Using UAV acquired photography and structure from motion techniques for studying glacier landforms: application to the glacial flutes at Isfallsglaciären          下载免费PDF全文

Jeremy C. Ely  Conor Graham  Iestyn D. Barr  Brice R. Rea  Matteo Spagnolo  Jeff Evans 《地球表面变化过程与地形》2017,42(6):877-888

Glacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small‐scale fragile geomorphological features which could provide insight into subglacial or submarginal processes. Subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor‐relief landforms as wind, weather, water and vegetation impact on the newly exposed surface. Ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes. Here we used an unmanned aerial vehicle to capture close‐range aerial photography of the foreland of Isfallsglaciären, a small polythermal glacier situated in Swedish Lapland. An orthophoto and a digital elevation model with ~2 cm horizontal resolution were created from this photography using structure from motion software. These geospatial data was used to create a geomorphological map of the foreland, documenting moraines, fans, channels and flutes. The unprecedented resolution of the data enabled us to derive morphological metrics (length, width and relief) of the smallest flutes, which is not possible with other data products normally used for glacial landform metrics mapping. The map and flute metrics compare well with previous studies, highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution. The vast majority of flutes were found to have an associated stoss‐side boulder, with the remainder having a likely explanation for boulder absence (burial or erosion). Furthermore, the size of this boulder was found to strongly correlate with the width and relief of the lee‐side flute. This is consistent with the lee‐side cavity infill model of flute formation. Whether this model is applicable to all flutes, or multiple mechanisms are required, awaits further study. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Hydrological Outlook UK: an operational streamflow and groundwater level forecasting system at monthly to seasonal time scales     

Christel Prudhomme  Shaun Harrigan  David Boorman  Jeff Knight  Victoria Bell 《水文科学杂志》2017,62(16):2753-2768

This paper describes the development of the first operational seasonal hydrological forecasting service for the UK, the Hydrological Outlook UK (HOUK). Since June 2013, this service has delivered monthly forecasts of streamflow and groundwater levels, with an emphasis on forecasting hydrological conditions over the next three months, accompanied by outlooks over longer time horizons. This system is based on three complementary approaches combined to produce the outlooks: (i) national-scale modelling of streamflow and groundwater levels based on dynamic seasonal rainfall forecasts, (ii) catchment-scale modelling where streamflow and groundwater level models are driven by historical meteorological forcings (i.e. the Ensemble Streamflow Prediction, ESP, approach), and (iii) a catchment-scale statistical method based on persistence and historical analogues. This paper provides the background to the Hydrological Outlook, describes the various component methods in detail and then considers the impact and usefulness of the product. As an example of a multi-method, operational seasonal hydrological forecasting system, it is hoped that this overview provides useful information and context for other forecasting initiatives around the world.  相似文献   

A comparison of biological trends from four marine ecosystems: Synchronies, differences, and commonalities   总被引：1，自引：1，他引：0  

Jason S. Link  William T. Stockhausen  Georg Skaret  William Overholtz  Bernard A. Megrey  Harald Gjster  Sarah Gaichas  Are Dommasnes  Jannike Falk-Petersen  Joseph Kane  Franz J. Mueter  Kevin D. Friedland  Jonathan A. Hare 《Progress in Oceanography》2009,81(1-4):29

Major features of four marine ecosystems were analyzed based on a broad range of fisheries-associated datasets and a suite of oceanographic surveys. The ecosystems analyzed included the Gulf of Maine/Georges Bank in the Northwest Atlantic Ocean, the Norwegian/Barents Seas in the Northeast Atlantic Ocean, and the eastern Bering Sea and the Gulf of Alaska in the Northeast Pacific Ocean. We examined survey trends in major fish abundances, total system fish biomass, and zooplankton biomasses. We standardized each time series and examined trends and anomalies over time, using both time series and cross-correlational statistical methods. We compared dynamics of functionally analogous species from each of these four ecosystems. Major commonalities among ecosystems included a relatively stable amount of total fish biomass and the importance of large calanoid copepods, small pelagic fishes and gadids. Some of the changes in these components were synchronous across ecosystems. Major differences between ecosystems included gradients in the magnitude of total fish biomass, commercial fish biomass, and the timing of major detected events. This work demonstrates the value of comparative analysis across a wide range of marine ecosystems, suggestive of very few but none-the-less detectable common features across all northern hemisphere ocean systems.  相似文献   

Recent climate forcing and physical oceanographic changes in Northern Hemisphere regions: A review and comparison of four marine ecosystems     

K.F. Drinkwater  F. Mueter  K.D. Friedland  M. Taylor  G.L. Hunt Jr.  J. Hare  W. Melle 《Progress in Oceanography》2009,81(1-4):10

