共查询到20条相似文献，搜索用时 46 毫秒
1.
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
2.
Christof Müller 《Marine Geophysical Researches》2005,26(2-4):197-206
Between 1997 and 1999 several marine seismic surveys were carried out in Kiel Bay aimed towards the development of a three-dimensional
acquisition and interpretation technique for small scale subsurface structures using high-frequency sources and multichannel
streamers. The data set was recently revisited by the author and reprocessed to obtain a multichannel stacked seismic data
cube. Nominal hydrophone positions are deduced by determining offsets from first arrival times and estimating the hydrophone
positions under consideration of the ships track. Processing towards a ‘seismic cube’ mainly comprised CMP sorting, constant
velocity NMO correction and stacking. The resulting VHR 3-D seismic ‘brute stack cube’ reveals rich structural details. The
fluvial Pleistocene channel system already documented in an earlier publication was tracked further to the north. It is situated
below a flat cover of gas-bearing Holocene sediments, which locally constitute the seafloor. This till-horizon is superimposed
on a second till layer showing strong topographic variations. Seismic signal phase and shielding effects indicate the possible
presence of gas in these formations. This case history demonstrates that the VHR 3-D seismic method is a feasible tool for
low budget investigation and research. 相似文献
3.
T. Marsset B. Marsset S. Ker Y. Thomas Y. Le Gall 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):628-637
We present the technological development and initial results from the deep-towed seismic acquisition device SYstème SIsmique Fond de mer (SYSIF) recently built by Ifremer. The two configurations of the SYSIF are presented (high resolution (HR): 250–1000 Hz and very high resolution (VHR): 650–2000 Hz), and results are compared to conventional seismic acquisition systems such as multi-channel HR or single-channel VHR (hull-mounted sub-bottom profiler). The ability of SYSIF to achieve higher resolution imagery is due to both the technology employed (low-frequency Janus–Helmoltz piezoelectric transducer) and the deep-towed operating mode (reduction in the Fresnel zone). Sea trials have been conducted in various geological environments and in water depths as deep as 2500 m. The new technique improved imaging of deep seafloor and sub-surface features such as pockmarks, carbonate mounds, sub-marine slides and sub-surface faulting. SYSIF, therefore, is a well-suited tool to investigate deep water geological features, especially those related to geohazard for scientific and industrial purposes. 相似文献
4.
High resolution (HR – sparker) and very high resolution (VHR – boomer) seismic reflection data acquired in shallow water environments
of the Roussillon coastal area are integrated to provide an accurate image of the stratigraphic architecture of the Quaternary
deposits. The complementary use of the two systems is shown to be of benefit for studies of shallow water environments. The
HR sparker data improved the landward part of a general model of Quaternary stratigraphy previously established offshore.
They document an incised valley complex interpreted as the record of successive late Quaternary relative sea-level cycles.
The complex is capped by a polygenetic erosional surface developed during the last glacial period (>18 ky) and variably reworked
by wave ravinement during the subsequent post-glacial transgression. The overlying transgressive systems tract is partly preserved
and presents a varying configuration along the Roussillon coastal plain. The VHR boomer data provide information on the architecture
of the uppermost deposits, both in the near-shore area and in the lagoon. These deposits overlie a maximum flooding surface
at the top of the transgressive systems tract and constitute a highstand systems tract composed of two different architectural
elements. In the near-shore area, a sandy coastal wedge is subdivided into a lower unit and an upper unit in equilibrium with
present day dynamics. In the Salses-Leucate lagoon area, the sedimentary architecture is highly complex due to the closure
of a former embayment and the formation of the present beach barrier. 相似文献
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7.
Development of a System for 3D High-resolution Seismic Reflection Profiling on Lakes 总被引：2，自引：0，他引：2
A high-resolution three-dimensional (3D) seismic reflection system for small-scale targets in lacustrine settings has been
developed. Its main characteristics include navigation and shot-triggering software that fires the seismic source at regular
distance intervals (max. error of 0.25 m) with real-time control on navigation using differential GPS (Global Positioning
System). Receiver positions are accurately calculated (error<0.20 m) with the aid of GPS antennas attached to the end of each
of three 24-channel streamers. Two telescopic booms hold the streamers at a distance of 7.5 m from each other. With a receiver
spacing of 2.5 m, the bin dimension is 1.25 m in inline and 3.75 m in crossline direction. To test the system, we conducted
a 3D survey of about 1 km2 in Lake Geneva, Switzerland, over a complex fault zone. A 5-m shot spacing resulted in a nominal fold of 6. A double-chamber
bubble-cancelling 15/15 in3 air gun (40–650 Hz) operated at 80 bars and 1 m depth gave a signal penetration of 300 m below water bottom and a best vertical
resolution of 1.1 m. Processing followed a conventional scheme, but had to be adapted to the high sampling rates, and our
unconventional navigation data needed conversion to industry standards. The high-quality data enabled us to construct maps
of seismic horizons and fault surfaces in three dimensions. The system proves to be well adapted to investigate complex structures
by providing non-aliased images of reflectors with dips up to 30°. 相似文献
8.
