Geospatial analysis of a coastal sand dune field evolution: Jockey's Ridge, North Carolina     

Helena Mitasova  Margery Overton  Russell S. Harmon 《Geomorphology》2005,72(1-4):204-221

Preservation and effective management of highly dynamic coastal features located in areas under development pressures requires in-depth understanding of their evolution. Modern geospatial technologies such as lidar, real time kinematic GPS, and three-dimensional GIS provide tools for efficient acquisition of high resolution data, geospatial analysis, feature extraction, and quantification of change. These techniques were applied to the Jockey's Ridge, North Carolina, the largest active dune field on the east coast of the United States, with the goal to quantify its deflation and rapid horizontal migration. Digitized contours, photogrammetric, lidar and GPS point data were used to compute a multitemporal elevation model of the dune field capturing its evolution for the period of 1974– 2004. In addition, peak elevation data were available for 1915 and 1953. Analysis revealed possible rapid growth of the dune complex between 1915–1953, followed by a slower rate of deflation that continues today. The main dune peak grew from 20.1 m in 1915 to 41.8 m in 1953 and has since eroded to 21.9 m in 2004. Two of the smaller peaks within the dune complex have recently gained elevation, approaching the current height of the main dune. Steady annual rate of main peak elevation loss since 1953 suggests that increase in the number of visitors after the park was established in 1974 had little effect on the rate of dune deflation. Horizontal dune migration of 3–6 m/yr in southerly direction has carried the sand out of the park boundaries and threatened several houses. As a result, the south dune section was removed and the sand was placed at the northern end of the park to serve as a potential source. Sand fencing has been an effective management strategy for both slowing the dune migration and forcing growth in dune elevation. Understanding the causes of the current movements can point to potential solutions and suggest new perspectives on management of the dune as a tourist attraction and as a recreation site, while preserving its unique geomorphic character and dynamic behavior.  相似文献   

Ageing,migration and familial support in rural China     

《Geoforum》2014

Accelerated by economic reforms, a large scale migration of younger workers from rural to urban China has taken place since the 1990s. This has separated many adult children from their ageing parents and imposed significant challenges on traditional patterns of familial support for rural older people. These challenges are augmented by the fact that in rural China the elderly have been deprived a state pension and other welfare provisions available to urban residents.Drawing upon qualitative data from a project on ageing in rural China, this article examines the agency of older people and their families in responding to geographical separation resulting from the migration of the economically active to the cities. Through 32 life history interviews with multiple generations of nine households in one rural village, this article sheds light on the resilience and flexibility of rural households which have experienced migration and highlights the webs of interdependence that feature in the daily strategies of householding. It shows how members of the household across different geographical locations worked together to build and maintain the collective welfare of the family. In particular, this article argues that it would be over simplistic to suggest that migration is always detrimental to the older generation who stay behind. Contrary to assumptions in some migration studies and ageing literature in China, it shows that it is the breakdown of the webs of interdependence and reciprocity rather than the event of migration that will have inevitable negative effects upon old age care for the seniors in the household. Further, while highlighting the significance of householding, this article reveals the internal dynamics within a household. It identifies the role of gender in daily householding and suggests that the caring, supportive and kin-keeping roles performed mainly by women played a critical role in ensuring social and physical reproduction across generations. The article finds that while daughters took over some responsibilities which were traditionally expected from their brothers and sisters-in-law in old age support, the persistence of gendered practices and traditions in rural villages allowed sons more symbolic status and material benefits.  相似文献   

Multi-scalar inequality: Structured mobility and the narrative construction of scale in translocal Cambodia     

《Geoforum》2017

Focusing on three neighbouring villages in Cambodia, this paper argues the need for a multi-scalar interpretation of the relationship between mobility and wealth. It analyses migrant livelihoods in both sender and receiving areas to show that single scale measurements of mobility are inappropriate in the context of translocal livelihoods because livelihoods enacted across multiple places may possess multiple values of scale and mobility, each co-existing within the same migrant lifeworld. In seeking an improved conception of these complexities, the paper has combined spatial and qualitative analysis of translocal livelihoods to highlight the linkages between mobility in multiple places. On this basis, it posits that the mobility of translocal livelihoods must be assessed at least three scales: the scale appropriate to the sending environment, the scale appropriate to the receiving environment, and the scale on which potential migrations are judged. Making use of this framework allows clear relationships to be observed between mobility and inequality in both the narratives and structures of the communities under investigation.  相似文献   