As part of a project comparing the structure and function of four marine ecosystems off Norway and the United States, this paper examines the oceanographic responses to climate forcing, with emphasis on recent changes. The four Northern Hemisphere ecosystems include two in the Pacific Ocean (Bering Sea and Gulf of Alaska) and two in the Atlantic Ocean (Georges Bank/Gulf of Maine and the Barents/Norwegian Seas). Air temperatures, wind forcing and heat fluxes over the four regions are compared as well as ocean hydrography and sea-ice conditions where seasonal sea ice is found. The long-term interannual variability in air temperatures, winds and net heat fluxes show strong similarity between adjacent ecosystems and within subregions of an ecosystem, but no significant correlations between Pacific and Atlantic ecosystems and few across the Atlantic. In spite of the lack of correlation between climate forcing and ocean conditions between most of the ecosystems, recent years have seen record or near record highs in air and sea temperatures in all ecosystems. The apparent causes of the warming differ. In the Atlantic, they appear to be due to advection, while in the Pacific temperatures are more closely linked to air-sea heat exchanges. Advection is also responsible for the observed changes in salinity in the Atlantic ecosystems (generally increasing salinity in the Barents and Norwegian Seas and decreasing in the Gulf of Maine and Georges Bank) while salinity changes in the Gulf of Alaska are largely related to increased local runoff.  相似文献   

Symplectic integrators for long-term integrations in celestial mechanics     

Brett Gladman  Martin Duncan  Jeff Candy 《Celestial Mechanics and Dynamical Astronomy》1991,52(3):221-240

We discuss the use of symplectic integration algorithms in long-term integrations in the field of celestial mechanics. The methods' advantages and disadvantages (with respect to more common integration methods) are discussed. The numerical performance of the algorithms is evaluated using the 2-body and circular restricted 3-body problems. Symplectic integration methods have the advantages of linear phase error growth in the 2-body problem (unlike most other methods), good conservation of the integrals of the motion, good performance for moderately eccentric orbits, and ease of use. Its disadvantages include a relatively large number of force evaluations and an inability to continuously vary the step size.  相似文献   

Geographical accessibility and Kentucky's heart-related hospital services   总被引：2，自引：0，他引：2  

Timothy S. Hare  Holly R. Barcus   《Applied geography (Sevenoaks, England)》2007,27(3-4):181-205

Cardiovascular diseases (CVDs) are a leading cause of mortality in the US. Rates of mortality vary spatially and demographically, influenced not only by individual patient characteristics but also by levels of accessibility to hospital services and facilities. In 2000, Kentucky ranked third in the nation for heart-related deaths. The purpose of this paper is to assess geographical accessibility and service utilization related to ambulatory care sensitive CVDs in Kentucky. This study utilizes the Kentucky Hospital Discharge Database to evaluate service utilization and the Compressed Mortality File to examine mortality related to CVDs. A spatial statistical comparison of the geographical distribution of service usage and travel time to hospitals assists in assessing the relationship between accessibility and health. Our findings suggest that the distribution of utilization and mortality is geographically variable. People living in rural areas travel further to services; populations residing more than 45 min from health facilities are more likely to be socially and economically marginalized. Spatial clustering of high rates of hospital utilization occurs in areas with lower accessibility.  相似文献   

Institutions, the governance of quality and on-farm value retention for Indonesian specialty coffee     

Jeff Neilson 《Singapore journal of tropical geography》2007,28(2):188-204

Fluctuating global commodity prices affect the livelihoods of millions of tropical farmers worldwide. In recent years, systemic oversupply of many tropical agricultural products, grown in countries such as Indonesia, has meant that agricultural incomes have continuously fallen below subsistence levels. Within an increasingly open global trade regime, along with the limited ability of governments to protect domestic farm prices, quality-informed product differentiation appears to offer an escape route from the trap of low commodity prices. However, ownership and governance of quality constructions are fundamental to determining who benefits from such differentiation. This paper examines the use of geographical identities as a specific tool for value-adding in agricultural produce, presenting the case of specialty coffee production in South Sulawesi, Indonesia. The potential for producer-driven geographical indications compete with corporate-driven quality constructions, where the latter are able to appropriate place-related quality associations by using trademarks, vertical integration and tightly coordinated supply chain controls. An emergent politic of quality governance and ownership in global commodity chains reveals the highly restricted institutional terrain within which growers of specialty coffee might attempt to retain a higher share of the economic rent associated with quality production.  相似文献   

Predicting the future carbon budget of an upland peat catchment     

Fred Worrall  Tim Burt  John Adamson  Mark Reed  Jeff Warburton  Alona Armstrong  Martin Evans 《Climatic change》2007,85(1-2):139-158

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Understanding and managing the stressed Mexico-USA transboundary Hueco bolson aquifer in the El Paso del Norte region as a complex system     

