共查询到19条相似文献，搜索用时 125 毫秒
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本文针对地球物理中地震剖面图象的分割,进行特征提取和计算的探讨．分析了纹理结构的自相似性特性,应用分形原理进行分形维数的估测,探索了用分形特征进行图象分割的可行性． 相似文献
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中国湖泊分形特征初探 总被引：10，自引：1，他引：9
本文分形概念入手,介绍自然界（水系,云,雪,树木）普遍存在分形特征,继而用偏差法求解中国湖泊分布的分形特征,并对其进行地理意义的解释,为湖泊信息分类和湖泊数据库建设服务。 相似文献
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为研究ldquo;2005.0中国地磁测量rdquo;地磁测点空间分布均匀性特征,基于分形理论,介绍了用分形学描述地磁三分量测点空间分布均匀性的方法．该方法将测点存在的区域以不同尺度划分为相等面积的小方块,提取不同方块区域内的三分量测点的数目与尺度,在双对数坐标中进行线性拟合,直线斜率的绝对值即为分形维数Df,并以此作为评价地磁三分量测点空间分散均匀性的指标．通过对ldquo;2005.0中国地磁测量rdquo;地磁测点均匀性的定量研究,结果表明,中国大陆区域、大陆105deg;E以东和105deg;E以西区域地磁三分量测点的分形维数Df各不相同,分别为1.748, 1.796和1.609; 105deg;E以东区域比105deg;E以西区域的分形维数更接近于其嵌入维数E=2（地球表面）,意味着105deg;E以东区域的地磁三分量测点空间分布更均匀． 相似文献
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分形维数计算结果的可靠性 总被引：1，自引：1，他引：1
本文以大量分形维数计算结果的实例为基础，着重讨论了影响分维值可靠性的因素，特别指出对于未知动力学系统的自然界中的分形，很难获得真正的分形维数，若研究统计分形维数的变化特征，在采取了某些措施之后，其分维值可比，可用。 相似文献
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本文利用红外热成像手段,对微小煤样内的甲烷吸附区进行了观察,并评估其吸附特征与在煤中的分布规律.研究表明煤中存在不同尺度与甲烷吸附能力的甲烷富集区,吸附/解吸甲烷时,甲烷富集区比邻近区域具有更明显的升温/降温现象.通过图像处理的方法对不同吸附压力条件下的红外热像图中的甲烷富集区进行提取,采用盒维数进行统计发现甲烷富集区符合分形规律.试验表明随着吸附压力升高,甲烷富集区的分形维数增大,分布初值减小.对两个不同煤田的煤层气富集区进行统计表明：从微米级到千米级尺度范围内,甲烷富集区分布具有分形特征,且分形维数均在1.5~2.00之间. 相似文献
8.
从分形几何的新视角出发,分析近断层地震动的不规则性和复杂性.利用盒维数法计算了来自台湾集集地震和美国北岭地震的30条近断层地震动加速度时程的分形维数.计算结果表明,这些地震动加速度时程具有统计分形特征.近断层地震动运动特征对其分维数影响明显,滑冲效应脉冲地震动的分维数平均值最小,向前方向性效应脉冲地震动的分维数平均值居中,无脉冲地震动的分维数平均值最大,其波形不规则程度也最高.而且,地震动时程的分维数反映了其频谱特性,可作为频谱周期的表征参数.地震动的分维数D与特征周期Tc具有较强的负相关关系.最后,对于近断层地震动作用下单自由度(SDOF)体系的弹性和非弹性动力反应时程,应用盒维数法计算了其分形维数,考察了其分形性质. 相似文献
9.
