A method for semi‐automated objective quantification of linear bedforms from multi‐scale digital elevation models     

Pierre W. Cazenave  Justin K. Dix  David O. Lambkin  Lisa C. McNeill 《地球表面变化过程与地形》2013,38(3):221-236

The increasing availability of large, detailed digital representations of the Earth's surface demands the application of objective and quantitative analyses. Given recent advances in the understanding of the mechanisms of formation of linear bedform features from a range of environments, objective measurement of their wavelength, orientation, crest and trough positions, height and asymmetry is highly desirable. These parameters are also of use when determining observation‐based parameters for use in many applications such as numerical modelling, surface classification and sediment transport pathway analysis. Here, we (i) adapt and extend extant techniques to provide a suite of semi‐automatic tools which calculate crest orientation, wavelength, height, asymmetry direction and asymmetry ratios of bedforms, and then (ii) undertake sensitivity tests on synthetic data, increasingly complex seabeds and a very large‐scale (39 000 km²) aeolian dune system. The automated results are compared with traditional, manually derived, measurements at each stage. This new approach successfully analyses different types of topographic data (from aeolian and marine environments) from a range of sources, with tens of millions of data points being processed in a semi‐automated and objective manner within minutes rather than hours or days. The results from these analyses show there is significant variability in all measurable parameters in what might otherwise be considered uniform bedform fields. For example, the dunes of the Rub' al Khali on the Arabian peninsula are shown to exhibit deviations in dimensions from global trends. Morphological and dune asymmetry analysis of the Rub' al Khali suggests parts of the sand sea may be adjusting to a changed wind regime from that during their formation 100 to 10 ka BP. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

The Multiscale TROPIcal CatchmentS critical zone observatory M-TROPICS dataset I: The Nyong River Basin,Cameroon     

Stéphane Audry  Henriette Ateba Bessa  Jean-Pierre Bedimo Bedimo  Jean-Loup Boeglin  Laurie Boithias  Jean-Jacques Braun  Bernard Dupré  Mikael Faucheux  Christelle Lagane  Jean-Christophe Maréchal  Jules Remy Ndam-Ngoupayou  Bernadette Nka Nnomo  Justin Nlozoa  Jean-Claude Ntonga  Olivier Ribolzi  Jean Riotte  Emma Rochelle-Newall  Laurent Ruiz 《水文研究》2021,35(5):e14138

Simultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modelling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented in the past 25 years, only a few are located in the humid Tropics despite the importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents, size of river systems, etc. Since 1994, weathering and erosion processes and fluxes have been investigated at both local (experimental watershed) and regional scales in the Nyong River Basin (Cameroon) which belongs to the Critical Zone Observatories network named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Cameroon are: (1) rainfall; (2) air temperature, air relative humidity, wind speed and direction, and global radiation; (3) stream and river water level; (4) pH, electrical conductivity, water temperature and suspended particulate matter (SPM) concentration; (5) major ion, alkalinity and dissolved organic carbon (DOC) concentrations. The dataset already contributed to describe the water partitioning in these tropical humid watersheds, to better understand the factors controlling chemical weathering and physical erosion in tropical ecosystems, particularly the role of organic matter. The dataset also contributed to calculate elemental weathering fluxes and saprolite production rate and to propose denudation rates on tropical cratonic landscapes. Hydrological modelling allowed quantification of the geographical water sources contributing to streamflow. DOC data were used to determine greenhouse-gas emissions and carbon budgets from African inland waters. However, long-term solute concentrations at the outlet of a small tributary of the Nyong River exhibit non-stationary behaviour over the last 26 years. The processes governing those fluctuations are not yet fully understood and might be related to changes in the hydrological regime, land-cover and land-use. The latter highlights the need for longer time-series and continued support for CZOs particularly in the humid tropics.  相似文献   

Anthropocene dwelling: Lessons from post-disaster Christchurch     

Justin Westgate 《New Zealand geographer》2020,76(1):26-38

This article takes circumstances of post-quake Christchurch as an analogue for Anthropocene emergency. I argue that Christchurch events are more than a reminder of the Earth's geologic volatility; for the Anthropocene-as-disaster, it is a prompt to contemplate what it is to dwell on unstable ground. Urban locations—towns, cities, mega-cities—are all rendered vulnerable on the surface of an unruly planet, offering no absolute refuge from planetary fluctuations. Such unsettling is deeply felt, physically and psychologically, resulting in homelessness both literal and figurative. Ensuing analysis offers insight into potential strategies for unsettled planetary dwelling to come.  相似文献   

