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11.
Use of GIS layers, in which the cell values represent fuzzy membership variables, is an effective method of combining subjective geological knowledge with empirical data in a neural network approach to mineral-prospectivity mapping. In this study, multilayer perceptron (MLP), neural networks are used to combine up to 17 regional exploration variables to predict the potential for orogenic gold deposits in the form of prospectivity maps in the Archean Kalgoorlie Terrane of Western Australia. Two types of fuzzy membership layers are used. In the first type of layer, the statistical relationships between known gold deposits and variables in the GIS thematic layer are used to determine fuzzy membership values. For example, GIS layers depicting solid geology and rock-type combinations of categorical data at the nearest lithological boundary for each cell are converted to fuzzy membership layers representing favorable lithologies and favorable lithological boundaries, respectively. This type of fuzzy-membership input is a useful alternative to the 1-of-N coding used for categorical inputs, particularly if there are a large number of classes. Rheological contrast at lithological boundaries is modeled using a second type of fuzzy membership layer, in which the assignment of fuzzy membership value, although based on geological field data, is subjective. The methods used here could be applied to a large range of subjective data (e.g., favorability of tectonic environment, host stratigraphy, or reactivation along major faults) currently used in regional exploration programs, but which normally would not be included as inputs in an empirical neural network approach. 相似文献
12.
《The Journal of geography》2012,111(3):164-171
Abstract As computers become commonplace in the nation's schools, interactive maps are finding their way into the geography classroom. Students can use electronic atlases to access information as well as use authoring software to produce their own interactive maps. Does this change in media correspond to better geography education for our children? This article addresses whether using interactive maps for gathering and presenting information can have a positive influence on learning geography content. A two-week experiment was conducted in five 7th grade classrooms. Students in four of the classes researched and produced map products using both traditional and computer-assisted techniques. The fifth class was a control group. A pretest and two post-tests were given to quantitatively assess student learning after each project. Also, students were given a qualitative questionnaire to determine their attitude towards the different techniques. Quantitative results of the study indicate that there was no significant difference in student post-test performance after using each of the techniques, but qualitative results suggest that students prefer using the computer techniques over the traditional methods for gathering and presenting information. 相似文献
13.
针对目前地基GNSS台站在全球分布不均匀,导致南半球海洋和中高纬地区出现与实际不符的VTEC为负值的问题,利用IGS前1 d的最终GIM作为虚拟观测值对TEC可能为负值的地区进行约束,结合GNSS数据建立全球电离层模型(称为SGG模型),并用2014年200多个IGS台站数据对模型进行验证。结果表明,各台站VTEC的RMS优于3 TECu(赤道异常区域RMS在5~7 TECu)。同时SGG能有效消除南半球海洋(40°~90°S)VTEC为负的情况,且对原有非负VTEC几乎没有影响(其变化小于2 TECu)。SGG的卫星DCB与CODE 相比,RMS和MEAN分别优于0.2 ns和0.04 ns,不同纬度带SGG与CODE的接收机DCB估值变化基本一致,两者之差基本在1 ns以内。 相似文献
14.
The effect of scattering in surface wave tomography 总被引:6,自引:1,他引:6
Jesper Spetzler Jeannot Trampert Roel Snieder 《Geophysical Journal International》2002,149(3):755-767
15.
