Detection of gullies in roughly textured terrain using airborne laser scanning data     

Amit Baruch  Sagi Filin 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(5):564-578

Airborne laser scanning data contain information about surface features, some of which are of subtle form. These features are usually embedded within the terrain, and rarely form distinct shape-transition to their surroundings. While some efforts have been made in extracting linear elements from laser scanning data, attention was mostly turned to dominant elements that are very clear and distinct. We present in this paper a detection model for gullies of various dimensions using airborne laser scanning data. Gullies are regarded as one of the main landform-reshaping agents, having a pejorative effect on the environment and on regional development. They are commonly observed along receding lakes as a common response to water-level drop. The paper demonstrates how a multi-scale approach enables the extraction of various gully forms, from well developed to subtle. It then proposes an optimization driven model for handling fragmentation in the detection. Results show that using the proposed model, gully networks can be reconstructed and ∼30 cm deep features can be identified and separated from their surroundings using moderate point density data.  相似文献   

Research Progress on Morphodynamics of Coastal Sandy Blowout     

Shaoyun Zhang  Yuxiang Dong 《地球科学进展》2019,34(10):1028-1037

As a type of negative topography in sand land, blowout has always been one of the main research object of aeolian geomorphology. Especially, multi-directions and long-term research has been conducted internationally on basic morphology, development process and dynamic mechanism of coastal sandy blowout. Based on the systematic review of research on coastal sandy blowout, the main progress of research on coastal sandy blowout in morphological evolution, morpho-dynamic process, and research methods was summarized. In consideration of the disadvantages of research on coastal sandy blowout, it was proposed that, at present, the research on coastal sandy blowout in China should strengthen the further research on the evolution mechanism, morphology-material-dynamic process and numerical simulation of different types of blowouts, and attach importance to the influence of blowout on the beach-dune dynamic environment and foredune restoration.  相似文献   

电离层F₁-F₂谷区结构及其变化          下载免费PDF全文

苏元智  黄倍榆 《地球物理学报》1991,34(2):139-146

本文给出一个从电离层频高图提取F₁-F₂谷区信息的剖面分析方法.利用该方法分析处理了武昌站的垂测记录,揭示了我国中低纬地区上空F₁-F₂谷区形态的某些变化规律和地区特色.对该类谷区的形成机制进行了初步探讨,认为在光化理论中若考虑基态与亚稳态两种氧离子的不同作用,可以说明该谷区的出现和基本变化趋势.  相似文献   

First-order drainage basin morphology—definition and distribution     

Alan Marcus 《地球表面变化过程与地形》1980,5(4):389-398

First-order drainage basin morphology consists of two complementary regions: a headwater region, the valley head; and a stream region, the channelway (Figure 1). Each subbasin's morphology is represented by a set of principal components factors that include the properties of area, length, slope, relief, elongation, and plan curvature. The channelway region is a highly-integrated morphological unit that is dominated by a size-shape factor, indicative of an organized flow system and the presence of a permanent channel. The valley head region shows little integration of its morphological factor set, and this is reflected by its lack of a permanent channel. The valley head-channelway definition is utilized to classify first-order basins into three morphological groups or types. Basin type is related to basin location within the larger drainage network, and this relation helps to explain variations in subbasin morphology. The channelway's morphologic properties are influenced by the location of the first-order basin's bifurcation or junction within the higher-ordered network; and valley head morphology is related to the location of the basin's divide position within the drainage net.  相似文献   

CHANGES IN CHANNEL PATTERN OF RIVER GANGA BETWEEN MUSTAFABAD AND RAJMAHAL, GANGETIC PLAINS SINCE 18TH CENTURY   总被引：1，自引：0，他引：1  

Prabhata K. SWAMEE  Barham PARKASH  Jayaprakash V THOMAS  Satvindar SINGH 《国际泥沙研究》2003,18(3)

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Refuge selection by two sympatric species of arid-dwelling land snails: Different adaptive strategies to achieve the same objective     

G. Moreno-Rueda   《Journal of Arid Environments》2007,68(4):588-598

Terrestrial gastropods, especially those dwelling in dry habitats such as the Mediterranean, are highly susceptible to dehydration. In this study, the use of refuges by Iberus gualtieranus gualtieranus and Sphincterochila candidissima is compared. These two species belong to families with different distribution ranges, but they live in sympatry on a mountain in southern Spain with a dry Mediterranean climate. I. g. gualtieranus used mainly rock crevices as refuges, consistently throughout the year. S. candidissima hibernated beneath humus during autumn and winter (I. g. gualtieranus did not hibernate). In spring, S. candidissima seemed active, while I. g. gualtieranus was already aestivating. In summer, S. candidissima aestivated on vegetation, while I. gualtieranus aestivated deep within crevices. These differences in the use of refuges may be explained on the basis of the need for more protection by I. g. gualtieranus because of its morphology, which is less suited to the dry habitat, but has evolved to enable this species to exploit karstic crevices as refuges more efficiently. These results illustrate that behaviour and morphology interact allowing both species to coexist in sympatry in an arid environment using different adaptive strategies.  相似文献   

Histological and morphological alterations induced by copper exposure in Laeonereis acuta (Polychaeta, Nereididae)     