应用分形及混沌理论,对油气水三相流模拟装置中采集的油气水三相泡状流混合密度波动信号进行了表征,提取的分形维数及混沌吸引子相关维分别在1.1-1.282及4.13-5.87之间.对分相含率(含水率、含气率、含油率)相同而总流速不同的情况,其分形维数及混沌吸引子相关维随总流速呈现相同的变化趋势,从功率谱特征曲线的波动程度上也验证了分形维数及混沌吸引子相关维随总流速变化趋势的正确性.另外,还对混合密度时间序列波动信号提取了最大Lyapunov指数,证明了垂直上升管中油气水三相泡状流是-混沌系统. 相似文献
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Lake-level changes are important environmental events. The paleoshorelines of a lake reflect past water levels and record information on paleoclimatic changes. Dating these events places the climatic changes in a time sequence. From shorelines ∼1, ∼4, and ∼6 m above current lake level on the eastern shore of Linggo Co, central Tibet, we collected eight samples for optically stimulated Luminescence dating. Two stratigraphic units, distinguished on the basis of color and sedimentology, were recognized beneath each shoreline. The ages obtained were 0.9 ka (upper layer) and 3.1 ka (lower layer) for lowest shoreline, 1.9 ka (upper layer), and 6.1–9.0 ka (bottom layer) for middle shoreline, and 9.6 ka for high shoreline. Two dates were considered to be unreliable due to incomplete bleaching. We attribute the higher lake levels to increased precipitation brought by the Indian monsoon in the Holocene. 相似文献
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Dorothy Sack 《地球表面变化过程与地形》1995,20(4):363-377
This paper evaluates the utility of the shoreline preservation index (s.p.i.) for estimating the age of late Pleistocene palaeolake shorelines, the relative influence of various factors on shoreline preservation, and whether shoreline preservation varies significantly with shoreline aspect. Sampled shorelines from the 3300 km2 study area, which includes the Skull, Tule and Puddle Valley portions of the Lake Bonneville basin, range in age from approximately 26 to 12 ka. Their total s.p.i. values range from 23 to 69 per cent, average 46 per cent, and do not vary significantly with shoreline aspect. The data from Skull and Tule Valleys, where studied shorelines are of known age, are analysed first in order to determine if there are statistically significant associations between variables representing shoreline preservation, age, degree of geomorphic development and duration of subaerial exposure. Pairwise correlation is then repeated using observations from all three valleys in order to determine how data from the Puddle Valley shorelines, whose hypothesized ages are not supported by radiocarbon analyses, affect the results. Results show that s.p.i. is useful as a relative-age dating tool, that the postulated ages of the Puddle Valley shorelines are ordinally correct, and that geomorphic development is not an important influence on the preservation of these late Pleistocene shorelines. The relative importance of shoreline age and the relative unimportance of duration of subaerial exposure with respect to shoreline preservation suggest that subaqueous processes play a more substantial role in shoreline obliteration than is generally suggested. 相似文献
13.
Keith Walters John J. Hutchens Jr. Eric T. Koepfler James O. Luken 《Aquatic Sciences - Research Across Boundaries》2010,72(3):309-324
Anthropogenic alteration of terrestrial shorelines can have pronounced effects on marine environments at the upland-marsh
boundary. Possible terrestrial development effects on several physical and biological variables of high-marsh habitats were
examined along developed and undeveloped shorelines in an ocean-dominated, southeastern US estuary. Analyses of sediment characteristics
suggested development of the upland boundary affected physical conditions within the high-marsh. For example, pore water salinities
were greater along undeveloped shorelines during a non-drought period even after rain events. Significant floral and faunal
differences also existed between shoreline treatments. Black needle rush stems were significantly taller and marsh periwinkle
densities significantly greater, but eastern coffee bean snail densities were significantly reduced along developed shorelines.
Benthic infaunal community abundance and composition also were significantly different between shoreline treatments with sand
fly larvae, human pest precursors, either only present or present in greater densities along developed shorelines. Sediment
respirometry experiments indicated significant differences in heterotrophic and autotrophic processes occurring between shoreline
treatments. Greater sediment surface temperatures along developed shorelines provided one possible mechanism driving high-marsh
responses to boundary alteration. The history and extent of shoreline development along with a tendency in ocean-dominated
southeastern marshes to resist change likely influenced current ecological conditions within our high-marsh study areas. A
greater understanding of the driving mechanisms producing localized effects on salt marshes and recognizing regional differences
in marsh resistance to change will facilitate predictions of shoreline development consequences and help in proposing effective
management strategies for coastal boundaries. 相似文献
14.