High Resolution (220–1050 Hz) seismic acquisition performed in deep water using deep-towed systems provides unrivalled lateral resolution when compared to conventional surface seismic. The lateral resolution of these acquisitions is controlled by the width of the first Fresnel zone, taking advantage of their positions close to the sea bottom. No current existing deep towed equipment can benefit from seismic imaging processing techniques to improve this resolution as a consequence of positioning inaccuracies. The technological developments of a digital deep-towed multichannel streamer are presented with a particular attention to positioning: each hydrophone incorporates a pitch, roll and heading sensor in order to monitor the constant deformation of the streamer in operation. The sea trials took place in July 2013 in the Mediterranean Sea. Pre-stack depth migration applied to the deep-towed multichannel data illustrates the potential of this emerging methodology in terms of penetration (12 dB improvement in Signal/Noise) and lateral resolution (mean signal wavelength: 3 m) when compared with deep-towed single-channel acquisition. 相似文献
9.
Dhananjai Pandey Martin Sinha Lucy MacGregor Satish Singh 《Marine Geophysical Researches》2008,29(3):185-193
The effects of the ocean coast on magnetotelluric (MT) data have been studied and results are described in this article. MT
soundings from various sites along coastal plains of Kachchh were acquired where volcanic rocks overlie Mesozoic sediments
having potential resource prospects. The region of our study lies in the proximity of Gulf of Kachchh and Arabian Sea. This
article describes the effects the presence of a conductive body on the acquired MT data. With the help of synthetic MT modelling
and induction arrows we demonstrate the influence of shallow conductive body on the MT data. The modelling results when compared
to the field observations show that much of the high frequencies are unaffected by the coast, however low frequencies of the
data do seem to be distorted by onshore–offshore resistivity contrasts. The least affect on high frequencies can be attributed
to very shallow water depth as well as to the fact that the onshore–offshore resistivity contrasts are not large enough to
influence the high frequency data badly. The results presented here report for the first time the effect of the coast on the
analysis on MT data from Kachchh. Due to several academic as well as industrial onshore–offshore MT experiments presently
being carried out to explore its hydrocarbon potential, our results have an important bearing on designing and acquisition
of future MT surveys in this region. 相似文献
10.
基于ROV的近海底地形测量及其在马努斯盆地热液区的应用 总被引：3，自引：0，他引：3
针对重点的特殊深海研究区（如热液冷泉、洋中脊区域）,在船载多波束数据获得研究区大面积地形资料的基础上,有必要选取典型深海小靶区进行高分辨率地形测量为进一步深入研究提供保障。根据船载多波束实测数据选取PACMANUS热液区作为靶区,基于长基线定位,利用“发现”ROV搭载多波束系统进行近海底全覆盖地形测量。结果表明,依托于船动力定位系统及差分GPS,长基线为ROV提供了可靠的高精度定位,使得近海底测量的地形数据分辨率数倍优于船载多波束测得的地形数据的分辨率。高分辨率地形清晰的显示了PACMANUS热液区锥形丘体等特殊微地形,与已发现的热液点和火山区有很好的对应。进一步分析发现,该区域活动的热液区主要发育于坡度大于30°斜坡上的地形突变区,其成因仍需深入研究。利用ROV搭载多波束近底测量是获取深海小靶区高分辨率地形的可靠途径和方法,有利于提高深海海底研究的针对性,将促进我国深海科学研究的发展。 相似文献
11.
针对水下目标图像探测一直是困扰海洋界的1个难题，进行了水下探测的线扫描系统的设计和相关试验。从实验结果来看，线扫描系统可以很好地描述水下物体的三维外形细节，对于水下目标探测、识别十分有效。 相似文献
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13.
This chapter describes two separate but complementary research echosounder systems originally developed by Krupp Atlas Elektronik GmbH for the new German oceanographic research vessel Meteor.The Hydrosweep is a Hydrographic wide-swathe sweep survey echosounder for both shallow and deep water applications providing accurate bathymetric surveys and terrain-following navigation capabilities.The Parasound system is a hull-mounted dual channel parametric narrow-beam deep sea survey and sub-bottom profiling echosounder enabling particularly high vertical and horizontal resolution of seabed features. 相似文献
14.
