Boundary condition control of fluvial obstacle mark formation – framework from a geoscientific perspective     

Oliver Schlömer  Jürgen Herget  Thomas Euler 《地球表面变化过程与地形》2020,45(1):189-206

Obstacle marks are sedimentary bedforms, typically composed of an upstream local scour hole and a downstream sediment accumulation in the vicinity of an obstruction that is exposed to a current. However, specific morphologies are variable in fluvial, coastal and submarine environments. Although obstacle marks and the phenomenon of local scouring are subject to different scientific disciplines, the objectives of investigations are rather incoherent and no systematic framework for analysing and evaluating boundary condition control exists yet, especially concerning limited knowledge of the cause and effect relationship of obstacle mark formation at instream boulders or vegetation elements in variable environmental conditions. Thus, a parameter framework is developed which identifies a spectrum of extrinsic and intrinsic boundary conditions that control the major process dynamics of obstacle mark formation. The framework is composed of dimensionless control parameters that are separated by a hierarchical order regarding their significance for obstacle mark formation. Primary control parameters determine the geometrical scale of flow field at the obstacle, and therefore control the potential maximum size of the obstacle. Secondary control parameters affect the dynamics of the flow field in geometrical scale and limit the potential maximum size of the emerging sedimentary structure if thresholds are crossed. The framework is supposed to be a foundation for subsequent quantification and determination of thresholds by systematic laboratory studies. To elucidate this, flume-based research is presented, evaluating the influence of different flow levels at boulder-like obstacles of different shapes. The results show that obstacle mark dimensions were maximized at shallow flow depths compared to obstacle dimensions, while deep flows at submerged boulder-like obstructions caused considerably smaller obstacle marks. In interdependency with a rounded and more streamlined obstacle shape, deep flows even cause a deviation of morphology if the flow depth above an obstacle exceeds 1.6 times the obstacle's dimensions. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

云南元阳—马关地区布格重力异常及其找矿意义     

黄元有  冉灿  吕许朋 《云南地质》2011,30(3):336-339,331

评细研究区布格重力局部异常后认为:元阳哈播为金、铜、铅锌找矿有利地段,金平-新安里为金、铅锌、铜、钼多金属找矿地段,个旧老厂为锡多金属矿成矿有利部位,薄竹山为钨、银铅锌找矿区,而马关老君山为钨、铜、铅锌多金属矿有利地段。  相似文献   

Review Paper: Historical development of the total normalized gradient method in profile gravity field interpretation     

I.S. Elysseieva  R. Pašteka 《Geophysical Prospecting》2019,67(1):188-209

In the Russian school, the total normalized gradient method belongs to the most wide-spread of direct interpretation methods for potential field data. This method was also used and partly developed by many experts from abroad. The main advantage of the total normalized gradient method is its relative independence of parameters such as the expected differential density of interpreted structures. The method is built from a construction of a specially transformed field (total normalized gradient) on a section crossing the potential field sources. The special properties of this transformed field allow it to be used to detect the source positions. From the 1960s, the mathematical basis of the method underwent enormous development and several modifications of the method have been elaborated. The total normalized gradient operator itself represents a relatively complicated, non-linear band-pass filter in the spectral domain. The properties of this operator can be handled by means of several parameters that act to separate the information about field sources at different depth levels. In this contribution, we describe the development of the method from its very beginning (based mostly on qualitative interpretation of simple total normalized gradient sections) through to more recent numerical improvements to the method. These improvements include the quasi-singular points method, which refines the filter properties of the total normalized gradient operator and defines an objective criteria (so called criterion ‘α’ and ‘Г') for the definition of source depths in the section. We end by describing possibilities for further development of the method in the future.  相似文献   

Maximizing the information return from ground penetrating radar     

Gary R. Olhoeft 《Journal of Applied Geophysics》2000,43(2-4)

Ground penetrating radar data is not always easy to acquire, and sometimes the acquisition may be constrained by equipment availability, weather, legal or logistical constraints, safety or access considerations. Examples of these include archaeological or geotechnical sites about to be excavated, contaminated lands undergoing remediation, hazardous areas such as unexploded ordnance lands or active volcanoes, and difficult to visit locations such as Antarctica or the surface of Mars. These situations may result in only one chance at acquiring data. Thus, the data need to be acquired, processed and modeled with the aim of maximizing the information return for the time, cost and hazard risked. This process begins by properly setting up the survey with the expectation of the site conditions but allowing for flexibility and serendipity in the unknown. Not only are radar data acquired, but also calibration, orientation, location and other required parameters describing the equipment and survey are recorded. All of these parameters are used in the processing and modeling of the data. The final results will be not just a radar image as a pseudo-cross-section, but a corrected geometric cross-section, interpreted electrical and magnetic properties of the ground, location, orientation, size and shape of subsurface objects, and composition of the ground and objects as inferred density, porosity, fluid saturation, and other relevant material occurrence properties.  相似文献   

Increasing illumination and sensitivity of reverse‐time migration with internal multiples     