The Shoreline Cleanup Assessment Team (SCAT) process is a tool to assess oiled shorelines and is now an integral component of spill response operations. The key element of a SCAT survey is a systematic documentation using standard terms and definitions of the shoreline in the areas affected by an oil spill. SCAT programs were initially established to provide objective and accurate shoreline oiling information directly to cleanup operations. The role of the SCAT program has since expanded and the information generated by the field teams is used now by planners and decision-makers and to develop shoreline treatment recommendations, to select appropriate treatment techniques, and to establish the level or degree of treatment that is appropriate. This latter point is an integral part of establishing shoreline treatment criteria or standards and treatment end points. 相似文献
15.
A major thread of theoretical research on the response of shorelines to changing boundary conditions has adapted the moving-boundary approach from heat transfer and solidification/melting. On sufficiently short time scales, shorelines respond to changes in relative sea level in a simple, geometrically predictable way. On longer time scales, their behaviour becomes far more complex and interesting, because the surface over which the shoreline moves is itself continually modified by morphodynamics that depend sensitively on shoreline location. This makes the shoreline the archetype of moving-boundary problems in morphodynamics, and subject to potentially counterintuitive behaviours over time scales on which the sediment surface modifies itself as relative sea level changes. We review existing moving-boundary theories and propose two significant extensions to allow inclusion of first-order effects of waves and tides. First, we show how wave effects can be included via planform diffusion linked to river-mouth location, which results in shoreline smoothing during delta-lobe growth and localized transgression after channel abandonment. Tides produce a low-gradient region in which the sea and land overlap; we show how this can be treated in a moving-boundary framework by replacing the shoreline with a ‘mushy region' so that the handoff from land to water occurs over a zone rather than a line. We also propose that the moving-boundary approach can be readily generalized to other dynamic moving boundaries, such as those separating different regimes of river transport. The shoreline thus serves as a prototype for modelling dynamic facies boundaries along the whole source–sink system. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
16.
Many lakes in the Tibetan Plateau (TP) experienced dramatic lake level changes in the late Quaternary, as suggested by well-preserved paleo-shorelines up to ∼200 m above present lake levels. These relic shorelines provide direct geomorphic record to reconstruct past lake level fluctuation history and water volume changes, linked closely to variations in paleo-climatic controls including Asian monsoon, westerlies and glacial meltwater. In this study, 27 near-shore sediment samples from three of eight paleo-shorelines at north of Nam Co were dated by Optically Stimulated Luminescence (OSL) technique, using coarse grains of quartz and potassium feldspar.Our results indicate that: 1) S1 is the highest/most developed shoreline (+26 m). Sediment from upper part of S1 has a consistent age of ∼25 ka (nine samples from 3 gullies), suggesting a high lake level of Nam Co occurred around 25 ka. An overflow point west of Nam Co has a close elevation to that of S1 and thus limits the presence of higher lake levels; 2) sediment profile from the slightly lower S2 (+22 m) contains two parts, silty sand (6.9–8.9 ka) at the bottom and shoreline deposits atop (∼2.3 ka), suggesting Nam Co maintained a relative high lake level in the early Holocene and such lake level occurred again at about 3.0–2.0 ka; 3) In contrast to the swift variations of monsoon precipitation and glacial meltwater in the late Quaternary, water level of Nam Co remained relatively stable during the period from ∼25 ka to about early Holocene (from +26 m to +22 m), implying a continuous outflowing stage and lake infill constantly exceeds evaporation; 4) S5 (+11 m) has an age of 0.7–1.4 ka. Nam Co showed a much accelerated pace of shrinkage since about 2.0 ka in the late Holocene in roughly two steps: it dropped from +22 m to +11 m from ∼2.0 ka to 1.4 ka, and subsequently dropped another 11 m after 0.7 ka. 相似文献
17.