在过去的十几年中,海洋可控源电磁法的迅猛发展在油气勘探中起到了重要的作用。在浅海环境中,常见的两种可控源电磁法的数据采集系统采用海底基站式（Sea Bed Logging（SBL））,以及拖缆式（Towed Streamer electromagnetics（TSEM））两种模式。本文的研究目的是研究在不同水深条件下,两种数据采集系统的工作模式以及海水对其的影响。为了更好的比较两种数据采集方式,本文采用了三种不同的分析方法：一维敏感度模型,二维油藏敏感指数,Occam反演。一维敏感度模型能够迅速的给出结果,但是由于结果的信息量有限,不足以给定准确的结论。二维油藏敏感指数可以依据正演的结果快速的给定一个水深和油藏敏感度的关系。Occam反演方法用于对合成数据进行反演计算,估计地下介质电阻率参数。为了更好的评价反演结果,本文引入了横向电阻异常率（ATR）。通过对合成数据的反演结果的分析,本文得出以下结论：在浅水环境中,SBL和TSEM数据采集系统都可以提供较高的分辨率,对高电阻层有很好的敏感度。在深水环境中,SBL数据采集系统具有明显的优势。ATR对于反演的电阻率参数结果具有很好的评价作用。 相似文献
15.
Shallow water depth retrieval from space-borne SAR imagery 总被引：1，自引：1，他引：0
Kaiguo Fan Weigen Huang Hui Lin Jiayi Pan Bin Fu Yanzhen Gu 《Journal of Oceanography》2011,67(4):405-413
Based on shallow water bathymetry synthetic aperture radar (SAR) imaging mechanism and the microwave scattering imaging model
for oceanic surface features, we developed a new method for shallow water depth retrieval from space-borne SAR images. The
first guess of surface currents and winds are estimated from the normalized radar crossing section (NRCS) profile of shallow
water bathymetry SAR imagery, according to the linear theory and geophysical model function. The NRCS profile is then simulated
by the microwave scattering imaging model. Both the surface currents and winds are adjusted by using the dichotomy method
step by step to make the M4S-simulated NRCS profiles approach those observed by SAR. Then, the surface currents and the wind
speeds are retrieved when a best fit between simulated signals and the SAR image appears. Finally, water depths are derived
using the Navier–Stokes equation and finite difference method with the best estimated currents and the surface winds. The
method is tested on two SAR images of the Taiwan Shoal. Results show that the simulated shallow water NRCS profile is in good
agreement with those measured by SAR with the correlation coefficient as high as 85%. In addition, when water depths retrieved
from the SAR image are compared with in situ measurements, both the root mean square and relative error are less than 3.0 m
and 6.5%, respectively, indicating that SAR images are useful for shallow water depth retrieval and suggesting that the proposed
method in this paper is convergent and applicable. 相似文献
16.
Within a shipyard, many designers each have their own design objective cooperating in complex design circumstance that a variety of software tools run on different hardware platforms. Different CAD systems are used by different design stages and departments, and the design result is usually delivered on paper drawings. The proliferation of data and the rising number of disparate data systems do not communicate with each other and certainly do not collaborate. Advanced 3D modelling tools are installed in most of progressive shipyards for advantage to improve their productivities. However these 3D models are repetitiously constructed as per the specified design objectives of disparate software tools in various design stages. This paper describes the development of collaboration modelling framework, knowledge-based design support system, to make a web-based data-sharing collaborative environment potentially allowing to facilitate some applications, construct 3D lines rapidly, translate the product data, and further be capable of providing reasonable model configurations for XML type, and sharing the web services from the Internet to comply with shipyards’ specific strategy for each particular case to be designed. 相似文献
17.