Clement Fleury 《Geophysical Prospecting》2013,61(5):891-906

Reverse‐time migration is a two‐way time‐domain finite‐frequency technique that accurately handles the propagation of complex scattered waves and produces a band‐limited representation of the subsurface structure that is conventionally assumed to be linear in the contrasts in model parameters. Because of this underlying linear single‐scattering assumption, most implementations of this method do not satisfy the energy conservation principle and do not optimally use illumination and model sensitivity of multiply scattered waves. Migrating multiply scattered waves requires preserving the non‐linear relation between the image and perturbation of model parameters. I modify the extrapolation of source and receiver wavefields to more accurately handle multiply scattered waves. I extend the concept of the imaging condition in order to map into the subsurface structurally coherent seismic events that correspond to the interaction of both singly and multiply scattered waves. This results in an imaging process referred to here as non‐linear reverse‐time migration. It includes a strategy that analyses separated contributions of singly and multiply scattered waves to a final non‐linear image. The goal is to provide a tool suitable for seismic interpretation and potentially migration velocity analysis that benefits from increased illumination and sensitivity from multiply scattered seismic waves. It is noteworthy that this method can migrate internal multiples, a clear advantage for imaging challenging complex subsurface features, e.g., in salt and basalt environments. The results of synthetic seismic imaging experiments, including a subsalt imaging example, illustrate the technique.  相似文献   

Diffraction imaging of sub‐vertical fractures and karst with full‐resolution 3D Ground‐Penetrating Radar     

Mark Grasmueck  Miquel Coll Quintà  Kenri Pomar  Gregor P. Eberli 《Geophysical Prospecting》2013,61(5):907-918

Vertical fractures with openings of less than one centimetre and irregular karst cause abundant diffractions in Ground‐Penetrating Radar (GPR) records. GPR data acquired with half‐wavelength trace spacing are uninterpretable as they are dominated by spatially undersampled scattered energy. To evaluate the potential of high‐density 3D GPR diffraction imaging a 200 MHz survey with less than a quarter wavelength grid spacing (0.05 m × 0.1 m) was acquired at a fractured and karstified limestone quarry near the village of Cassis in Southern France. After 3D migration processing, diffraction apices line up in sub‐vertical fracture planes and cluster in locations of karstic dissolution features. The majority of karst is developed at intersections of two or more fractures and is limited in depth by a stratigraphic boundary. Such high‐resolution 3D GPR imaging offers an unprecedented internal view of a complex fractured carbonate reservoir model analogue. As seismic and GPR wave kinematics are similar, improvements in the imaging of steep fractures and irregular voids at the resolution limit can also be expected from high‐density seismic diffraction imaging.  相似文献   

基于ZY-102C星数据的遥感地质解译——以塔吉克斯坦帕米尔地区为例   总被引：1，自引：0，他引：1  

张焜  李宗仁  马世斌 《国土资源遥感》2015,(3)

为了对境外地质矿产勘查开发提供遥感信息支持,在综合前人研究成果及野外验证基础上,对塔吉克斯坦帕米尔地区的地质和构造特征进行深入分析和研究;根据不同地质体的特征影像,对照"资源一号"(ZY-1)02C星遥感图像中所显示的地貌景观、色调及纹形等,建立了塔吉克斯坦南部地区主要沉积岩、变质岩和侵入岩以及断裂构造、褶皱构造和环形构造等的遥感解译标志;通过对ZY-1 02C星的全色/多光谱相机(P/MS)和全色高分辨率相机(HR)数据的遥感地质解译效果对比,认为P/MS数据中地质体的色调差异更为明显,易于建立区域构造格架、开展岩石大类解译;而HR数据所反映地质体的微地貌、纹理及细节更为清晰,易于进一步识别各类岩性及小型构造,尤其对碎屑岩的粒度、层状构造类型、第四系、矿业活动以及特殊成分的岩石等具有较好的反映。  相似文献   

延川县地质灾害详细调查实践与认识     

侯喜燕  张锦  张秦华  许冰权 《陕西地质》2010,28(1):92-97

延川县地处陕北黄土梁峁沟壑区,地质灾害频发。通过遥感解译、地面调查,查明了区内地质灾害类型、规模、特点及其分布规律。  相似文献   

Perspectives on Quaternary outreach and aspirations for the future     

David E. Anderson  Eleanor J. Brown 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(4):455-467

Outreach arising from the study of the British Quaternary offers many benefits for society, especially because of its relevance for understanding contemporary environmental issues and environmental change. Outreach is also important for the long-term health of the academic discipline and research agenda. Through engaging with the formal education system, institutions, policy makers, planners and with the public at large, Quaternary specialists can do much to advance interest in and appreciation of the British landscape and its Quaternary record. This opinion and review article considers the importance and benefits of outreach in its many forms, makes the case for practitioners to continue and increase their involvement, offers examples of good practice, and sets out aspirations for the future.  相似文献   

基于三维的地质灾害遥感解译标志管理系统设计与实现   总被引：1，自引：0，他引：1  

乌云其其格  马维峰  张时忠  唐湘丹  刘文婷 《国土资源遥感》2012,(2):148-151

总结了滑坡、泥石流地质灾害解译标志的内容和特点,建立了解译标志的数据模型和数据库,并对地质灾害的解译标志信息进行编码,研制了基于Virtual Globe三维环境的地质灾害解译标志管理系统.该系统对有效存储管理地质灾害解译标志,提高地质灾害遥感解译的工作效率具有重要价值.  相似文献