探地雷达图像的正演合成与偏移处理   总被引：8，自引：2，他引：8  

邓世坤  王惠濂 《地球物理学报》1993,36(4):528-536

本文讨论了射线追踪法实现二维地电断面的探地雷达图像的正演合成问题,其中包括二维地电断面的数字拟合、多层连续界面介质中高频电磁波的反射与透射统一的运动学边界方程;根据Huygen's-Fresnel原理导出了均匀介质中二维管状体模型的衍射雷达波的计算公式;给出了用射线追踪法合成的二维地电模型的探地雷达图像;用衍射波公式合成了二维管状模型的雷达图像,并与物理模拟作了比较.在此基础上,用Kirchhoff积分法对数字模拟与物理模拟记录的雷达图像作了偏移处理,并给出了实例.  相似文献   

纵横波独立成像的弹性波逆时偏移方法   总被引：1，自引：1，他引：1  

尧德中  周熙襄 《地球物理学报》1993,(5)

本文采用逆时递推,在空间域完成纵横波分离,同时实现了位移场成像和纵、横波的独立成像。模拟数据与实际资料试算表明,对纵波和横波分别成像不仅有理论意义,而且有明显的应用价值。文中还就偏移速度对成像结果的影响和实际资料的预处理问题进行了讨论。  相似文献   

Changing poverty distribution in Bolivia: the role of rural–urban migration and urban services     

Greg O’Hare  Sara Rivas 《GeoJournal》2007,68(4):307-326

Bolivia is a country with high levels of poverty and inequality among its peoples and regions. For the nation and its urban and rural areas, trends in the social and spatial distribution of poverty (and extreme poverty) are identified from 1976 to 2003 using UBN data with minor support where appropriate from poverty lines. The main survey between 1992 and 2001 uses composite and selected UBN to track detailed poverty change for the country’s nine departments, its ten largest cities and a selection of other smaller urban and rural municipalities. Because of rising background increases in population in the various surveyed administrative units, many instances of relative reductions in poverty are accompanied by rising absolute increases. Marked spatial variations in poverty and development in the country over the last several decades are identified as the main driver for the country’s quickening pace of rural–urban migration. As a result, the paper concludes by assessing two different but closely related views. One investigation tests the notion that because more poor people have been living in Bolivia’s cities than in its rural areas since the mid to late 1990s, rapid rural–urban migration has simply shifted the locus of poverty from the countryside to the cities in a process called, the ‘urbanisation of poverty.’ A second, more challenging, investigation assesses the view that the flow of poor rural people to the better serviced urban areas of Bolivia has actually acted to alleviate national poverty levels.  相似文献   

大地电磁偏移成像技术的研究进展及其解决复杂地质问题的能力   总被引：1，自引：0，他引：1       下载免费PDF全文

于鹏  王家林  吴健生  陈冰 《地震地质》2001,23(2):238

总结和分析了大地电磁场成像技术的研究现状 ,在Zhdanov等对偏移电磁场的研究和成像技术基础上 ,提出了改进的有限差分法大地电磁场偏移成像技术 ,使差分方程精度和成像分辨率有了明显的提高 ,将前人大地电磁场偏移成像的模型试验研究推进到适用于复杂地电模型和实际资料处理解释的阶段 ,并通过松辽盆地大地电磁测深资料的偏移成像处理和解释展示了该方法的有效性和实用性  相似文献   

澜沧-耿马等强震迁移活动与地电前兆场时空关系     

李晓玲  汪志亮  余素荣 《地震》1996,(3)

研究1988年11月至1990年10月近2a时间内,在22°～36°N,98°～104°E地区连发性的5次6级以上迁移地震与地电前兆的时空关系。结果表明,这组连发性迁移强震发生之前,地电前兆在南北两地区观测到两个应力相对集中区。随着南部系统内应力不断向北调整,发生了多次强震。这组连发性的强震孕育,包括它们各自前兆场分布和发育,彼此并不是孤立的,而是彼此呼应的。  相似文献   

陕西地区地震活动性的初步分析     

许俊奇 《内陆地震》1993,7(3):240-244

依据震中迁移、频度变化曲线、能量释放曲线、震级频度关系和时间序列的预测方法等,对陕西地区的地震活动性进行了初步分析,认为:陕西地区M_L>3.5级的地震活动存在着明显的由北向南、自东向西的迁移特点,其地震活动水平比较正常,今后5年内可能发生M_L≥4.3级地震。  相似文献   

可用于复杂地质体的波动方程基准面技术   总被引：7，自引：7，他引：0  

陈树文  刘洪 《地球物理学进展》2002,17(3):365-369,T001

提出改进的波动方程基准面方法,用于解决地表一致性问题,通过基准面的下移,可以使深部的信号增强,变多值走时为单值走时,从根本上消除了上覆层速度横向不均匀的影响,从而可以更好地解决复杂地质体成像问题。作者从原理上对上述观点给予了证明,而且给出利用波动方程基准面有限差分法做的实例－－大庆油田“陆相断隐模型”。  相似文献