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601.
在分析锥束CT平板探测器校正方法及环形伪影残留原因的基础上,提出一种简便的基于空气扫描的锥束CT环形伪影校正方法。该方法首先在同一锥束CT系统中采用相同参数进行空气扫描和被测物体扫描,然后分别重建出系列切片图像,最后由被测物体切片图像与空气切片图像对应相减实现残留环形伪影的校正,同时起到一定的降噪作用。实验结果验证了该方法的可行性和有效性。 相似文献
602.
以长江口崇明岛北支潮滩的3个潮滩为对象,在粒度测量和磁性分析的基础上,揭示了现代潮滩表层沉积物的磁性变化,探讨了磁性矿物、尤其是自生亚铁磁性矿物—硫复铁矿(Fe3S4)在潮滩沉积微相的分布规律及机制。研究结果表明:长江口潮滩表层沉积物的磁性特征由亚铁磁性矿物及超顺磁颗粒(SP)主导。淤积型中高潮滩磁铁矿以单畴(SD)和SP为主,侵蚀型潮滩的中低潮滩则更多假单畴/多畴(PSD/MD)晶粒,反映了水动力的分选及以细颗粒矿物溶解为主的早期成岩作用。此外,最东侧的北四滧港剖面潮上带—高潮滩芦苇带普遍存在自生亚铁磁性硫复铁矿,北堡港和新卫剖面的高潮滩也局部存在硫复铁矿,反映了本区高潮滩—潮上带丰富的有机质及细颗粒沉积物、加上有限的海水淹没时间,是早期成岩作用过程中生成硫复铁矿的主要机制。 相似文献
603.
基于影像间潮滩地形修正的海岸线监测研究——以黄河三角洲为例 总被引:6,自引:0,他引:6
针对潮滩环境中潮汐和坡度变化对海岸线变化监测的影响,提出一种通过两景影像计算潮滩坡降进而准确获得海岸线的方法,并利用坡降值估算潮滩体积。以岸线变化较剧烈的黄河三角洲南部的甜水沟口至小清河口的粉砂淤泥质潮滩为例进行应用研究。结合遥感影像、实测固定断面数据和水深测量数据分析表明,影像间的潮差对坡降估算值虽有较大影响,但选择合适潮位估算潮滩坡降是可行的,估算坡降的最小相对误差可达0.2%,均方根误差小于实测坡降一个数量级。1973-2009 年甜水沟口至小清河口14 个年份的岸线变化分析显示,黄河改道对本区的直接淤积影响在甜水沟向南3 km范围内,最大淤积区位于甜水沟口附近,年均淤积率31 m/a,而后在1989-2002 年海区南部出现较大幅度淤积,主要为黄河入海水沙直接或间接淤积造成的;研究时段内岸滩总体演化趋势为蚀退,最大年均蚀退速率51 m/a,黄河改道造成的海洋动力变化是影响本区海岸冲刷的主要因素。验证表明,本文方法计算的潮滩体积用于指示海滩冲淤变迁是合理可行的。 相似文献
604.
潮滩上波高的时空变化及其影响因素——以长江三角洲海岸为例 总被引:1,自引:0,他引:1
于2009—2010年的不同季节在崇明东滩北部、中部、南部以及杭州湾北岸东段的芦潮港岸段,利用目前先进的SBE 26plus浪潮仪进行了多个潮周期的波浪观测。研究表明,观测期间潮周期平均风速为1.9~11.0m/s、最大风速为2.8~12.1m/s,各测点潮周期平均水深为0.28~2.12m,高潮位最大水深为0.37~3.19m,潮周期有效波高为0.03~0.45m,最大波高为0.08~1.59m。波高的时空变化受风速、风向、水深和岸滩坡度的综合影响。通常情况下,向岸风期间的波浪较大;风速、水深、岸滩坡度越大,潮滩上的波高也越大。空间上,岸滩坡度最小的崇明东滩中部(坡度0.6‰)测点波高和水深之间的相关性最好,岸滩坡度最大的芦潮港潮滩(坡度8.7‰)测点两者间的相关性最差。时间上,波高和水深之间的相关性与风速、风向的变化有关。因此,只有在潮滩坡度较小(例如<1‰),风速、风向较为稳定时,波高和水深之间的显著正相关关系才存在。要了解某个潮滩的波浪特征,有必要利用先进的仪器进行系统的原位观测,而非简单地借助其它潮滩的波浪研究结果。研究推断,在向岸强台风和大潮高潮位阶段,崇明东滩中潮线附近的最大波高可达1.5~2.0m,芦潮港堤外潮滩的最大波高可达2m以上。 相似文献
605.
606.
