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1.
SHIKHAR C. JAIN 《Geophysical Prospecting》1974,22(3):445-457
Theoretical broadside resistivity profiles over an outcropping dyke of infinite depth extent with three Wenner configurations (namely Alpha, Beta and Gamma), Schlumberger, and two-electrode configurations of various electrode spacings and for various reflection factors are presented. The broadside profiles qualitatively indicate that the shape of the anomaly is invariant with the electrode configurations. The various electrode configurations can be arranged in decreasing order of magnitude of anomalies as Beta Wenner, Alpha Wenner, Schlumberger, Gamma Wenner, and two-electrode. The broadside Wenner profiles also show larger anomalies compared to those in inline profiles. 相似文献
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Combined open channel flow is encountered in many hydraulic engineering structures and processes, such as irrigation ditches and wastewater treatment facilities. Extensive experimental studies have conducted to investigate combined flow characteristics. Nevertheless, there is no simple relationship that can fully describe the velocity profiles in a turbulent flow. The artificial neural network (ANN) has great computational capability for solving various complex problems, such as function approximation. The main objective of this study is to evaluate the applicability of the ANN for simulating velocity profiles, velocity contours and estimating the discharges accordingly. The velocity profiles measured by an acoustic doppler velocimeter in the open channel of the Chihtan purification plant, Taipei, with different discharges at fixed measuring section and different depths are presented. The total number of data sets is 640 and the data sets are split into two subsets, i.e. training and validation sets. The backpropagation algorithm is used to construct the neural network. The results demonstrate that the velocity profiles can be modelled by the ANN, and the ANN constructed can nicely fit the velocity profiles and can precisely predict the discharges for the conditions investigated. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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M. R. de Quervain 《水文科学杂志》2013,58(4):21-25
Abstract This study of longitudinal stream profiles of rivers of the Midcontinent (rivers tributary to the Mississippi) and Atlantic and East Gulf Slopes has revealed five types of longitudinal profiles: (1) Overall concave-upward profiles with or without long constant slope segments; (2) convex upward, for example, the Missouri River has a profile that has a constant slope for its lower 560 miles and then is convex upward with constant slope segments to a point beyond the Yellowstone River junction; (3) concave-upward irregular, ungraded, low-gradient profiles (Ohio and Tennessee Rivers); (4) irregular unsegmented and steep profiles, such as shown by the Delaware and Savannah-Tugaloo Rivers; and (5) irregular ungraded, steep-gradient profiles that are concave-upward in the upstream reaches and downstream convex-upward, for example, on most of the Atlantic Slope and East Gulf Slope Rivers above the Fall Line. Constant slope profiles occur where the last type of rivers flow across relatively weak Coastal Plain sediments and also inland on the Coosa and Oostanaula-Conasauga Rivers. The profile characteristics of the Atlantic and East Gulf streams lend support to the hypothesis of multiple erosion cycles in the Appalachians. 相似文献
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A detailed study of the morphology and micro‐morphology of Quaternary alluvial calcrete profiles from the Sorbas Basin shows that calcretes may be morphologically simple or complex. The ‘simple’ profiles reflect pedogenesis occurring after alluvial terrace formation and consist of a single pedogenic horizon near the land surface. The ‘complex’ profiles reflect the occurrence of multiple calcrete events during terrace sediment aggradation and further periods of pedogenesis after terrace formation. These ‘complex’ calcrete profiles are consequently described as composite profiles. The exact morphology of the composite profiles depends upon: (1) the number of calcrete‐forming events occurring during terrace sediment aggradation; (2) the amount of sediment accretion that occurs between each period of calcrete formation; and (3) the degree of pedogenesis after terrace formation. Simple calcrete profiles are most useful in establishing landform chronologies because they represent a single phase of pedogenesis after terrace formation. Composite profiles are more problematic. Pedogenic calcretes that form within them may inherit carbonate from calcrete horizons occurring lower down in the terrace sediments. In addition erosion may lead to the exhumation of older calcretes within the terrace sediment. Calcrete ‘inheritance’ may make pedogenic horizons appear more mature than they actually are and produce horizons containing carbonate embracing a range of ages. Calcrete exhumation exposes calcrete horizons whose morphology and radiometric ages are wholly unrelated to terrace surface age. Composite profiles are, therefore, only suitable for chronological studies if the pedogenic horizon capping the terrace sequence can be clearly distinguished from earlier calcrete‐forming events. Thus, a detailed morphological/micro‐morphological study is required before any chronological study is undertaken. This is the only way to establish whether particular calcrete profiles are suitable for dating purposes. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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The finite element method, here viewed as a special case of the Galerkin projective method, is applied to the modelling of magnetotelluric problems, and its adaptation to geological profiles is outlined. A novel method for obtaining surface field values, involving matrix representation of the normal derivative operator, is presented in detail. Results obtained by this method are compared with well-known infinite series solutions for the vertical fault and the outcropping dyke. Two profiles containing sulphide zones are also modelled, the results being compared with field data; satisfactory agreement is obtained. 相似文献
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分别在湖北省药姑山和九宫山的山头上开展GPS掩星观测实验，成功获取山基掩星观测数据，对掩星事件进行了分析和统计.给出利用山基掩星观测数据反演大气折射指数剖面和电波弯曲角的原理和算法.利用山基GPS掩星观测模拟数据，对反演方法进行试算和检验，结果表明反演方法准确可行.将该反演方法应用于观测数据的反演，获得了观测点高度以下的大气折射率剖面，以及电波弯曲角.实验结果和原理研究表明，山基掩星观测技术是一种潜在的低层大气环境监测新技术. 相似文献
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The time-average velocity profiles of the flows carrying natural sand particles and three kinds of plastic particles as suspension and neutrally buoyant load are measured and analyzed. The velocity profiles of the sediment-laden flow can approximately be divided into two regions - the near-bed region and the far-bed region. Main factors affecting the velocity profiles are viscosity, density gradient, grain shear stress and damping of turbulence due to particles. Based on these physical conceptions, a velocity profile model of sediment-laden flow is developed. It agrees well with the experimental data. The discrepancy is 1.57% for the plastic particle-laden flow and 3.67% for the natural sand-laden flow. In the far-bed region, von Karman constants are smaller than those of the clear water flow. 相似文献
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为开展秦岭翠华山等大型花岗岩地震山崩的动力响应机制研究,研发配制用于振动台物理模型试验的花岗岩相似材料是该研究工作的基础。选取铁矿粉、石英砂、重晶石粉为骨料,石膏为调节材料,松香酒精溶液为黏结剂的相似材料配比方案,设计考虑4因素5水平的正交试验,并对试验结果进行极差分析及多元线性回归拟合,获得各因素对花岗岩相似材料物理力学性质的影响结果和相似材料配比经验方程。结果表明：花岗岩相似材料的密度随铁粉与重晶石粉占骨料比的增加而增大;随着黏结剂浓度的增加,花岗岩相似材料的抗压强度、弹性模量及黏聚力均显著增大;随着石膏含量的增加,密度、抗压强度及内摩擦角均减小。该试验得到的相似材料配比经验方程可以较好地为花岗岩相似材料或其他相似材料的配制提供参考。 相似文献
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Christopher Juhlin Hans Palm Carl-Fredrik Müllern Bo Wllberg 《Journal of Applied Geophysics》2002,51(2-4)
Two high-resolution reflection seismic profiles were acquired in the Heby area of eastern Sweden over glacial deposits for the purpose of mapping groundwater resources. The majority of shot points were located in clay resulting in good quality data along most of the profiles. On stacked and migrated sections, the uppermost clay is about 20 m thick and is characterized by its subhorizontal reflectivity. Sand/gravel deposits below it contain more dipping interfaces and have a chaotic reflectivity pattern. Depth to bedrock is interpreted to be 90 and 65 m on the respective profiles and occurs in about a 100-m-wide trough on both profiles. Reflections from the tops of sandy gravel zones generally have higher amplitudes. Clear reflections from a thin silt layer (20 cm thick) at about 10-m depth are observed on one of the profiles. Elastic finite difference modeling and the observation of this reflection in shot gathers show that the reflection is not an artifact of the acquisition nor the processing. The modeling also shows that there is no marked low-velocity waveguide in the near surface, but that an effective low Q zone may be present. Comparison with refraction profiling on the other profile shows that there is better agreement between the reflection seismic results and penetration tests than the refraction results with these tests. Both profiles allow the thickness of the overlying clay layers to be determined, as well as the thickness of the underlying sand/gravel deposits. This is important for estimating the amount of groundwater resources in an area. 相似文献
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We propose a new quantitative determination of shear wave velocities for distinct geological units in the Bohemian Massif,
Czech Republic (Central Europe). The phase velocities of fundamental Love wave modes are measured along two long profiles
(~200 km) crossing three major geological units and one rift-like structure of the studied region. We have developed a modified
version of the classical multiple filtering technique for the frequency-time analysis and we apply it to two-station phase
velocity estimation. Tests of both the analysis and inversion are provided. Seismograms of three Aegean Sea earthquakes are
analyzed. One of the two profiles is further divided into four shorter sub-profiles. The long profiles yield smooth dispersion
curves; while the curves of the sub-profiles have complicated shapes. Dispersion curve undulations are interpreted as period-dependent
apparent velocity anomalies caused both by different backazimuths of surface wave propagation and by surface wave mode coupling.