Zhuping Sheng  Jeff Devere 《Hydrogeology Journal》2005,13(5-6):813-825

As the latest drought has swept over the southwestern United States, most local and regional water providers have had to rely on ground water to meet their water demands as surface water supplies have diminished. In areas near major population centers this situation has continued to put strain and stress on already over-drafted regional aquifers. Metropolitan centers throughout the southwestern United States, as exemplified by Las Vegas, Nevada; Phoenix and Tucson, Arizona; and El Paso, Texas, have a history of over drafting their available ground water resources. How these stressed aquifers should be managed is an urgent issue. In El Paso, Texas long-term groundwater mining in the transboundary Hueco bolson aquifer has resulted in large water level drawdowns within the basin, particularly in several well fields. This situation has promoted the intrusion of brackish water into fresh water zones, and consequently reduced the volume of fresh water stored in the aquifer. Management of this aquifer is made more complex as the water resources of the region are shared across the United States/Mexico boundary and the transboundary region continues to grow rapidly. This paper describes the current situation within the Hueco bolson due to over drafting and continued reliance on the fresh water in storage and describes how understanding the dynamics of the aquifer as a complex system can offer managerial perspectives that can be used to establish operational procedures and programs for bringing drawdowns into equilibrium, increasing the longevity of the aquifer, gradually restoring water quality, and offering the hope of utilization of the resource in a sustainable manner.

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Resumen A medida que la última sequía ha pasado ligeramente sobre el suroeste de Estados Unidos la mayoría de abastecedores locales y regionales de agua han tenido que depender del agua subterránea para satisfacer sus demandas de agua debido a que las fuentes de agua superficial han disminuido. En áreas cerca de centros poblados principales esta situación ha continuado ejerciendo presión en los ya sobre explotados acuíferos regionales. Los centros metropolitanos en todo el suroeste de Estados Unidos, por ejemplo Las Vegas, Nevada; Fénix y Tucson, Arizona; y El Paso, Texas tienen una historia de sobre explotar los recursos de agua subterránea disponibles.La gestión de estos acuíferos estresados constituye un problema urgente. En El Paso, Texas el minado de agua subterránea a largo plazo en el acuífero transnacional Hueco bolsón ha resultado en varios campos de pozos. Esta situación ha promovido la intrusión de agua salobre hacia zonas con agua fresca y reducido consecuentemente el volumen de agua fresca almacenado en el acuífero. El manejo de este acuífero se hace más complejo debido a que los recursos hídricos de la región son compartidos a través del límite Estados Unidos/México y la región transnacional continúa creciendo rápidamente. Este artículo describe la situación actual dentro del Hueco bolsón debido a la sobre explotación y continua dependencia en el agua fresca almacenada y describe como el entendimiento de la dinámica del acuífero como un sistema complejo puede ofrecer perspectivas de gestión que pueden utilizarse para establecer procedimientos operacionales y programas que conduzcan al equilibrio de los descensos, aumentando la longevidad del acuífero, gradualmente restaurando la calidad del agua, y ofreciendo la esperanza de utilizar el recurso de manera sostenible.

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Résumé Alors que la dernière sécheresse a atteint toute la partie Sud-Ouest des Etats-Unis, la plus part des distributeurs deau, locaux et régionaux, doivent sapprovisionner en eau souterraine dés lors que les niveaux des eaux de surface ont diminués. Dans les zones proches des grands centres densément peuplés, cette situation a continuée a altérée des aquifères déjà surexploités. Les centres métropolitains du Sud-Ouest des Etats-Unis (Las Vegas dans le Nevada, Phoenix et Tucson dans lArizona, El Paso au Texas) sont connus historiquement pour surexploités leurs ressources en eaux souterraines. Il devient urgent de définir un mode de gestion de ses aquifères surexploités. A El Paso dans le Texas, le minage de laquifère transfrontalier engendre un rabattement important dans le bassin, et plus particulièrement autour des zones de captage. Cette situation a induit lintrusion deaux saumâtres dans des zones deaux douces, et a par conséquent réduit le volume deau douce stockée et exploitable dans laquifère. La gestion de cet aquifère est par ailleurs complexifiée par la situation transfrontalière, dautant que la zone frontalière connaît une croissance rapide. Cet article décrit la situation actuelle dans la vallée fermée du Hueco, due au sur-rabattement et à lexploitation continue des eaux douces, et décrit comment la compréhension de laquifère, vu comme un système complexe, peut offrir des perspectives de gestion amenant à des procédures opérationnelles et à des programmes à long terme permettant de ramener à léquilibre la baisse des niveaux deau. Ainsi la longévité de laquifère sera mieux garantie, la qualité de leau sera graduellement restaurée et lutilisation de leau respectera le souci de développement durable.

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Effect of pH on photo-oxidation of dissolved organic carbon by hydroxyl radicals in a coloured, softwater stream   总被引：3，自引：1，他引：2  

Lewis A. Molot  Jeff J. Hudson  Peter J. Dillon  Sean A. Miller 《Aquatic Sciences - Research Across Boundaries》2005,67(2):189-195

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