U‐Pb zircon dating of metaigneous rocks from the Nordbreen Nappe of Svalbard’s Ny‐Friesland suggests their affinity to Northeast Greenland     

Jakub Bazarnik  Jaros&#x;aw Majka  William C. McClelland  Justin V. Strauss  Karolina Komi&#x;ska  Karsten Piepjohn  Synnve Elvevold  Zbigniew Czupyt  Tom&#x; Miku&#x; 《地学学报》2019,31(6):518-526

SIMS U‐Pb zircon dating of metaigneous rocks of the Nordbreen Nappe from the West Ny‐Friesland terrane (Eastern Basement Province of Svalbard) yields crystallization ages of 1,761 ± 4 Ma for a felsic metatuff and 1,373 ± 4 Ma for a metagabbro dyke. The Palaeoproterozoic age of the metatuff is similar to previously obtained ages for various felsic rocks from the study area, whereas the Mesoproterozoic age of the metagabbro has not been thus far documented on Svalbard. However, a similar age pattern has been reported from Northeast Greenland. Therefore, we conclude that the West Ny‐Friesland terrane can be correlated with age equivalent units of Northeast Greenland. We also explore similarities and dissimilarities between the study area and other terranes of Svalbard and speculate on regional‐scale correlations. Together, the presented new ages provide critical piercing points in palaeogeographic reconstructions of the relatively poorly understood circum‐Arctic region.  相似文献   

Stable calcium isotopic composition of meteorites and rocky planets     

Justin I. Simon  Donald J. DePaolo 《Earth and Planetary Science Letters》2010,289(3-4):457-466

New measurements of mass-dependent calcium isotope effects in meteorites, lunar and terrestrial samples show that Earth, Moon, Mars, and differentiated asteroids (e.g., 4-Vesta and the angrite and aubrite parent bodies) are indistinguishable from primitive ordinary chondritic meteorites at our current analytical resolution (± 0.07‰ SD for the ⁴⁴Ca/⁴⁰Ca ratio). In contrast, enstatite chondritic meteorites are slightly enriched in heavier calcium isotopes (ca. + 0.5‰) and primitive carbonaceous chondritic meteorites are depleted in heavier calcium isotopes (ca. ? 0.5‰). The calcium isotope effects cannot be easily ascribed to evaporation or intraplanetary differentiation processes. The isotopic variations probably survive from the earliest stages of nebular condensation, and indicate that condensation occurred under non-equilibrium (undercooled nebular gas) conditions. Some of this early high-temperature calcium isotope heterogeneity is recorded by refractory inclusions (Niederer and Papanastassiou, 1984) and survived in planetesimals, but virtually none of it survived through terrestrial planet accretion. The new calcium isotope data suggest that ordinary chondrites are representative of the bulk of the refractory materials that formed the terrestrial planets; enstatite and carbonaceous chondrites are not. The enrichment of light calcium isotopes in bulk carbonaceous chondrites implies that their compositions are not fully representative of the solar nebula condensable fraction.  相似文献   

Discrimination of Nuclear Explosions against Civilian Sources Based on Atmospheric Xenon Isotopic Activity Ratios     

Martin B. Kalinowski  Anders Axelsson  Marc Bean  Xavier Blanchard  Theodore W. Bowyer  Guy Brachet  Simon Hebel  Justin I. McIntyre  Jana Peters  Christoph Pistner  Maria Raith  Anders Ringbom  Paul R. J. Saey  Clemens Schlosser  Trevor J. Stocki  Thomas Taffary  R. Kurt Ungar 《Pure and Applied Geophysics》2010,167(4-5):517-539

A global monitoring system for atmospheric xenon radioactivity is being established as part of the International Monitoring System that will verify compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) once the treaty has entered into force. This paper studies isotopic activity ratios to support the interpretation of observed atmospheric concentrations of ¹³⁵Xe, ^133mXe, ¹³³Xe and ^131mXe. The goal is to distinguish nuclear explosion sources from civilian releases. Simulations of nuclear explosions and reactors, empirical data for both test and reactor releases as well as observations by measurement stations of the International Noble Gas Experiment (INGE) are used to provide a proof of concept for the isotopic ratio based method for source discrimination.  相似文献   

Creating a GIS-based model of marine debris "hot spots" to improve efficiency of a lobster trap debris removal program     

