracy the source–receiver
geometry, was to fix the sources and receivers within a rigid array. Positional information for the array is given by a Real
Time Kinematic GPS and attitude system incorporating four antennas to give position, heading, pitch and roll. It is shown
that this system offers vertical positioning accuracy with a root-mean-square (rms) error less than 2.6 cm, while the horizontal
positioning rms error was less than 2.0 cm. The system is configured so that the Chirp source signature can be chosen by software
aboard the acquisition vessel.
The complete system is described and initial navigational and seismic data results are presented. These data demonstrate that
the approach of using fixed source-receiver geometry combined with RTK navigation can provide complete 3D imaging of the sub-surface. 相似文献
42.
Particularly Sensitive Sea Areas (PSSAs) are a tool designed to protect vulnerable marine areas from vessel-source pollution through measures approved by the governing body, the International Maritime Organisation. Recent developments triggered by the proposal to designate, amongst others, a large part of the Western European Atlantic a PSSA have brought the instrument to a decisive stage. Although the proposal appears to be lawful, its implications for the concept, which this paper seeks to assess, are questionable. The significance of the instrument is at risk if it is overused. As a consequence, new protective mechanisms should be contemplated. 相似文献
43.
由于海岸带的地理条件和海洋动力特性的复杂性以及人类开发活动对海岸带的影响,近岸海域的生态环境系统在空间分布上有很大的变异性.基于现场实测资料,建立系统的空间变异分析模型,对海岸带生态环境空间变化规律进行分析,可以充分了解不同区域的污染特征和变化趋势.应用所构建的空间变异分析模型对渤海湾天津近岸海域的水环境特性进行分析,结合对应年份的入海流量及其变化,分析了天津渤海湾海岸带污染的主因子和区域水环境的分布特征,结果可以对海洋功能区的划分和水环境综合评价结果进行验证和补充. 相似文献
44.
45.
46.
气相色谱指纹法在海上油污染源鉴别中的应用 总被引:4,自引:0,他引:4
通过一个具体案例,探讨了气相色谱指纹法在海上油污染源鉴别中的应用。该鉴别方法基于样品的正构烷烃气相色谱指纹分析,选择既能表征油种固有特性,又受风化影响较小的正十七烷(n-C17)、正十八烷(n-C18)、姥鲛烷(phy)、植烷(phy)和正二十烷(n-C20)等特征烷烃作为判据,可信度大,而且整个操作流程短(一般不超过半天),较简便易行。 相似文献
47.
本文综述了国内外酸雨的研究现状;包括酸雨的来源、成因、模式、影响及防治对策;介绍了酸雨的研究趋势;并着重就厦门地区今后酸雨的研究方向提出也作者的看法。 相似文献
48.
在洋浦近岸海域计算潮流场基础上,计算预选排污口附近海水质点运动轨迹及预测污染物浓度分布,最后,从环保角度出发,推荐了洋浦地区各开发区的排污口位置,为洋浦近岸海域污染控制规划方案的制定及其优化提供了依据。 相似文献
49.
叶立勋 《中国海洋大学学报(自然科学版)》1990,(3)
介绍三种通过底栖动物群落结构的变化对有机物污染监测和评价的方法,并分别对澳大利亚塔斯马尼亚州Nubeena鳟鱼养殖场内由高密度网箱养鱼诱发的有机物污染进行了检测。结果表明:距网箱垂线0m处为严重污染区域,10m处为中度污染区域,30m为过渡类型,其有机物对该处底栖生物仍具有害影响,60m处为轻度有机物富集区,但该处有机物对底栖生物的总效应是有益的,60m以外为正常区域。本文还对三种方法的适用性进行了讨论。 相似文献
50.
Calculating Pollution Indices by Heavy Metals in Ecological Geochemistry Assessment and a Case Study in Parks of Beijing 总被引:4,自引:0,他引:4
Pollution index is a powerful tool for ecological geochemistry assessment. The commonly used pollution indices by heavy metals in soils and sediments were classified as two types of single index and integrated index in an algorithm point of view. Four single indices of contamination factor (or concentration factor), ecological risk factor, enrichment factor, and index of geo-accumulation were illustrated, and the reference values for calculating single indices were distinguished into background levels and threshold pollution values. Eight integrated indices were divided into two groups. One group is suitable for the normal distribution single indices including the sum, average, weighted average,vector modulus, and Nemerow pollution indices, and the other for log-normal distribution including the product, root of product, and weighted power product pollution indices. Using background levels as reference values, five contamination classes were divided, and the terminologies are suggested for the single and integrated indices to unify the assessment results. Software of EGAPI was developed in a single document interface to calculate the four single and eight integrated indices by heavy metals to assess the quality of soil and sediment ecological geochemistry. Pollution indices by heavy metals of Cu,Pb, and Zn in soils in parks of Beijing were calculated using EGAPI software, and these five contamination classes and terminologies suggested in this study were evaluated and used. Results ofintegrated indices of Cu, Pb, and Zn in soils indicated that the soil qualities are unpolluted as a whole and varied from low polluted to unpolluted status from the center to the outskirts of Beijing City. 相似文献