L. A. Geracitano  C. Luquet  J. M. Monserrat  A. Bianchini   《Marine environmental research》2004,58(2-5):263

Laeonereis acuta (Polychaeta, Nereididae) was collected in an unpolluted (UP) and an polluted (P) site at the Patos Lagoon estuary (Southern Brazil) and maintained under control conditions (UPC and PC, respectively) or exposed to waterborne copper (UPCu and PCu; 500 μg Cu/l), for 48 h. Four groups (aaUPC, aaPC, aaUPCu, and aaPCu) were also pre-exposed for 48 h to ascorbic acid (aa; 0.1 mM) before copper exposure. Histological and morphological alterations, as well as oxygen consumption changes were evaluated. Independently of the sampling site and the pre-exposure to the ascorbic acid, morphological abnormalities were evident in more than 80% of worms exposed to copper. Conspicuous histological changes (coeloma obliteration, cuticle separation from the epidermis, and absence of dorsal vessel) were also observed. In addition, PCu worms showed loss of the digestive epithelium and coiling behavior. Similar oxygen consumption values were observed in control and copper exposed worms.  相似文献   

A statistical-dynamical method for predicting long term coastal evolution     

D. E. Reeve  C. A. Fleming 《Coastal Engineering》1997,30(3-4)

A new approach to the problem of predicting long term coastline evolution is described. The cumulative effect of shoreline processes is inferred by inverting an extended form of one-line equation. Results from the inversion process are then used to predict future coastal evolution on the basis of past historical changes. The data required are charts showing the historical changes in coastline position. By way of validation, the model is applied to a region on the east coast of the United Kingdom where a 12 year forecast is made and compared against recent aerial survey data. The results are encouraging and suggest that the method has a predictive capability, suitable for strategic studies of regional shoreline evolution.  相似文献   

Morphological and textural diversity of the Steens Basalt lava flows,Southeastern Oregon,USA: implications for emplacement style and nature of eruptive episodes     

Ninad R. Bondre  William K. Hart 《Bulletin of Volcanology》2008,70(8):999-1019

This study focuses on Middle Miocene tholeiitic flood basalt lava flows from the Oregon Plateau, northwestern USA (Steens Basalt), and is the first to comprehensively document and evaluate their morphology. Field observations of flows from several sections within and proximal to the main exposures at Steens Mountain have been supplemented with textural and geochemical data, and are used to offer preliminary insights into their emplacement. Compound pahoehoe flows of variable thickness appear to be common throughout the study area, laterally and vertically. These tend to be plagioclase phyric and the morphology and disposition of constituent flow lobes are quite similar to those from other provinces such as Hawaii and the Snake River Plain. Classic a’a flows with brecciated upper and basal crusts are not abundant, but by no means uncommon. Flows with characters different from typical pahoehoe and a’a are also common. Such flows display a range in morphology; flows with preserved upper crusts but brecciated basal crusts, as well as those displaying well-developed flow-top breccias and preserved basal crusts (rubbly pahoehoe) are observed. The Steens Basalt appears to display greater morphological and textural diversity at the outcrop scale than that described for some other flood basalt provinces. The abundant compound pahoehoe flows (often rich in plagioclase phenocrysts) were likely emplaced during slow but sustained eruptive episodes; their constituent lobes show clear evidence for endogenous growth. The relatively aphyric flows with brecciated surfaces (including a’a) hint at higher strain rates and/or higher viscosity, probably caused by higher effusion rates. A couple of sections are characterized by compositionally similar, but morphologically different flows that were possibly part of the same eruption. While differences in pre-eruptive topography could explain this, it is also possible that certain physical parameters changed substantially and abruptly during eruption and that such changes were accompanied by differentiation processes within the plumbing system. It is possible that such observations indicate temporal fluctuations within complex magmatic and eruptive systems, and deserve closer scrutiny.  相似文献   

Physical volcanology and structural development of Cerro Azul Volcano, Isabela Island, Galápagos: implications for the development of Galápagos-type shield volcanoes     

Terry Naumann  Dennis Geist 《Bulletin of Volcanology》2000,61(8):497-514

3 ) erupted from circumferential vents near the summit. These flows are nearly an order of magnitude smaller in volume than the predominantly aa flows erupted from radial eruptive fissures near the break in slope (0.06–0.1 km³). The differences in volume and flow morphology with altitude are due to slower eruption rates from summit vents than from flank vents, which, in turn, are attributable to the different heights the magmas must ascend from shallow reservoirs. These observations support the contention that the steep upper flanks were constructed by the buildup of short lava flows rather than by the structural deformation of originally gently dipping flanks. In addition to the higher eruption rates, a subdued lower flank geometry is promoted by the deposition of lava deltas onto the shallow Galápagos platform on the western, northern, and eastern flanks of the volcano. ⁴⁰Ar/³⁹Ar geochronology and volume estimates show that, despite their morphologic differences, the growth of the western Galápagos shields has been nearly synchronous, precluding an evolutionary model for their development. The wide variations in elevation, volume, area, and the distribution of slope angles among the western volcanoes can be linked instead to different long-term eruption rates and, to a lesser degree, the position of each volcano relative to the edge of the Galápagos platform. Received: 24 September 1998 / Accepted: 7 August 1999  相似文献