Carl Jörg Petersen Stefan Bünz Steinar Hustoft Jürgen Mienert Dirk Klaeschen 《Marine and Petroleum Geology》2010
The newly developed P-Cable 3D seismic system allows for high-resolution seismic imaging to characterize upper geosphere geological features focusing on geofluid expressions (gas chimneys), shallow gas and gas hydrate reservoirs. Seismic imaging of a geofluid system of an Arctic sediment drift at the Vestnesa Ridge, offshore western Svalbard, provides significantly improved details of internal chimney structures from the seafloor to ∼500 m bsf (below seafloor). The chimneys connect to pockmarks at the seafloor and indicate focused fluid flow through gas hydrated sediments. The pockmarks are not buried and align at the ridge-crest pointing to recent, topography-controlled fluid discharge. Chimneys are fuelled by sources beneath the base of gas hydrate stability zone (GHSZ) that is evident at ∼160–170 m bsf as indicated by a bottom-simulating reflector (BSR). Conduit centres that are not vertically straight but shift laterally by up to 200 m as well as discontinuous internal chimney reflections indicate heterogeneous hydraulic fracturing of the sediments. Episodically active, pressure-driven focused fluid flow could explain the hydro-fracturing processes that control the plumbing system and lead to extensive pockmark formation at crest of the Vestnesa Ridge. High-amplitude anomalies in the upper 50 m of the chimney structures suggest formations of near-surface gas hydrates and/or authigenic carbonate precipitation. Acoustic anomalies, expressed as high amplitudes and amplitude blanking, are irregularly distributed throughout the deeper parts of the chimneys and provide evidence for the variability of hydrate and/or carbonate formation in space and time. 相似文献
18.
The hydrodynamic performance of the oscillating water column type shoreline-mounted wave-power device is numerically studied within linear wave theory by using a boundary element method based on the Wehausen and Laitone 3D shallow water Green's function. In order to verify the numerical model, a 1:12 physical model with different bottom slopes was constructed and tested in a wave basin under regular wave conditions. The effects of the bottom slope on the hydrodynamic performance are investigated by both analytical and experimental methods. 相似文献
19.
Larry A. Mayer 《Marine Geophysical Researches》2006,27(1):7-17
Over the past few years there have been remarkable and concomitant advances in sonar technology, positioning capabilities,
and computer processing power that have revolutionized the mapping, imaging and exploration of the seafloor. Future developments
must involve all aspects of the “seafloor mapping system,” including, sonars, ancillary sensors (motion sensors, positioning
systems, and sound speed sensors), platforms upon which they are mounted, and the products that are produced. Current trends
in sonar development involve the use of innovative new transducer materials and the application of sophisticated processing
techniques including focusing algorithms that dynamically compensate for the curvature of the wavefront in the nearfield and
thus allow narrower beam widths (higher lateral resolution) at close ranges . Future developments will involve “hybrid”, phase-comparison/beam-forming
sonars, the development of broad-band “chirp” multibeam sonars, and perhaps synthetic aperture multibeam sonars. The inability
to monitor the fine-scale spatial and temporal variability of the sound speed structure of the water column is often a limiting
factor in the production of accurate maps of the seafloor; improvements in this area will involve continuous monitoring devices
as well as improved ocean models and perhaps tomography. Remotely Operated Vehicles (ROV’s) and particularly Autonomous Underwater
Vehicles (AUV’s) will become more important as platforms for seafloor mapping systems. There will also be great changes in
the products produced from seafloor mapping and the processing necessary to create them. New processing algorithms are being
developed that take advantage of the density of multibeam sonar data and use statistically robust techniques to “clean” massive
data sets very rapidly. A range of approaches are being explored to use multibeam sonar bathymetry and imagery to extract
quantitative information about seafloor properties, including those relevant to fisheries habitat. The density of these data
also enable the use of interactive 3-D visualization and exploration tools specifically designed to facilitate the interpretation
and analysis of very large, complex, multi-component spatial data sets. If properly georeferenced and treated, these complex
data sets can be presented in a natural and intuitive manner that allows the simple integration and fusion of multiple components
without compromise to the quantitative aspects of the data and opens up new worlds of interactive exploration to a multitude
of users. 相似文献
20.
Quasi-3D Numerical Simulation of Tidal Hydrodynamic Field 总被引：2，自引：0，他引：2
SONG Zhiyao XUE Hongchao YAN Yixin MAO Lihua XU Fumin
Doctor Senior Engineer College of Harbor Waterway Coastal Engineering Hohai University 《中国海洋工程》1999,(3)
Based on the 2D horizontal plane numerical model,a quasi-3D numerical model is establishedfor coastal regions of shallow water.The characteristics of this model are that the velocity profiles can be ob-tained at the same time when the equations of the value of difference between the horizontal current velocityand its depth-averaged velocity in the vertical direction are solved and the results obtained are consistent withthe results of the 2D model.The circulating flow in the rectangular area induced by wind is simulated and ap-plied to the tidal flow field of the radial sandbanks in the South Yellow Sea.The computational results fromthis quasi-3D model are in good agreement with analytical results and observed data.The solution of the finitedifference equations has been found to be stable,and the model is simple,effective and practical. 相似文献