Invasive species pose global biological and economic challenges. Over the past four decades, Prosopis taxa have emerged as a major invader of the arid and semi-arid regions of the world. Prosopis juliflora, one of the highly invasive Prosopis species, is dominantly present in the Afar region of Ethiopia and continues to spread into the surrounding areas. The objective of this study was to aid the mapping, utilization, and management of the invasive P. juliflora in Afar, by employing participatory research techniques. We assessed the introduction history, impacts, uses, and control strategies of invasive P. juliflora by interviewing 108 pastoralists and agro-pastoralists. In addition, we used Participatory Mapping (PM), Geographic Information Systems (GIS), Global Positioning System (GPS), and remote sensing technologies and approaches to map sites invaded by P. juliflora. Sketch maps were produced by men, women, pastoralist and agro-pastoralist groups. Experts aggregated, scaled and reproduced the sketch maps with support from the Afar communities. We provided GPS and GIS trainings to selected community members who assisted us in collecting the GPS locations of more than 70 key features and landmarks. The sketch maps were digitized and geo-referenced by experts using the 70 GPS records as control points. Geo-referenced community maps were superimposed on pan-sharpened Landsat 8 satellite images and presented to the communities for verification. We overlaid the verified community maps on ancillary land-cover layers, and detected the land-cover classes that were most affected by P. juliflora invasion. Despite its uses as source of fire wood, charcoal, and animal fodder, the species has adverse impacts on native species and livestock resources. Afar communities mapped P. juliflora infestations, particularly those that occurred near their villages, using high and moderate density classes. The two highly invaded land-cover categories were dense grassland, and exposed sand & soils. Participants collaborated in creating the produced maps, suggesting that participatory research approaches are another tool for early detection of invasive species and guiding fine-scale management strategies. 相似文献
16.
17.
The seismic history of the city of Ragusa (Italy), the geotechnical characterisation of the subsoil and the site response analysis should be correctly evaluated for the definition of the Seismic Geotechnical Hazard of the city of Ragusa, through geo-settled seismic microzoning maps. Basing on the seismic history of the city of Ragusa, the following earthquake scenarios have been considered: the “Val di Noto” earthquake of January 11, 1693 (with intensity X–XI on MCS scale, magnitude MW=7.41 and epicentral distance of about 53 km); the “Etna” earthquake of February 20, 1818 (with intensity IX on MCS scale, magnitude MW=6.23 and epicentral distance of about 64 km); the Vizzini earthquake of April 13, 1895 (with intensity I=VII–VIII on MCS scale, magnitude MW=5.86 and epicentral distance of about 26 km); the “Modica” earthquake of January 23, 1980 (with intensity I=V–VI on MCS scale, magnitude MW=4.58 and epicentral distance of about 10 km); the “Sicilian” earthquake of December 13, 1990 (with intensity I=VII on MCS scale, magnitude MW=5.64 and epicentral distance of about 50 km). Geotechnical characterisation has been performed by in situ and laboratory tests, with the definition of shear wave velocity profiles in the upper 30 m of soil. Soil response analyses have been evaluated for about 120 borings location by some non-linear 1-D models. Finally the seismic microzonation of the city of Ragusa has been obtained in terms of maps with different peak ground acceleration at the surface; shaking maps for the central area of the city of Ragusa were generated via GIS for the earthquake scenarios. 相似文献
18.
On the basis of maps of sea level anomalies data set from October 1992 to January 2004, pronounced low frequency variations with periods of about 500 d are detected in the area near 20°N from 160°W to 130°E. A linear two-layer model is employed to explain the mechanism. It is found that the first-mode long baroclinic Rossby waves at 20°N in the northwest Pacific propagate westward in the form of free waves at a speed of about 10.3 cm/s. This confirms that the observed low frequency variabilities appear as baroclinic Rossby waves. It further shows that these low frequency variabilities around 20°N in the northwest Pacific can potentially be predicted with a lead up to 900 d. 相似文献
19.
20.
The diagenetic transformation of biogenic silica from opal-A to opal-CT was recognised on seismic reflection data over an area of 78 × 103 km2 on the mid-Norwegian margin. The opal-A/CT diagenetic boundary appears as a positive, high amplitude reflection that generally cross-cuts the hosting stratigraphy. We demonstrate that it is not a sea bottom simulating reflection (BSR) and also that is not in thermal equilibrium with the present day isotherms. We present arguments that three styles of deformation associated with the opal-A/CT reflection – polygonal faulting, regional anticlines and synclines and differential compaction folding – indicate that the silica diagenesis reaction front is fossilised at a regional scale. Isochore maps demonstrate the degree of conformity between the opal-A/CT reflection and three seismic horizons of Late Miocene to Early Pliocene age that potentially represent the paleo-seabed when ‘fossilisation’ of the reaction front took place. The seismic interpretational criteria for recognition of a fossilised diagenetic front are evaluated and the results of our study are integrated with previous studies from other basins of the NE Atlantic in order to determine if the arrest of silica diagenesis was diachronous along this continental margin. 相似文献