Derek Hall,Philip Hirsch and Tania Murray Li,Powers of Exclusion: Land Dilemmas in Southeast Asia     

Carl Middleton 《Singapore journal of tropical geography》2012,33(2):278-281

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Boosting for Mineral Prospectivity Modeling: A New GIS Toolbox     

Brandmeier  Melanie  Cabrera Zamora  Irving Gibran  Nykänen  Vesa  Middleton  Maarit 《Natural Resources Research》2020,29(1):71-88

With an increasing demand for raw materials, predictive models that support successful mineral exploration targeting are of great importance. We evaluated different machine learning techniques with an emphasis on boosting algorithms and implemented them in an ArcGIS toolbox. Performance was tested on an exploration dataset from the Iberian Pyrite Belt (IPB) with respect to accuracy, performance, stability, and robustness. Boosting algorithms are ensemble methods used in supervised learning for regression and classification. They combine weak classifiers, i.e., classifiers that perform slightly better than random guessing to obtain robust classifiers. Each time a weak learner is added; the learning set is reweighted to give more importance to misclassified samples. Our test area, the IPB, is one of the oldest mining districts in the world and hosts giant volcanic-hosted massive sulfide (VMS) deposits. The spatial density of ore deposits, as well as the size and tonnage, makes the area unique, and due to the high data availability and number of known deposits, well-suited for testing machine learning algorithms. We combined several geophysical datasets, as well as layers derived from geological maps as predictors of the presence or absence of VMS deposits. Boosting algorithms such as BrownBoost and Adaboost were tested and compared to Logistic Regression (LR), Random Forests (RF) and Support Vector machines (SVM) in several experiments. We found performance results relatively similar, especially to BrownBoost, which slightly outperformed LR and SVM with respective accuracies of 0.96 compared to 0.89 and 0.93. Data augmentation by perturbing deposit location led to a 7% improvement in results. Variations in the split ratio of training and test data led to a reduction in the accuracy of the prediction result with relative stability occurring at a critical point at around 26 training samples out of 130 total samples. When lower numbers of training data were introduced accuracy dropped significantly. In comparison with other machine learning methods, Adaboost is user-friendly due to relatively short training and prediction times, the low likelihood of overfitting and the reduced number of hyperparameters for optimization. Boosting algorithms gave high predictive accuracies, making them a potential data-driven alternative for regional scale and/or brownfields mineral exploration.

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High temperature gas–solid reactions in calc–silicate Cu–Au skarn formation; Ertsberg,Papua Province,Indonesia     

Richard?W.?HenleyEmail authorView author&#;s OrcID profile  Frank?J.?Brink  Penelope?L.?King  Clyde?Leys  Jibamitra?Ganguly  Terrance?Mernagh  Jill?Middleton  Christian?J.?Renggli  Melanie?Sieber  Ulrike?Troitzsch  Michael?Turner 《Contributions to Mineralogy and Petrology》2017,172(11-12):106

The 2.7–3 Ma Ertsberg East Skarn System (Indonesia), adjacent to the giant Grasberg Porphyry Copper deposit, is part of the world’s largest system of Cu–Au skarn deposits. Published fluid inclusion and stable isotope data show that it formed through the flux of magma-derived fluid through contact metamorphosed carbonate rock sequences at temperatures well above 600° C and pressures of less than 50 MPa. Under these conditions, the fluid has very low density and the properties of a gas. Combining a range of micro-analytical techniques, high-resolution QEMSCAN mineral mapping and computer-assisted X-ray micro-tomography, an array of coupled gas–solid reactions may be identified that controlled reactive mass transfer through the ~ 1 km³ hydrothermal skarn system. Vacancy-driven mineral chemisorption reactions are identified as a new type of reactive transport process for high-temperature skarn alteration. These gas–solid reactions are maintained by the interaction of unsatisfied bonds on mineral surfaces and dipolar gas-phase reactants such as SO₂ and HCl that are continuously supplied through open fractures and intergranular diffusion. Principal reactions are (a) incongruent dissolution of almandine-grossular to andradite and anorthite (an alteration mineral not previously recognized at Ertsberg), and (b) sulfation of anorthite to anhydrite. These sulfation reactions also generate reduced sulfur with consequent co-deposition of metal sulfides. Diopside undergoes similar reactions with deposition of Fe-enriched pyroxene in crypto-veins and vein selvedges. The loss of calcium from contact metamorphic garnet to form vein anhydrite necessarily results in Fe-enrichment of wallrock, and does not require Fe-addition from a vein fluid as is commonly assumed.  相似文献   