An appropriate backazimuth of propagation is found for each period, and the dispersion curves are corrected for this true
propagation direction. Both the curves for the long and short profiles are inverted for a 1D shear wave velocity model of
the crust. Subsurface shear wave velocities are found to be around 2.9 km/s for all four studied sub-profiles. Two of the
profiles crossing the older Moldanubian and Teplá-Barrandian units are characterized by higher velocities of 3.8 km/s in the
upper crust while for the Saxothuringian unit we find the velocity slightly lower, around 3.6 km/s at the same depths. We
obtain an indication of a shear wave low velocity zone above Moho in the Moldanubian and Teplá-Barrandian units. The area
of the Eger Rift (Teplá-Barrandian–Saxothuringian unit contact) is significantly different from all other three units. Low
upper crust velocities suggest sedimentary and volcanic filling of the rift as well as fluid activity causing the earthquake
swarms. Higher velocities in the lower crust together with weak or even missing Moho implies the upper mantle updoming. 相似文献
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This paper discusses variability and accuracy of site response predictions performed using shear wave velocity (Vs) profiles derived from non-unique surface wave inversions and other commonly used statistical methods of accounting for epistemic uncertainty and aleatory variability in Vs. Specifically, linear and equivalent linear site response analyses were performed on the following three classes of Vs profiles: (1) 350 Vs profiles developed by performing multiple surface wave inversions, each with a unique set of layering parameters, on a common dispersion dataset, (2) two upper/lower range base-case Vs profiles developed by systematically increasing or decreasing the solution Vs profile by 20%, and (3) 100 Vs profiles developed using the Vs randomization procedure proposed by Toro (1995) [26]. Vs profiles derived from surface wave inversions generally yielded accurate site response estimates with minimal variability, so long as their theoretical dispersion data fit the experimental dispersion data well. On the other hand, the upper/lower range and randomized Vs profiles generally produced inaccurate and highly variable site response predictions, although the inclusion of site-specific parameters in the randomization model improved the results. At real sites where substantial aleatory variability is anticipated and/or the epistemic uncertainty is quite high, the site response estimates associated with the randomized and/or upper/lower range Vs profiles may be deemed acceptable. However, if the experimental dispersion data and horizontal-to-vertical spectral ratios are shown to be consistent over the footprint of a site, it may be possible to significantly reduce the uncertainty associated with the input Vs profile and the resulting uncertainty in the site response. 相似文献
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TOMOKI TSUTSUI 《Geophysical Prospecting》1992,40(1):15-30
A method for pseudoreflection profiling (PRP) is presented. By using transmission seismograms, this method produces time sections similar to those obtained using the common depth point (CDP) method. Pseudoreflection profiles are obtained using the following procedure. Equivalent transmission responses at sites on soft deposits are derived by Wiener filter estimation using seismograms acquired on the sites and on the basement rock. These responses are substituted into the Claerbout-Kunetz equation to obtain the pseudoreflection profiles. A 3D subsurface model is produced when the PRP method is applied to explosion seismograms. The time sections thus obtained are consistent with those obtained using the CDP method in a neighbouring area. The maximum station interval for obtaining coherent profiles with this method is estimated to be one quarter of the wavelength of the transmitted waves. This technique should be used in combination with another method such as the CDP method because it has two weak points: the velocity structure cannot be obtained directly and undesirable waves cannot be eliminated through processing. 相似文献
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《Journal of Atmospheric and Solar》2008,70(10):1281-1288
Simultaneous and complete temperature profiles from near ground to about 100 km are essential for studying the dynamical coupling between different atmospheric layers. They are acquired by combining three different lidar techniques at Wuhan, China (30.5°N, 114.4°E). The atmospheric temperatures from about 3 to 25 km are calculated from the nitrogen molecule density profiles obtained from the N2 vibrational Raman backscatter, while the atmospheric temperatures between 30 and ∼75 km are calculated by the standard Rayleigh scattering method. The temperatures in the 80–100 km altitude region are derived from the Fe Boltzmann technique. The temperature profiles measured by our lidar systems exhibit good agreement when compared with the radiosonde and satellite data, as well as the model. A Lomb–Scargle spectral analysis of the normalized temperature perturbations in the altitude range from 4 to 60 km shows that the spectral slopes of the vertical wave number spectra tended to −3 for large vertical wave numbers. This is consistent with the model predictions of saturated gravity wave spectra. 相似文献
