Characterizing and identifying bedforms in the wandering reach of the lower Yellow River

The lower Yellow River （LYR） is a fully alluvial system with a fine-grained bed that has a high proportion of silt.Bathymetric survey data collected with a Multi-Beam Echo Sounder （MBES） from the wandering reach of the LYR indicates that the bedforms are characterized by large aspect ratios （wavelength/height）and low lee-side angles.Since the Xiaolangdi Reservoir （XLD） has been operational in the middle reach of the Yellow River,bedforms have been dominated by two-scales of dunes,that is,a frame...     

面向关系数据库扩展的自适应影像金字塔模型

随着遥感技术的发展,特别是传感器分辨率的提高,影像数据量日益增长,这对高效、智能地管理海量数据提出了更高的要求,如何有效、智能地存取海量遥感数据成为当前越来越热门的话题。本文针对空间数据管理系统的发展现状,结合数据库存储、网络传输和客户端的硬件情况,从影像数据切片和影像数据的细节层次(level of detail,LOD)模型两个层面来解决遥感数据的存储问题,提出了自适应的遥感影像切片机制,以及与之相适应的LOD模型构建方法。通过试验证实,该影像管理机制能够在多种不同的数据库、网络和客户端条件下实现影像数据智能化高效存储与访问。本文的研究为高效的影像数据管理提供了可行的思路和方法,有助于在C/S架构的网络环境下实现基于数据库技术的遥感影像数据的高效存取和管理。     

瓦片影像地图快速配准与融合方法实现

为解决天地图中海量影像瓦片的快速配准和融合问题,文章针对主节点和省市级分节点影像瓦片地图的特点,设计了基于金字塔模型的地图瓦片快速空间精确配准和影像融合算法,并利用.NET语言编程实现了该算法。通过在天地图·四川建设中的实际应用表明,该算法能解决全色(黑白)影像无法应用于天地图省市级分节点建设的难题,对天地图省市级分节点建设有一定的应用价值。但由于融合数据范围较大且不同地区的数据质量存在差异,在融合过程中仍然需要大量的人机交互工作。     

察尔汗盐湖区线形沙丘下伏湖相地层的释光年代及其环境意义

本研究尝试使用钾长石多步升温红外后红外法(MET-pIRIR)对察尔汗盐湖北侧线形沙丘下伏古湖相沉积物进行年代测定,并初步探讨其古环境意义.结果表明:钾长石MET-pIRIR250法能够得到等效剂量坪区,说明长石信号能够充分晒退并且异常衰减对测年结果的影响可以忽略,从而保证了测年结果的可靠性;古湖相沉积顶部200-18...     

Crescentic dunes at Schiermonnikoog,The Netherlands

This paper describes the appearance and maintenance of crescentic dunes in high wind speed conditions on a frozen beach at Schiermonnikoog, The Netherlands. The dunes were cresentic forms with horns. They were barchanoidal in plan view, but had reverse morphologies to typical barchans: the highest and steepest slopes were upwind and led to long low slopes downwind. Slipfaces were absent. It is hypothesized that such crescentic dunes may be a stable aerodynamic form under high to very high (c. 15–20 m s⁻¹) flow conditions. © 1997 by John Wiley & Sons, Ltd.     

Effect of non-migrating bars on dune dynamics in a lowland river

As dunes and larger-scale bed forms such as bars coexist in rivers, the question arises whether dune dynamics are influenced by interaction with the underlying bed topography. The present study aims to establish the degree to which dune characteristics in two and three dimensions are influenced by an underlying topography dominated by non-migrating bars. As a case study, a 20 km stretch in the Waal River in the Netherlands is selected, which represents a sand-bed lowland river. At this location, longitudinal training dams (LTDs) have recently been constructed to ensure sufficient navigation depth during periods with low water levels, and to reduce flood risk. By using data covering 2-year-long periods before and after LTD construction, the robustness of the results is investigated. Before LTD construction, dune characteristics show large variability both spatially and temporally, with dunes being longer, lower, less steep and having a lower lee side angle when they are located on bar tops. The correlation between dune characteristics and the underlying bed topography is disrupted by unsteady conditions for which the dunes are in a state of transition. The bar pattern causes tilting of dune crest lines, which may result from a transverse gradient in bedload sediment transport. As a result of LTD construction, the hydraulic and morphological conditions have changed significantly. Despite this, the main conclusions still hold, which strengthens the validity of the results. ©2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

古尔班通古特沙漠固定与半固定沙丘成因初探

处于干旱荒漠区的古尔班通古特沙漠因降水、冬季的积雪、悬湿砂层、丘间地和背风坡的植被、沙丘表层微弱的分化、砂物质粒度等因素的综合影响 ,以固定和半固定沙丘为主。由于沙丘的稳定性差 ,人类活动过程中应加强对它的保护。     

The Socio-Economic Costs and Benefits of Coastal Habitat Rehabilitation and Creation

This paper provides a comprehensive overview of the merits and limitations of using an economics based approach to assess and implement initiatives for coastal habitat rehabilitation and creation. A review of the literature indicates that habitat rehabilitation/creation costs vary widely between and within ecosystems. For coral reefs, costs range from US$ 10,000 to 6.5 million/hectare (ha);¹ for mangroves US$ 3000–510,000/ha; for seagrasses US$ 9000–680,000/ha and for saltmarshes US$ 2000–160,000/ha. A review of the economic benefits derived from various coastal habitats based on a ‘Total Economic Value’ approach (i.e. accounting for direct and indirect uses, and ‘non-uses’) reveals that many thousands of US$ per hectare could ultimately accrue from their rehabilitation/creation. The paper concludes that despite its limitations, the ‘benefit-cost analysis’ framework can play an important role both in assessing the justification of coastal habitat rehabilitation/creation initiatives, and by helping to improve the overall effectiveness of such initiatives.     

Dominance of an 150-Year Cycle of Sand-Supply Change in Late Holocene Dune-Building along the Eastern Shore of Lake Michigan

Outcrops of buried soils on lake-plains and glacial headlands along Lake Michigan's eastern shore suggest that periodic dune-building has occurred there after relatively long (≥100 yr) periods of low sand supply. We located, described, and radiocarbon dated 75 such buried soils that crop out in 32 coastal dune fields beside the lake. We assume that peaks in probability distributions of calibrated ¹⁴C ages obtained from wood, charcoal, and other organic matter from buried A horizons approximate the time of soil burial by dunes. Plotted against a late Holocene lake-level curve for Lake Michigan, these peaks are closely associated with many 150-yr lake highstands previously inferred from beach ridge studies. Intervening periods of lower lake levels and relative sand starvation apparently permitted forestation and soil development at the sites we studied. While late Holocene lake-level change led to development and preservation of prominent foredunes along the southern and southwestern shores of Lake Michigan, the modern dune landscape of the eastern shore is dominated by perched dunes formed during 150-yr lake highstands over the past 1500 yr.