Imaging spectroscopy in soil-water based site suitability assessment for artificial regeneration to Scots pine     

Maarit Middleton  Paavo Nrhi  Raimo Sutinen 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(3):287-297

In a humid northern boreal climate, the success rate of artificial regeneration to Scots pine (Pinus sylvestris L.) can be improved by including a soil water content (SWC) based assessment of site suitability in the reforestation planning process. This paper introduces an application of airborne visible-near-infrared imaging spectroscopic data to identify suitable subregions of forest compartments for the low SWC-tolerant Scots pine. The spatial patterns of understorey plant species communities, recorded by the AISA (Airborne Imaging Spectrometer for Applications) sensor, were demonstrated to be dependant on the underlying SWC. According to the nonmetric multidimensional scaling and correlation results twelve understorey species were found to be most abundant on sites with high soil SWCs. The abundance of bare soil, rocks and abundance of more than ten species indicated low soil SWCs. The spatial patterns of understorey are attributed to time-stability of the underlying SWC patterns. A supervised artificial neural network (radial basis functional link network, probabilistic neural network) approach was taken to classify AISA imaging spectrometer data with dielectric (as a measure volumetric SWC) ground referencing into regimes suitable and unsuitable for Scots pine. The accuracy assessment with receiver operating characteristics curves demonstrated a maximum of 74.1% area under the curve values which indicated moderate success of the NN modelling. The results signified the importance of the training set’s quality, adequate quantity (>2.43 points/ha) and NN algorithm selection over the NN algorithm training parameter optimization to perfection. This methodology for the analysis of site suitability of Scots pine can be recommended, especially when artificial regeneration of former mixed wood Norway spruce (Picea abies L. Karst) - downy birch (Betula pubenscens Ehrh.) stands is being considered, so that artificially regenerated areas to Scots pine can be optimized for forestry purposes.  相似文献   

Detecting significant sediment motion in a laboratory flume using digital video image analysis     

J. Brasington  R. Middleton  L. E. Frostick  B. J. Murphy 《地球表面变化过程与地形》2000,25(2):191-196

A video analysis method for monitoring sediment transport and sorting processes in a laboratory flume is presented. Video taken through the glass side‐wall of a laboratory flume is captured using a digital CCD (charge‐coupled device) camera and significant movements between individual frames are detected using image analysis. This method involves direct subtraction of the brightness numbers of pixels in sequential video frames, followed by thresholding to produce binarized images of significant change, above the inherent level of system noise. Experimental results showing dilation of a gravel framework and rapid infiltration of fines just prior to entrainment are discussed. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Dating of paleolandslides in western Finnish Lapland          下载免费PDF全文

Antti E.K. Ojala  Mira Markovaara‐Koivisto  Maarit Middleton  Timo Ruskeeniemi  Jussi Mattila  Raimo Sutinen 《地球表面变化过程与地形》2018,43(11):2449-2462

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Geomorphological evidence of paleoseismicity: Surficial and underground structures of Pasmajärvi postglacial fault     

Mira Markovaara-Koivisto  Antti E.K. Ojala  Jussi Mattila  Ilmo Kukkonen  Ilkka Aro  Arto Pullinen  Pekka Hänninen  Maarit Middleton  Aleksi Sutinen  Juha Majaniemi  Timo Ruskeeniemi  Raimo Sutinen 《地球表面变化过程与地形》2020,45(12):3011-3024

The cyclic nature of glaciations and related postglacial faulting represents a risk for the deep geological disposal of spent nuclear fuel in areas likely to be affected by future glaciations. Seismic history was therefore studied by means of detecting geomorphological structures on airborne laser scanning digital elevation models and underground by excavating in an esker and trenching across a postglacial fault located in northern Fennoscandia. OLS dating and assessing the geomorphological structures was used for timing of the seismic history. The results suggest that the faulting of different segments in the Pasmajärvi complex is due to at least two late Weichselian events, which probably occurred both subglacially and postglacially. The most reliable input for the moment magnitude estimates was vertical slip profiles, and therefore these estimates (M_W ≈ 6.4–6.9) are suggested. © 2020 John Wiley & Sons, Ltd.  相似文献   

Cosmogenic nuclides in core samples of the Chico L6 chondrite: Evidence for irradiation under high shielding     

D. H. Garrison  D. D. Bogard  A. A. Albrecht  S. Vogt  G. F. Herzog  J. Klein  D. Fink  B. Dezfouly-Arjomandy  R. Middleton 《Meteoritics & planetary science》1992,27(4):371-381