Martens J  Huntington BE 《Marine pollution bulletin》2012,64(5):949-955

Debris removal programs are combatting the accumulation of derelict fishing gear and other debris in marine habitats. We analyzed 5 years of lobster trap debris removal data in Biscayne National Park, Florida to assess removal efficiency and develop spatially-explicit mapping tools to guide future removals. We generated and validated debris "hot spots" maps that combined remotely-sensed data (i.e. benthic habitat type and bathymetry) with 862 locations of previous debris collection. Our hot spot models spatially depict regions of likely debris accumulation, reducing the search area by 95% (from 332 km(2) to 18 km(2)) and encompassing 100% of the validation sites. Our analyses indicate removal contractors using sub-surface towed divers enhanced debris recovery. Additionally, the quantity of debris removed did not decrease with increased efforts, suggesting that debris supply in situ exceeds removal efforts. We conclude with the importance of coupling analysis of ongoing debris removal programs with GIS technology to improve removal efforts.  相似文献   

Marine biosecurity: The importance of awareness, support and cooperation in managing a successful incursion response     

Piola RF  McDonald JI 《Marine pollution bulletin》2012,64(9):1766-1773

Shipping is almost certainly the most prevalent human-mediated transport vector for non-indigenous species (NIS) within the marine environment. The Royal Australian Navy (RAN) has long acknowledged the importance of sound environmental management and in recent years has taken a proactive approach to addressing risks associated with marine biosecurity. primarily as a result of biofouling on Navy vessel returning from overseas operations. This paper describes two case studies that highlight the effectiveness of the RAN marine biosecurity management framework in identifying an unwanted marine species on Navy vessels, and the successful biosecurity management program that ensued. In particular, the early detection and identification of a suspect NIS, the quick response to the discovery and the collaborative approach adopted between the RAN and the Government regulatory agency (Western Australian Department of Fisheries) charged with coordinating the incursion response serves as a model for how future incursion responses should be reported and managed.  相似文献   

A model of diffuse Galactic radio emission from 10 MHz to 100 GHz     

Angélica de Oliveira-Costa  Max Tegmark  B. M. Gaensler  Justin Jonas  T. L. Landecker  Patricia Reich 《Monthly notices of the Royal Astronomical Society》2008,388(1):247-260

Understanding diffuse Galactic radio emission is interesting both in its own right and for minimizing foreground contamination of cosmological measurements. cosmic microwave background experiments have focused on frequencies ≳10 GHz, whereas 21-cm tomography of the high-redshift universe will mainly focus on ≲0.2 GHz, for which less is currently known about Galactic emission. Motivated by this, we present a global sky model derived from all publicly available total power large-area radio surveys, digitized with optical character recognition when necessary and compiled into a uniform format, as well as the new Villa Elisa data extending the 1.42-GHz map to the entire sky. We quantify statistical and systematic uncertainties in these surveys by comparing them with various global multifrequency model fits. We find that a principal component based model with only three components can fit the 11 most accurate data sets (at 10, 22, 45 and 408 MHz and 1.42, 2.326, 23, 33, 41, 61, 94 GHz) to an accuracy around 1–10 per cent depending on frequency and sky region. Both our data compilation and our software returning a predicted all-sky map at any frequency from 10 MHz to 100 GHz are publicly available at http://space.mit.edu/home/angelica/gsm .  相似文献   

Development and experimental evaluation of a passive gap damper device to prevent pounding in base‐isolated structures          下载免费PDF全文

Taylor A. Rawlinson  Justin D. Marshall  Keri L. Ryan  Hamed Zargar 《地震工程与结构动力学》2015,44(11):1661-1675

Studies have shown the effectiveness of providing supplemental energy dissipation in base‐isolated structures to reduce displacements at the isolation level. A previous analytical study demonstrated the benefits of providing this energy dissipation at a specified gap larger than the design displacement. The gap before engagement allows the base isolation system to meet performance criteria in varying levels of ground excitation. Use of this ‘gap damper’ device eliminates undesirable effects often exhibited with large amounts of supplemental damping at lower intensity motions. Using results from an analytical study, the primary purpose of this research was to develop devices for practical implementation. Development of the devices demanded simplicity, feasibility, economy, and reliability to be an effective option in building design and construction. Multiple designs were proposed, and a final design was chosen based on selection criteria and finite element analyses. The device was designed and tested in Auburn University's Structural Research Lab. Experimental results were compared with theoretical models to verify behavior and make necessary adjustments for a shake table experiment. The design parameters were selected to accommodate re‐use of the device for the shake table test. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献