R. M. Briant J. Jotheri I. Al-Ameri A. Ahmed M. D. Bateman S. Engels E. Garzanti A. Nymark T. E. Reynolds 《地球表面变化过程与地形》2024,49(4):1451-1467
The water resource provided by lake basins in the western desert of Iraq is important for human occupation of areas outside the Tigris-Euphrates floodplain, both in the past and into the future. This paper presents the first geomorphological and geochronological study of the date of formation of the Najaf Sea and the only such study of any lake basin to the west of Mesopotamia. Geomorphological shoreline features and a palaeochannel linking to the Euphrates were studied and dated using optically stimulated luminescence (OSL) and radiocarbon dating. Provenance was determined using heavy mineral analysis. Past environments in the Najaf Sea were reconstructed by molluscan analysis. The earliest OSL ages date from c. 30 000 and 22 000 years ago and seem to predate lake formation. Younger OSL ages date the highest lake level at c. 19 m asl to between 1620–1760 AD (base) to 1906–1974 AD (near surface). The radiocarbon ages are affected by a freshwater reservoir effect, but the maximum ages recorded for either of the c. 15 m and c. 17 m asl shorelines are c. 800 cal. BC. This predates the first archaeological sites in the Najaf basin and is similar to maximum ages of c. 850 and c. 1100 cal. BC from the associated palaeochannel. This timing does not seem to be linked to a humid climate event. We therefore conclude that the establishment of the Najaf Sea in the Najaf basin occurred as a result of an avulsion event within the Euphrates system that diverted flow to the basin. The trigger for this avulsion event likely related to rapid sediment accumulation and may have been either autogenic or driven by human activity. This study therefore suggests that Najaf Sea formation facilitated human expansion beyond the Tigris- Euphrates floodplain and occurred due to avulsion of the Euphrates. 相似文献
18.
Pressure‐driven,shoreline currents in a perennially ice‐covered,pro‐glacial lake in Antarctica,identified from a LiCl tracer injected into a pro‐glacial stream 
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下载免费PDF全文 The distribution of streamwater within ice‐covered lakes influences sub‐ice currents, biological activity and shoreline morphology. Perennially ice‐covered lakes in the McMurdo Dry Valleys, Antarctica, provide an excellent natural laboratory to study hydrologic–limnologic interactions under ice cover. For a 2 h period on 17 December 2012, we injected a lithium chloride tracer into Andersen Creek, a pro‐glacial stream flowing into Lake Hoare. Over 4 h, we collected 182 water samples from five stream sites and 15 ice boreholes. Geochemical data showed that interflow travelled West of the stream mouth along the shoreline and did not flow towards the lake interior. The chemistry of water from Andersen Creek was similar to the chemistry of water below shoreline ice. Additional evidence for Westward flow included the morphology of channels on the ice surface, the orientation of ripple marks in lake sediments at the stream mouth and equivalent temperatures between Andersen Creek and water below shoreline ice. Streamwater deflected to the right of the mouth of the stream, in the opposite direction predicted by the Coriolis force. Deflection of interflow was probably caused by the diurnal addition of glacial runoff and stream discharge to the Eastern edge of the lake, which created a strong pressure gradient sloping to the West. This flow directed stream momentum away from the lake interior, minimizing the impact of stream momentum on sub‐ice currents. It also transported dissolved nutrients and suspended sediments to the shoreline region instead of the lake interior, potentially affecting biological productivity and bedform development. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
19.
Future shoreline changes on a sandy beach with a structure such as a jetty or groin can be estimated when wave time series is known (i.e. sequence of wave height, period, and direction). This paper presents an extension of an existing solution (Pelnard-Considere, 1956) for the linearized partial differential equation for shoreline change at an infinite jetty where waves are time varying and when the angle of the shoreline is small with respect to the waves breaking at the shoreline. The novel solution provided in this paper allows the previous constant wave condition solution to be extended to the case where wave properties (i.e. wave direction, wave height, and wave period) are time varying. Example usage of the method presented shows that shorelines may be of different final plan form shape for time varying wave conditions even though the sediment transport along adjacent beaches is not spatially varying (i.e. spatially constant) from time step to time step. Although this difference in shape may have been known previously using numerical models, it could not be proved analytically. Reversals of wave height, period, and direction time series are shown to provide different final shoreline shapes even though the time series consists of the same waves although in different ordered time. The solution provided will allow one line numerical shoreline models to be tested using an analytic solution. 相似文献