Abstract— Core samples were obtained from various locations of the ～ 105-kg Chico, NM, L6 chondrite in order to study the effects of large shielding on the production rates of cosmic-ray-produced nuclides. Relations between measured abundances of cosmogenic nuclides (¹⁰Be, ²⁶Al, and stable isotopes of He, Ne, and Ar) and the cosmogenic ²²Ne/²¹Ne ratio were determined and compared with recent model predictions of production rates. The measured ²²Ne/²¹Ne ratios (1.06-1.08) and significant variations observed in concentrations of cosmogenic ²¹Ne and ³He suggest an ～40-cm shielding gradient across Chico and irradiation within a large object (> 100-cm radius). Noble gas data indicate that Chico experienced greater shielding than chondrites Knyahinya or Keyes and similar to Jilin. Values of ¹⁰Be (average = 20.7 dpm/kg) and ²⁶Al (average = 71.1 dpm/kg) are nearly constant, however, and show no correlation with either ²²Ne/²¹Ne or ²¹Ne. Activities of ¹⁰Be and ²⁶Al suggest irradiation in a smaller object (～40–80 cm radius). The ²⁶Al activity and the ²⁶Al/¹⁰Be ratio (average value = 3.42) are both significantly larger than values for most other chondrites. These results could indicate a two-stage irradiation with t₁ ～ 104 Ma and t₂ ～ 4 Ma and a second-stage body the size of Knyahinya. The single stage, ¹⁰Be/²¹Ne exposure age for Chico is 65 Ma. The ²²Ne/²¹Ne ratio apparently becomes insensitive to shielding for objects the size of Chico. No substantial evidence exists for chondrites with ²²Ne/²¹Ne ratios significantly less than ～ 1.055.  相似文献   

Earth system curator: metadata infrastructure for climate modeling     

Rocky Dunlap  Leo Mark  Spencer Rugaber  V. Balaji  Julien Chastang  Luca Cinquini  Cecelia DeLuca  Don Middleton  Sylvia Murphy 《Earth Science Informatics》2008,1(3-4):131-149

The Earth System Curator is a National Science Foundation sponsored project developing a metadata formalism for describing the digital resources used in climate simulations. The primary motivating observation of the project is that a simulation/model’s source code plus the configuration parameters required for a model run are a compact representation of the dataset generated when the model is executed. The end goal of the project is a convergence of models and data where both resources are accessed uniformly from a single registry. In this paper we review the current metadata landscape of the climate modeling community, present our work on developing a metadata formalism for describing climate models, and reflect on technical challenges we have faced that require new research in the area of Earth Science Informatics.  相似文献   

New insights into biological influence on the geochemistry of freshwater carbonate deposits   总被引：2，自引：0，他引：2  

M. Rogerson  H.M. Pedley  R. Middleton 《Geochimica et cosmochimica acta》2008,72(20):4976-4987

Ambient temperature freshwater carbonates (“tufas”) have outstanding potential as palaeoclimate archives. However, it has proven difficult to constrain the behaviour of the geochemical parameters on which important proxy systems rely. Current thinking on the development of trace element ratios in tufa rests upon an assumption of precipitation driven by degassing of CO₂, with the final precipitate being in equilibrium with ambient river water. This study provides evidence that although supersaturation is largely regulated by degassing, precipitation in sterile flowing systems does not occur throughout the air-water interface, but only at lines of intersection between this interface and a solid surface. Precipitation at the bottom, as is normal in river sites, is not found to occur. However, when benthic microbial communities (“biofilms”) are present, extensive precipitation does occur within them in preference and/or addition to that at the air-water interface. Precipitation is therefore not purely a consequence of degassing, and some microbiological influence is necessary to generate precipitates analogous to nature.We further investigate whether these biofilms alter the behaviour of trace elements within tufa systems, in addition to modulating the sites and mechanisms of precipitation, via a series of experiments. Biofilms are shown to accumulate large inventories of calcium and other dissolved ions (Ba, Sr, and Mg), and we demonstrate that this process is chemoselective in favour of ions with low charge densities. These observations have consequences for interpretation of trace element records from tufas based on an assumption of equilibrium with river water, and also for other carbonate deposits associated with biofilm activity (travertines, marine stromatolites, lacustrine and soil carbonates, speleothems). Conversely, our study provides new insight into the reasons for discrepancy of tufa Mg/Ca ratios from expectation, and thus provides encouragement for the potential of Mg/Ca palaeothermometry in freshwater carbonate systems.  相似文献