Creating high-resolution bare-earth digital elevation models (DEMs) from stereo imagery in an area of densely vegetated deciduous forest using combinations of procedures designed for lidar point cloud filtering

For areas of the world that do not have access to lidar, fine-scale digital elevation models (DEMs) can be photogrammetrically created using globally available high-spatial resolution stereo satellite imagery. The resultant DEM is best termed a digital surface model (DSM) because it includes heights of surface features. In densely vegetated conditions, this inclusion can limit its usefulness in applications requiring a bare-earth DEM. This study explores the use of techniques designed for filtering lidar point clouds to mitigate the elevation artifacts caused by above ground features, within the context of a case study of Prince William Forest Park, Virginia, USA. The influences of land cover and leaf-on vs. leaf-off conditions are investigated, and the accuracy of the raw photogrammetric DSM extracted from leaf-on imagery was between that of a lidar bare-earth DEM and the Shuttle Radar Topography Mission DEM. Although the filtered leaf-on photogrammetric DEM retains some artifacts of the vegetation canopy and may not be useful for some applications, filtering procedures significantly improved the accuracy of the modeled terrain. The accuracy of the DSM extracted in leaf-off conditions was comparable in most areas to the lidar bare-earth DEM and filtering procedures resulted in accuracy comparable of that to the lidar DEM.     

南极洲赖特谷万达盐湖中铬的垂直迁移

南极洲万达湖湖水上部为氧化环境,铬浓度较低,Cr~(6+)占主导地位,主要以CrO_4~(2-)形式存在;下部为还原环境,铬浓度高,Cr~(3+)为主,以Cr(OH)_2~+和Cr(OH)~(2+)形式存在。湖水中锰、铁的氧化物及氢氧化物颗粒对铬离子的吸附和释放过程,控制了湖水铬浓度的变化。     

Climate change and coastal megacities: Adapting through mobility

Climate change poses threats to individuals, communities, and cities globally. Global conversations and scholarly debates have explored ways people adapt to the impacts of climate change including through migration and relocation. This study uses Lagos, Nigeria as a case study to examine the relationship between flooding events, migration intentions as a preferred adaptation, and the destination choices for affected residents. The study draws on a mixed-methods approach which involved a survey of 352 residents and semi-structured interviews with 21 residents. We use a capability approach to analyze mobility decisions following major or repetitive flood events. We found that the majority of affected residents are willing to migrate but the ability to do so is constrained by economic, social, and political factors leading to involuntary immobility. Furthermore, intra-city relocation is preferred to migration to other states in Nigeria or internationally. These findings challenge popular Global South-North migration narratives. Indeed, some residents welcome government-supported relocation plans but others remain skeptical due to lack of trust. Community-based relocation may therefore be preferred by some Lagosians. Overall, this study contributes a nuanced understanding of mobility intentions in response to climate-induced flooding in one of the world’s largest coastal cities.     

1800年以来长江中下游地震区中强地震集丛分布和迁移特征

本文对长江中下游地震区1800年以来中强地震活动进行了分区讨论,总结其活动规律,类比外推对该区M≥5.5级地震活动趋势作了估计。     

标量波动方程全倾角有限差分偏移

传统的有限差分法偏移是建立在单程波波动方程的不同阶数的近似式基础上的。因此,各阶近似式的偏移方法都存在一个倾角极限问题。克服倾角极限和提高极限倾角是八十年代以来有限差分偏移技术的研究目标。在这方面取得了显著的进展。本文从标量波动方程出发,通过函数替代,将它化为一个等价的方程组,用有限差分法解此方程组进行波场外推,实现全倾角偏移成象的目的。与国外已有的使用波动方程全式进行偏移的方法相比较,除方法原理本身不同外,该方法具有稳定性好,计算工作量较少的优点。     

油气成藏系统──概念、分类和应用

介绍了油气成藏系统的有关概念、成因分类及其在勘探中的应用。油气成藏系统将油气藏形成的各种地质因素、过程及其历史作为一个有机联系的系统进行整体研究。成熟烃源岩的质量、数量和油气显示情况是油气成藏系统分析中的两个重要方面。在一个油气成藏系统中，三个关键因素是源岩充注能力、烃类运移方式和捕集方式，它们构成油气成藏系统成因分类的依据。油气成藏系统理论是油气远景评价工作十分有效的工具，已成功地应用于生产实践中。油气成藏系统理论已成为近年来石油地质学领域的热点之一。     

Successful British Migration to Australia—what lies beneath the macro-level?

