Extracting water-related features using reflectance data and principal component analysis of Landsat images     

Boglárka Balázs  Tibor Bíró  Gareth Dyke  Sudhir Kumar Singh 《水文科学杂志》2018,63(2):269-284

This study aimed to map water features using a Landsat image rather than traditional land cover. We involved the original bands, spectral indices and principal components (PCs) of a principal component analysis (PCA) as input data, and performed random forest (RF) and support vector machine (SVM) classification with water, saturated soil and non-water categories. The aim was to compare the efficiency of the results based on various input data. Original bands provided 93% overall accuracy (OA) and bands 4–5–7 were the most informative in this analysis. Except for MNDWI (modified normalized differenced water index, with 98% OA), the performance of all water indices was between 60 and 70% (OA). The PCA-based approach conducted on the original bands resulted in the most accurate identification of all classes (with only 1% error in the case of water bodies). We therefore show that both water bodies and saturated soils can be identified successfully using this approach.  相似文献   

Estimation of commercial diamond grades based on microdiamonds: a case study of the Koidu diamond mine,Sierra Leone     

Nowicki  Tom  Garlick  Gareth  Webb  Kimberley  Van Eeden  Miles 《Mineralogy and Petrology》2018,112(2):685-695

This paper documents the application of a microdiamond-based approach to the estimation of diamond grade in the Pipe 1 kimberlite at the Koidu mine in Sierra Leone. A geological model of Pipe 1 was constructed to represent the distribution and volume of the dominant kimberlite units within the pipe. Bulk samples, along with representative microdiamond samples, were collected from these units at surface and were used to define the ratio between microdiamond stone frequency (+212 μm stones per kilogram) and recoverable macrodiamond grade (+1.2 mm carats per tonne; 1 carat = 0.2 g). These ratios were applied to a comprehensive, spatially representative microdiamond sample dataset and were combined with a spatial model of country-rock xenolith dilution within the pipe to estimate +1.2 mm recoverable grades. The resource estimate was reconciled with subsequent production results in the elevation range 160 to 100 m above sea level. Production results for each of the six 10 m benches covering this elevation range were compared to the estimated average grades for these zones in the pipe. For the five cases where most of the kimberlite mass on a given bench is represented in the production data, the results show a maximum discrepancy of 6% between predicted and reported production grade with no indication of any consistent bias. This indicates that, when supported by a sound geological model and suitable microdiamond and macrodiamond data, the microdiamond-based estimation approach can provide reliable constraints on macrodiamond grade, even in the case of geologically complex bodies such as Koidu Pipe 1.

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Enhanced bed load sediment transport by unsteady flows in a degrading channel     

Zhijing Li  Honglu Qian  Zhixian Cao  Huaihan Liu  Gareth Pender  Penghui Hu 《国际泥沙研究》2018,33(3):327-339

Laboratory flume experiments were done to investigate bed load sediment transport by both steady and unsteady flows in a degrading channel. The bed, respectively composed of uniform sand, uniform gravel, or sand-gravel mixtures, always undergoes bulk degradation. It is found that both uniform and non-uniform bed load transport is enhanced greatly by unsteady flows as compared to their volume-equivalent steady flows. This enhancement effect is evaluated by means of an enhancement factor, which is shown to be larger with a coarser bed and lower discharges. Also, the fractional transport rates of gravel and sand in non-uniform sand-gravel mixtures are compared with their uniform counterparts under both steady and unsteady flows. The sand is found to be able to greatly promote the transport of gravel, whilst the gravel considerably hinders the transport of sand. Particularly, the promoting and hindering impacts are more pronounced at lower discharges and tend to be weakened by flow unsteadiness.  相似文献   

Combining shock barometry with numerical modeling: Insights into complex crater formation—The example of the Siljan impact structure (Sweden)          下载免费PDF全文

Sanna Holm‐Alwmark  Auriol S. P. Rae  Ludovic Ferrière  Carl Alwmark  Gareth S. Collins 《Meteoritics & planetary science》2017,52(12):2521-2549

Siljan, central Sweden, is the largest known impact structure in Europe. It was formed at about 380 Ma, in the late Devonian period. The structure has been heavily eroded to a level originally located underneath the crater floor, and to date, important questions about the original size and morphology of Siljan remain unanswered. Here we present the results of a shock barometry study of quartz‐bearing surface and drill core samples combined with numerical modeling using iSALE. The investigated 13 bedrock granitoid samples show that the recorded shock pressure decreases with increasing depth from 15 to 20 GPa near the (present) surface, to 10–15 GPa at 600 m depth. A best‐fit model that is consistent with observational constraints relating to the present size of the structure, the location of the downfaulted sediments, and the observed surface and vertical shock barometry profiles is presented. The best‐fit model results in a final crater (rim‐to‐rim) diameter of ~65 km. According to our simulations, the original Siljan impact structure would have been a peak‐ring crater. Siljan was formed in a mixed target of Paleozoic sedimentary rocks overlaying crystalline basement. Our modeling suggests that, at the time of impact, the sedimentary sequence was approximately 3 km thick. Since then, there has been around 4 km of erosion of the structure.  相似文献   

Analysis of a regional change in the sign of the SAM�Ctemperature relationship in Antarctica     

Gareth J. Marshall  Stefano Di Battista  Sushant S. Naik  Meloth Thamban 《Climate Dynamics》2011,36(1-2):277-287