Dredged spoil (DS) was used as a silt and clay additive in the construction of artificial tidal flats from mountain sand (MS). As the ratio of DS in the sediment media increased, the number of emerging macrobenthos increased. The composition of the macrobenthic community was also affected by the addition of DS, and the changes might be dependent on the ratio of DS to MS. In addition, the macrobenthos in the artificial tidal flats was more abundant than that in the control tidal flat, which was constructed with natural tidal flat sediment. With a silt and clay content of 25%, polychaetes Ceratonereis erythraeensis and Capitella sp. and the gastropod Batillaria cumingii were dominant, whereas no bivalves were present. With less silt and clay (5% and 10%), the bivalves Ruditapes philippinarum and Musculista senhousia were observed in the artificial flats, while their numbers in the control tidal flat were lower. 相似文献
607.
608.
Due to their slow growth rates, seamount Co-rich crusts are very difficult to date with high resolution and precision. This
paper is to test the use of orbital pacing on the growth profile of crusts to determine high-resolution age and growth rate.
Crust CB14 from the central Pacific Ocean was selected for this study. We first examined the growth pattern in detail under
a reflected-light microscope and ascertained that the growth environment was stable for the sub-layer 1 (0–3 mm). We then
used electron microprobe line-scanning to obtain elemental profiles. The pattern of the power spectrum analysis of the Al-profile
revealed that there are significant cycles of 113.9, 87.8, 51.5, 42.2 and 25.8 μm. These cycles correspond to the Milankovitch
cycles of 53.1, 41, 24, 19.7 and 12 ka, respectively, and yield the growth rate of about 2.14 mm/Ma and an age of about 1.40
Ma for the boundary between the sub-layer 1 and sub-layer 2. We also used a drilling machine with a numerically controlled
drive to obtain high-resolution samples at 0.1mm intervals, and used the 230Thex/232Th method to date the samples. For the uppermost 1.3 mm, the growth rate was about 2.15 mm/Ma, and the age for the layer at
the depth of 3 mm was about 1.40 Ma, which coincides perfectly with the results obtained from orbital pacing. Thus, it is
considered that orbital pacing is a new and effective method to determine the growth rate of the seamount Co-rich crust. This
method is applicable for establishing a high-resolution age frame for the crusts of the world’s oceans.
Supported by China Ocean Mineral Resources R & P Association (Grant No. DY105-01-01-08) and National Natural Science Foundation
of China (Grant Nos. 40106005, 40476050) 相似文献
609.
HAN XiQiu QIU ZhongYan MA WeiLin & QIAN JiangChu Key Laboratory of Submarine Geosciences State Oceanic Administration Hangzhou China Second Institute of Oceanography 《中国科学D辑(英文版)》2009,(4)
Due to their slow growth rates, seamount Co-rich crusts are very difficult to date with high resolution and precision. This paper is to test the use of orbital pacing on the growth profile of crusts to determine high-resolution age and growth rate. Crust CB14 from the central Pacific Ocean was selected for this study. We first examined the growth pattern in detail under a reflected-light microscope and ascertained that the growth environment was stable for the sub-layer 1 (0-3 mm). We then used electron mic... 相似文献
610.
Modeling the impact of wind and waves on suspended particulate matter fluxes in the East Frisian Wadden Sea (southern North Sea) 总被引:3,自引:1,他引:2
Suspended particulate matter (SPM) fluxes and dynamics are investigated in the East Frisian Wadden Sea using a coupled modeling
system based on a hydrodynamical model [the General Estuarine Transport Model (GETM)], a third-generation wave model [Simulating
Waves Nearshore (SWAN)], and a SPM module attached to GETM. Sedimentological observations document that, over longer time
periods, finer sediment fractions disappear from the Wadden Sea Region. In order to understand this phenomenon, a series of
numerical scenarios were formulated to discriminate possible influences such as tidal currents, wind-enhanced currents, and
wind-generated surface waves. Starting with a simple tidal forcing, the considered scenarios are designed to increase the
realism step by step to include moderate and strong winds and waves and, finally, to encompass the full effects of one of
the strongest storm surges affecting the region in the last hundred years (Storm Britta in November 2006). The results presented here indicate that moderate weather conditions with wind speeds up to 7.5 m/s and
small waves lead to a net import of SPM into the East Frisian Wadden Sea. Waves play only a negligible role during these conditions.
However, for stronger wind conditions with speeds above 13 m/s, wind-generated surface waves have a significant impact on
SPM dynamics. Under storm conditions, the numerical results demonstrate that sediments are eroded in front of the barrier
islands by enhanced wave action and are transported into the back-barrier basins by the currents. Furthermore, sediment erosion
due to waves is significantly enhanced on the tidal flats. Finally, fine sediments are flushed out of the tidal basins due
to the combined effect of strong erosion by wind-generated waves and a longer residence time in the water column because of
their smaller settling velocities compared to coarser sediments.
相似文献
Karsten A. LettmannEmail: |