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91.
Digital elevation models (DEMs) are a necessary dataset for modelling the Earth’s surface; however, all DEMs contain error. Researchers can reduce this error using DEM fusion techniques since numerous DEMs can be available for a region. However, the use of a clustering algorithm in DEM fusion has not been previously reported. In this study a new DEM fusion algorithm based on a clustering approach that works on multiple DEMs to exploit consistency in the estimates as indicators of accuracy and precision is presented. The fusion approach includes slope and elevation thresholding, k-means clustering of the elevation estimates at each cell location, as well as filtering and smoothing of the fusion product. Corroboration of the input DEMs, and the products of each step of the fusion algorithm, with a higher accuracy reference DEM enabled a detailed analysis of the effectiveness of the DEM fusion algorithm. The main findings of the research were: the k-means clustering of the elevations reduced the precision which also impacted the overall accuracy of the estimates; the number of final cluster members and the standard deviation of elevations before clustering both had a strong relationship to the error in the k-means estimates. 相似文献
92.
The goal of automated three dimensional measurement of arbitrary objects using photogrammetric methods is a long way from being achieved, but significant progress is being made. However, automated measurement of small objects using inexpensive CCD cameras and frame grabbers is becoming increasingly common. A number of such systems have been developed both for commercial use and for academic research. It is within this latter context that a system to measure objects within a controlled environment has been developed at City University. The objective of the research is not only to produce a flexible measuring system for use in online inspection, but also to address many of the fundamental problems that hinder three dimensional measurement outside a controlled environment. 相似文献
93.
Electron spin resonance (ESR) spectroscopy, thermal analysis and X-ray diffraction (XRD) analysis are used to study the mode of incorporation of a wide range of impurity ions (up to 1% Ni2+, Sr2+, Cd2+, Mg2+, Cu2+, Fe2+, Zn2+, Pb2+, Mn2+ and Ba2+) in calcites synthesised in aqueous solutions. It is shown that when certain impurity ions are incorporated in these calcites they become concentrated, together with other trace elements such as Mn2+, into hitherto unsuspected trace phases. The important conclusion is drawn that unless the scavenging of trace elements by these phases can be avoided or corrected for, any calcite—liquid partition coefficients measured may have limited significance. ESR spectroscopy has revealed the intense strain common in calcites grown by different methods, whilst thermal analysis suggested that such strain may significantly alter the thermodynamic properties of these calcites. ESR spectroscopic analysis of aragonites synthesised by methods previously reported in the literature has revealed the common occurrence of trace calcite at concentrations below the XRD detection limit and proves the tendency of this calcite to scavenge trace Mn. Using ESR spectroscopy to monitor trace calcite levels and structural imperfections in synthetic aragonites, the urea hydrolysis technique is modified to provide a method for the synthesis of high-purity strain-free aragonite available for experimental studies. 相似文献
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96.
Colleen C. Hiner 《The Professional geographer》2016,68(4):520-532
As examinations of the rural–urban interface move beyond a focus on the rural or urban fringe as a location and move toward examining the patterns and processes that both divide and link rural and urban places, a broader (re)conceptualization of the rural–urban interface becomes increasingly important. Thus far the question of boundaries and interfaces between so-called urban and rural locales has mostly revolved around where and when such boundaries occur (including significant coverage of the differences and conflicts between urban vs. rural people), rather than asking what physical or social functions are being served by the rural–urban interface itself. In response, I (re)frame the rural–urban interface not only as a boundary between two distinct spaces but also as a conduit, a place of exchange, and a flux point between them. Using a particular case of contested ecologies in the exurban Sierra Nevada foothills of California, I (re)conceptualize the rural–urban interface as meaning, model, and metaphor (MMM), situating contrasting people and places in an ongoing negotiation of place and environmental meaning along the (ex)urbanizing edge. Although the differences between rural and urban are increasingly unclear, the division continues to be compelling from environmental and sociopolitical standpoints. I argue that (perceived) boundaries are instrumental in understanding physical–material change and for mitigating social conflicts occurring across them. As such, attention to the patterns, processes, and flows that connect or separate rural and urban areas is critical to forging effective and long-lasting solutions to contemporary social, economic, and environmental problems. 相似文献
97.
The use of CCD cameras for digital photogrammetry has only slowly been taken up by the photogrammetric community. However, the pace of change is quickening with better understanding and cheaper equipment. Recently a decision was made to start some research into close range three dimensional digital measurement. The overall objective was to develop a low cost system for the automated measurement of small industrial objects. This shorter contribution describes the initial stages of this work. 相似文献
98.
Luther III George W. Karolewski Jennifer S. Sutherland Kevin M. Hansel Colleen M. Wankel Scott D. 《Aquatic Geochemistry》2021,27(3):207-220
Aquatic Geochemistry - Given their environmental abundances, it has been long hypothesized that geochemical interactions between reactive forms of manganese and nitrogen may play important roles in... 相似文献
99.
Sarah McMullan Denis Vida Hadrien A. R. Devillepoix Jim Rowe Luke Daly Ashley J. King Martin Cupák Robert M. Howie Eleanor K. Sansom Patrick Shober Martin C. Towner Seamus Anderson Luke McFadden Jana Horák Andrew R. D. Smedley Katherine H. Joy Alan Shuttleworth Francois Colas Brigitte Zanda Áine C. O'Brien Ian McMullan Clive Shaw Adam Suttle Martin D. Suttle John S. Young Peter Campbell-Burns Richard Kacerek Richard Bassom Steve Bosley Richard Fleet Dave Jones Mark McIntyre Nick James Derek Robson Paul Dickinson Philip A. Bland Gareth S. Collins 《Meteoritics & planetary science》2024,59(5):927-947
On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s−1). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures. 相似文献
100.
Scientists and water users are concerned about the potential impact on water resources, particularly during low-flow periods, of freshwater withdrawals for hydraulic fracturing (fracking). Therefore, the objective of this paper is to assess the potential impact of hydraulic fracturing on water resources in the Muskingum watershed of Eastern Ohio, USA, especially due to the trend of increased withdrawals for hydraulic fracking during drought years. The Statistical Downscaling Model (SDSM) was used to generate 30 years of plausible future daily weather series in order to capture the possible dry periods. The data generated were incorporated in the Soil and Water Assessment Tool (SWAT) to examine the level of impact due to fracking at various scales. Analyses showed that water withdrawal due to hydraulic fracking had a noticeable impact, especially during low-flow periods. Clear changes in the 7-day minimum flows were detected among baseline, current and future scenarios when the worst-case scenario was implemented. The headwater streams in the sub-watersheds were highly affected, with significant decrease in 7-day low flows. The flow alteration in hydrologically-based (7Q10, i.e. 7-day 10-year low flow) or biologically-based (4B3 and 1B3) design flows due to hydraulic fracking increased with decrease in the drainage area, indicating that the relative impact may not be as great for higher order streams. Nevertheless, change in the annual mean flow was limited to 10%. 相似文献