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161.
162.
The Eastern Mediterranean Sea is a remnant of a deep Mesozoic oceanic basin, now almost totally consumed as a result of long-term
plate convergence between Eurasia and Africa. The present-day surface morphology of the Eastern Mediterranean relates both
to the early history of formation of the deep basins and the recent geodynamic interactions between interfering microplates.
Among the most conspicuous morphologic features of the basin is an arc-shape, elongated and wide, bathymetric swell bisecting
the entire basin from the Ionian to Levantine areas, known as the Mediterranean Ridge. During the last decade this tectono-sedimentary
accretionary prism, which results from the Hellenic subduction, has been intensively surveyed by swath mapping, multichannel
seismic profiling and deep dives. We present here, and briefly discuss, the main morphological characteristics of this feature
as derived from swath bathymetric data that considerably help to better assess the lateral and north–south morphostructural
variability of the Mediterranean Ridge. This study reveals that the characteristics and morphostructural variability of the
Mediterranean Ridge are related to: (1) a specific incipient collision geodynamic setting south of Crete, where the African
and Aegean continental margins are nearly in contact, (2) a unique regional kinematics, controlled by frontal convergence
south of Crete (central Mediterranean Ridge) and oblique subduction with opposite sense of shear for the western (Ionian)
and eastern (Levantine) domains of the Mediterranean Ridge, that explain the lateral variations of deformation and (3) particularities
of its sedimentary cover, which includes massive salt layers within the outer Mediterranean Ridge and local salt deposits
within the inner domains, that control the north–south morphostructural variability of the sedimentary wedge. 相似文献
163.
Processing and analysis of Simrad multibeam sonar data 总被引:1,自引:0,他引:1
Neil C. Mitchell 《Marine Geophysical Researches》1996,18(6):729-739
The common approach to analysing data collected with multibeam and sidescan sonars is to visually interpret charts of contoured bathymetry and mosaics of seabed images. However, some of the information content is lost by processing the data into charts because this involves some averaging; the analysis might uncover more information if done on the data at an earlier stage in the processing. Motivated by this potential, I have created a software system which can be used to analyse data collected with Simrad EM1000 (shallow water) and EM12 (deep water) multibeam sonars, as well as to generate bathymetry contour charts and backscatter mosaics. The system includes data preprocessing, such as navigation filtering, depth filtering (removal of outlying values), and amplitude mapping using the multibeam bathymetry to correctly position image pixels across the swath. The data attributes that can be analysed include the orientation and slope of the seafloor, and the mean signal strength for each sounding. To determine bathymetry attributes such as slope, the soundings across a number of beams and across a series of pings are grouped and a least-squares plane fitted to them. Bathymetric curvature is obtained by detrending the grouped data using the least-squares plane and fitting a paraboloid to the residuals. The magnitudes and signs of the paraboloid's coefficients reveal depressions and hills and their orientations. Furthermore, the seafloor geology can be classified using a simple combination of these attributes. For example, flat-lying sediments can be classified where the backscatter, slope and curvature fall below specified values. 相似文献
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166.
随着含溴阻燃剂的进一步限用或禁用,氯代阻燃剂得克隆(Dechlorane Plus, DP)以其良好的热稳定性和电化学性能成为推荐的替代品之一。作为添加型氯代阻燃剂,DP很容易从产品中脱落而成为环境中广泛存在的污染物,但相关的研究仍十分匮乏。本研究测定了杭州湾海域4个底泥柱状样品中DP的残留及异构体特征,并对DP在该海域底泥中的时空分布和可能来源进行了初步分析。结果表明,syn-DP和anti-DP在底泥样品中的含量分别为BDL~17.7 pg/g干质量(平均为2.9±3.2 pg/g干质量)和1.4~38.1 pg/g 干质量(平均为8.0±8.5 pg/g干质量),其污染程度相对全球范围处于较低水平。空间分布表明金山工业区可能对杭州湾DP的污染有一定贡献,DP在柱状底泥中的垂直分布未发现明显变化趋势。本研究中DP的fsyn平均值为0.25~0.28,表明研究海域底泥中的DP可能来自于远距离传输。 相似文献
167.
168.
多波束与侧扫声纳海底目标探测的比较分析 总被引:2,自引:0,他引:2
侧扫声纳是目前常用的海底目标(如沉船、水雷、管线等)探测工具,在测深领域,多波束以全覆盖和高效率证明了它的优越性。由于多波束具有很高的分辨率,目前在工程上已经开始应用多波束进行海底目标物的探测。对多波束和侧扫声纳进行了比较分析,并着重探讨了影响多波束分辨率的各种因素。结果表明:多波束的最大优点在于定位精度高,但其适用范围不如侧扫声纳广泛,尤其受到水深和波束角的限制,多波束和侧扫声纳在探测海底目标时具有很好的互补性,同时应用可以提高目标解译的准确性。 相似文献
169.
170.
Length scales and statistical characteristics of outer bank roughness for large elongate meander bends: The influence of bank material properties,floodplain vegetation and flow inundation 下载免费PDF全文
Kory Konsoer Bruce Rhoads James Best Eddy Langendoen Mick Ursic Jorge Abad Marcelo Garcia 《地球表面变化过程与地形》2017,42(13):2024-2037
This article explores the length scales and statistical characteristics of form roughness along the outer banks of two elongate bends on a large meandering river through investigation of topographic variability of the bank face. The analysis also examines how roughness varies over the vertical height of the banks and when the banks are exposed subaerially and inundated during flood stage. Detailed data on the topography of the outer banks were obtained subaerially using terrestrial LiDAR during low flow conditions and subaqueously using multibeam echo sounding (MBES) during near‐bankfull conditions. The contributions of various length scales of topographic irregularity to roughness for subaerial conditions were evaluated for different elevation contours on the bank faces using Hilbert–Huang Transform (HHT) spectral analysis. Statistical characteristics for discrete areas on the bank faces were determined by calculating the root‐mean‐square of normal distances from a triangulated irregular network (TIN) surface. Results of the HHT analysis show that the characteristics of roughness along bank faces composed primarily of non‐cohesive sediment, and eroding into cropland, vary with bank elevation and exhibit a dominant range of roughness length scales (~15–50 m). However, bank faces composed predominantly of cohesive material and carved into a forested floodplain have relatively uniform topographic roughness characteristics over the vertical extent of the bank face and do not exhibit a dominant roughness length scale or range of length scales. Additionally, comparison between local surface roughness for subaerial versus subaqueous conditions shows that roughness decreases considerably when the banks are submerged, most likely because of the removal of vegetation and eradication of small‐scale erosional features in non‐cohesive bank materials by flow along the bank face. Thus, roughness appears to be linked to the hydraulic conditions affecting the bank, at least relative to conditions that develop when banks are exposed subaerially. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献