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21.
Michael Riedel 《Marine Geophysical Researches》2007,28(4):355-371
Two single-channel seismic (SCS) data sets collected in 2000 and 2005 were used for a four-dimensional (4D) time-lapse analysis
of an active cold vent (Bullseye Vent). The data set acquired in 2000 serves as a reference in the applied processing sequence.
The 4D processing sequence utilizes time- and phase-matching, gain adjustments and shaping filters to transform the 2005 data
set so that it is most comparable to the conditions under which the 2000 data were acquired. The cold vent is characterized
by seismic blanking, which is a result of the presence of gas hydrate in the subsurface either within coarser-grained turbidite
sands or in fractures, as well as free gas trapped in these fracture systems. The area of blanking was defined using the seismic
attributes instantaneous amplitude and similarity. Several areas were identified where blanking was reduced in 2005 relative
to 2000. But most of the centre of Bullseye Vent and the area around it were seen to be characterized by intensified blanking
in 2005. Tracing these areas of intensified blanking through the three-dimensional (3D) seismic volume defined several apparent
new flow pathways that were not seen in the 2000 data, which are interpreted as newly generated fractures/faults for upward
fluid migration. Intensified blanking is interpreted as a result of new formation of gas hydrate in the subsurface along new
fracture pathways. Areas with reduced blanking may be zones where formerly plugged fractures that had trapped some free gas
may have been opened and free gas was liberated. 相似文献
22.
Moo Hee Kang Hyun-Chul Han Hyesu Yun Gee Soo Kong Kyong O. Kim Youn Soo Lee 《Marine Geophysical Researches》2007,28(3):257-269
A seamount chain with an approximately WNW trend is observed in the northeastern Ulleung Basin. It has been argued that these
seamounts, including two islands called Ulleung and Dok islands, were formed by a hotspot process or by ridge related volcanism.
Many geological and geophysical studies have been done for all the seamounts and islands in the chain except Anyongbok Seamount,
which is close to the proposed spreading ridge. We first report morphological characteristics, sediment distribution patterns,
and the crustal thickness of Anyongbok Seamount using multibeam bathymetry data, seismic reflection profiles, and 3D gravity
modeling. The morphology of Anyongbok Seamount shows a cone shaped feature and is characterized by the development of many
flank cones and flank rift zones. The estimated surface volume is about 60 km3, and implies that the seamount is smaller than the other seamounts in the chain. No sediments have been observed on the seamount
except the lower slope, which is covered by more than 1,000 m of strata. The crustal structure obtained from a 3D gravity
modeling (GFR = 3.11, SD 3.82 = mGal) suggests that the seamount was formed around the boundary of the Ulleung Plateau and
the Ulleung Basin, and the estimated crustal thickness is about 20 km, which is a little thicker than other nearby seamounts
distributed along the northeastern boundary of the Ulleung Basin. This significant crustal thickness also implies that Anyongbok
Seamount might not be related to ridge volcanism. 相似文献
23.
24.
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
25.
合浦珠母贝二倍体、三倍体和非整倍体群体的基因杂合度与生长比较 总被引:6,自引:0,他引:6
采用淀粉凝胶电泳方法对合浦珠母贝Pinctadamartensi(D.)雌性三倍体与雄性二倍体交配,细胞松弛素B抑制其受精卵第一极体释放产生的二倍体、三倍体及非整倍体3个群体进行了同工酶研究。二倍体、三倍体及非整倍体群体在6个多态位点的平均基因杂合度分别为0.255±0.087,0.286±0.097,0.275±0.089,三倍体的杂合度高出二倍体约12%,表明多倍体诱导能增加诱导群体的杂合度。但在单个位点上,三倍体的杂合度不一定高于二倍体;在各自群体内,平均杂合位点数与生长间无明显的相关性,单个位点上的杂合子也未完全表现出其生长大于纯合子,且差异不明显(p>0.05)。因此,合浦珠母贝三倍体的快速生长难以完全用杂合度增高假说解释,只能说明诱导处理能使三倍体的杂合度增高,而能量再分配和"巨型性"可能对其快速生长起着不可忽视的作用。非整倍体群体的杂合度高于二倍体群体,但其生长却小于二倍体,其原因可能是染色体的增减对机体的生长有一定的影响。 相似文献
26.
27.
LIANGDong-fang CHENGLiang KervinYEOW 《中国海洋工程》2005,19(2):269-286
A numerical model for the self-burial of a pipeline trench is developed. Morphological evolutions of a pipeline trench under steady-current or oscillatory-flow conditions are simulated with/without a pipeline inside the trench. The oscillatory flow in this study represents the action of waves. The two-dimensional Reynolds-averaged continuity and Navier-Stokes equations with the standard k-e turbulence closure, as well as the sediment transport equations, are solved with the finite difference method in a eurvilirrear coordinate system. Both bed and suspended loads of sediment transport are included in the morphological model. Because of the lack of experimental data on the backfilling of pipeline trenches, the numericalmodel is firstly verified against three closely-relevant experiments available in literature. A detailed measurement of the channel migration phenomenon under steady currents is employed for the assessment of the integral performance of themodel. The two experimental results from U-tube tests are used to validate the model‘s ability in predicting oscillatory flows. Different time-marching schemes are employed for the morphological computation under unidirectional and oscillatory conditions. It is found that vortex motions within the trench play an important role in the trench development. 相似文献
28.
29.
北京市基础测绘技术规程的探讨 总被引:1,自引:1,他引:0
分析了规程与现行相关法律、法规和标准的关系,探讨了北京市基础测绘技术规程的内容,介绍了其创新点和应用情况。通过分析介绍,该地方标准统一了北京市基础测绘的技术标准,规范了基础测绘成果,有利于实现测绘信息资源的共享和有效利用。 相似文献
30.
风云卫星遥感数据高精度地理定位软件系统开发研究 总被引:1,自引:0,他引:1
为了适应风云气象卫星遥感数据高精度地理定位要求,在研究和比较分析现有环境气象卫星遥感数据地理定位方法,尤其对其中关键的轨道计算模型进行对比研究之后,我们使用变阶变步长多步卫星轨道数值计算模型(DE/DEABM)进行气象卫星轨道计算,研制开发了新一代卫星轨道计算及遥感数据地理定位软件系统.该软件系统中卫星轨道数值积分计算模型包含了多项摄动因素计算,特别是对低轨卫星影响较大的因素,其中地球的球形引力项使用了高精度高阶EGM-96地球引力场模型,提高了非球形引力摄动计算精度,另外还考虑了太阳、月亮引力项,辐射光压摄动和大气摄动因素,使得轨道计算精度大大提高.在遥感数据定位算法开发工作中,以中国2002年5月发射的风云1号D星10通道扫描辐射计和计划2008年上半年发射的风云3号A卫星中分辨率光谱成像仪等遥感仪器为对象,比较详细地分析和研究了探测器、焦平面、主光学系统和扫描镜等遥感仪器几大关键部件的光学几何关系,提高了坐标转换系统计算精度.经过对风云1号D星多天逐日的轨道计算和定位计算试验,结果表明该软件系统24h风云1号D星轨道计算卫星矢径精度可达到几十厘米至几十米,较原来平根数分析解方法1000m左右精度有显著量级的提高.同时,风云1号D星遥感数据地理定位精度达到星下点1个像元. 相似文献