ABSTRACT

What is successful migration? At a macro-socio-political level migration by individuals may appear to be successful when it has met the objectives of governments, industries and domestic profit makers. However, delving beneath the surface can reveal contradictions and other measures of success at the individual, or micro-level. Within a broader critical historical ethnography, we interviewed 26 post-World War 2 (WW2) British migrants living in South Australia. All interviewees could be viewed as successful at the macro-level, having remained in Australia for many years and having established multi-generational Australian families. Their migration was a ‘success’ when measured against the priorities that were actively promoted by Australian governments in the post-WW2 period. At a micro-level, the migrants involved in this study reported mixed outcomes. While migration did result in self-identified aims of migration including employment, opportunities and adventure, some migrants reported high levels of distress and longing, linked to loss and dislocation from people and places in geographically distant locales. For some, these feelings extended into the present, raising questions over the ‘success’ of their migration experiences at a personal level. We argue that pro-active migration recruitment—such as that undertaken by Australian governments in the post-WW2 period—has the potential to pressure some persons into migration, creating ongoing and unresolvable tensions. Experiences of such disruptions merit further exploration to develop deeper critical understandings of migration success.     

Temporal changes of fault seal and early charge of the Maui Gas-condensate field,Taranaki Basin,New Zealand

Fault seal due to juxtaposition or the generation of low-permeability fault rock has the potential to change through time with displacement accumulation. Temporal variations in cross-fault flow of hydrocarbons have been assessed for the Cape Egmont Fault (CEF), Taranaki Basin New Zealand, using displacement backstripping, juxtaposition and Shale Gouge Ratio (SGR) analysis. The timing of hydrocarbon migration and charge of the giant Maui Gas-condensate Field across the CEF have been assessed using seismic reflection lines (2D & 3D), coherency cubes, VShale curves from the Maui-2 well and PetroMod modelling. Displacement–backstripping analysis suggests that between the Late Miocene and early Pleistocene (5.5 and 2.1 Ma) sandstone reservoir units of the Maui Field (Mangahewa, Kaimiro and Farewell Formations) and underlying source rocks (Rakopi Formation) were partly juxtaposed across the CEF with low SGRs (< 0.2) present in the fault zone. Following 2.1 Ma SGRs increased to 0.2–0.55 adjacent to the Eocene–Palaeocene reservoir succession which was not in juxtaposed contact with source rocks. PetroMod modelling using these SGR values and juxtaposition relationships supports cross-fault flow prior to 2.1 Ma with later charge across the fault being less likely. Gas chimneys and the gas–water contact in the Eocene reservoir proximal to the fault suggest that despite limited cross-fault flow, upward leakage of hydrocarbons from the reservoir occurred after 2.1 Ma, possibly associated with active fault movement or fracturing related to faulting, and may account for the loss of an early oil phase.     

Agriculture,irrigation and drought induced international migration: Evidence from Mexico

There is now substantial empirical evidence that climatic variability increases international migration, but relatively little is known about the mechanism driving the association and about adaptations that may reduce it. We use detailed data on migrants from Mexico to the U.S. to provide evidence in support of the hypothesis that drought induced migration from Mexico to the U.S. is mediated by agricultural income shocks. Migration rates increase in drought years, but only in Mexico’s drier regions, and the response is stronger in states and seasons in which agricultural production is also more sensitive to precipitation. Moreover, among the sample, only farmers display a significant increase in migration rates in drought years, and the effect is substantially weaker for households with access to irrigation.