This study examines regional atmospheric circulation changes associated with a reversal in the sign of the relationship between the Southern Annular Mode (SAM) and near-surface temperatures at Halley station, East Antarctica, during the 1980s. We show that the key factor affecting the regional SAM?Ctemperature relationship (STR) is the relative magnitude of two climatological low pressure centres to the west and east of the area, which determines the source region of air masses advected into the locality. The principal difference affecting the STR is shown to be a trend towards a significantly weaker climatological low (higher pressure) at ~20°E during a positive phase of the SAM. Specifically, it is variations in the phase and magnitude of the wave number three patterns of atmospheric circulation, the non-annular component of the SAM, which are the principal factors governing the regional STR. A similar reversal is observed in the sign of the correlation between the SAM and oxygen-isotope values from an ice core located some 1,200?km east of Halley. This relationship is examined throughout the 20th Century, by comparing the isotope data to SAM reconstructions, and demonstrates marked decadal variability. Thus, these data suggest that switches in the STR are more likely to reflect natural variability in the long-wave patterns over the Southern Ocean rather than the influence of an anthropogenic forcing. This finding is important when considering the potential utility of Antarctic isotope data as a proxy for the SAM.  相似文献   

Climate justice and global cities: Mapping the emerging discourses     

Harriet Bulkeley  JoAnn Carmin  Vanesa Castán Broto  Gareth A.S. Edwards  Sara Fuller 《Global Environmental Change》2013,23(5):914-925

Ever since climate change came to be a matter of political concern, questions of justice have been at the forefront of academic and policy debates in the international arena. Curiously, as attention has shifted to other sites and scales of climate change politics matters of justice have tended to be neglected. In this paper, we examine how discourses of justice are emerging within urban responses to climate change. Drawing on a database of initiatives taking place in 100 global cities and qualitative case-study research in Philadelphia, Quito and Toronto, we examine how notions of distributive and procedural justice are articulated in climate change projects and plans in relation to both adaptation and mitigation. We find that there is limited explicit concern with justice at the urban level. However, where discourses of justice are evident there are important differences emerging between urban responses to adaptation and mitigation, and between those in the north and in the south. Adaptation responses tend to stress the distribution of ‘rights’ to protection, although those in the South also stress the importance of procedural justice. Mitigation responses also stress ‘rights’ to the benefits of responding to climate change, with limited concern for ‘responsibilities’ or for procedural justice. Intriguingly, while adaptation responses tend to stress the rights of individuals, we also find discourses of collective rights emerging in relation to mitigation.  相似文献   

The Political Economy of Sustainable Energy – By Catherine Mitchell     

Gareth  Powells 《The Geographical journal》2009,175(4):315-316

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Well-balanced numerical modelling of non-uniform sediment transport in alluvial rivers     

Honglu Qian  Zhixian Cao  Gareth Pender  Huaihan Liu  Peng Hu 《国际泥沙研究》2015,(2):117-130

The last two decades have witnessed the development and application of well-balanced numerical models for shallow flows in natural rivers.However,until now there have been no such models for flows with non-uniform sediment transport.This paper presents a 1D well-balanced model to simulate flows and non-capacity transport of non-uniform sediment in alluvial rivers.The active layer formulation is adopted to resolve the change of bed sediment composition.In the framework of the finite volume Slope Llmiter Centred(SLIC) scheme,a surface gradient method is incorporated to attain well-balanced solutions to the governing equations.The proposed model is tested against typical cases with irregular topography,including the refilling of dredged trenches,aggradation due to sediment overloading and flood flow due to landslide dam failure.The agreement between the computed results and measured data is encouraging.Compared to a non-well-balanced model,the well-balanced model features improved performance in reproducing stage,velocity and bed deformation.It should find general applications for non-uniform sediment transport modelling in alluvial rivers,especially in mountain areas where the bed topography is mostly irregular.  相似文献   

Compositional changes in soil water and runoff water following managed burning on a UK upland blanket bog     

Gareth D. Clay  Fred Worrall  Evan D.G. Fraser 《Journal of Hydrology》2010,380(1-2):135-145

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Modeling patterns of coral bleaching at a remote Central Pacific atoll     

Gareth J. Williams  Ingrid S. Knapp  Simon K. Davy 《Marine pollution bulletin》2010,60(9):1467-1476

A mild bleaching event (9.2% prevalence) at Palmyra Atoll occurred in response to the 2009 ENSO, when mean water temperature reached 29.8-30.1 °C. Prevalence among both abundant and sparse taxa varied with no clear pattern in susceptibility relating to coral morphology. Seven taxon-specific models showed that turbidity exacerbated while prior exposure to higher background temperatures alleviated bleaching, with these predictors explaining an average 16.3% and 11.5% variation in prevalence patterns, respectively. Positive associations occurred between bleaching prevalence and both immediate temperature during the bleaching event (average 8.4% variation explained) and increased sand cover (average 3.7%). Despite these associations, mean unexplained variation in prevalence equalled 59%. Lower bleaching prevalence in areas experiencing higher background temperatures suggests acclimation to temperature stress among several coral genera, while WWII modifications may still be impacting the reefs via shoreline sediment re-distribution and increased turbidity, exacerbating coral bleaching susceptibility during periods of high temperature stress.  相似文献