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Ivana Nemešová 《Studia Geophysica et Geodaetica》1991,35(3):244-249
Summary The paper deals with the role of penetrative downdrafts in the convective adjustment suggested by Betts[1]. Three different types of downdraft sinking levels are used in the assessment of the reference profiles of temperature and humidity in cumulus cloud layers and these are compared with the profiles with no downdraft. It is shown that the depths of downdraft penetration may significantly influence the reference profiles mainly for clouds of vertical extents larger than one kilometre. 相似文献
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We study erosion depth and sediment fluxes for wave-induced sheet-flow, and their dependency on grain size and streaming. Hereto, we adopt a continuous two-phase model, applied before to simulate sheet-flow of medium and coarse sized sand. To make the model applicable to a wider range of sizes including fine sand, it appears necessary to adapt the turbulence closure of the model. With an adapted formulation for grain–carrier flow turbulence interaction, good reproductions of measured erosion depth of fine, medium and coarse sized sand beds are obtained. Also concentration and velocity profiles at various phases of the wave are reproduced well by the model. Comparison of sediment flux profiles from simulations for horizontally uniform oscillatory flow as in flow tunnels and for horizontally non-uniform flow as under free surface waves, shows that especially for fine sand onshore fluxes inside the sheet-flow layer increase under influence of progressive wave effects. This includes both the current-related and the wave-related contribution to the period-averaged sheet-flow sediment flux. The simulation results are consistent with trends for fine and medium sized sediment flux profiles observed from tunnel and flume experiments. This study shows that the present two-phase model is a valuable instrument for further study and parameterization of sheet-flow layer processes. 相似文献
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地球内部物理学和地球动力学在地球科学研究领域里占有重要地位.为了研究和探索我国大陆不同大地构造单元和板内特异块体与其界带的深部介质属性、结构和深层物理-力学过程,已在我国最先构思、设计、布署并实施了十条人工源深部地震探测剖面.沿这十条第一剖面进行了高精度的地震反射、宽角反射和折射波场观测,进行了数据采集,获得了深部高分辨率的信息.通过数据处理和反演求得了各剖面辖区的沉积建造、结晶基底、地壳与土地幔的差异和层、块精细速度结构,发现、研究和提出了一系列的重要科学问题并取得了一系列新认识.为研究成山、成盆、成岩、成矿、成灾,圈层耦合和深化认识地球本体与动力学响应打下了坚实的基础,明确指出了其深入研究的内涵和发展导向. 相似文献
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Evaluating proxies for estimating subaerial beach volume change across increasing time scales and various morphologies 
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下载免费PDF全文 Proxies, such as changes in beach profiles and shoreline positions, are commonly used in management and research for estimating changes in subaerial beach volume; however, the accuracy of these proxies across increasing time scales and complex morphologies is unclear. Volume changes associated with along‐beach morphologic variability may not be captured well by changes in profiles, while volume changes associated with across‐beach morphologic variability may not be captured well by measuring shoreline change. This study assesses the impacts of morphologic variations, associated with beach cusps and nourishment material, on volume change estimates from profiles and shoreline change at 0.5 to 3.5 year time periods. Results indicate that profiles spaced ≥ 150 m apart and the shoreline‐change proxy will likely estimate volume change inaccurately over periods ≤ 1 year at beaches that are consistently eroding or accreting and contain cusps. However, over longer time periods (1–3.5 years), estimates of volume change from both proxies improved at those types of beaches. Volume changes at the edges of nourishment areas are not captured well by profiles. When the nourishment material is graded to a ramped morphology, which minimizes across‐beach morphologic variability, the shoreline‐change proxy does accurately estimate volume changes. Both proxies estimate volume changes inaccurately at beaches where volume changes oscillate between erosion and accretion on both short and long time scales because the magnitude of small‐scale changes in volume from the formation and erosion of morphologic features, such as cusps and berms, will always be similar to the longer‐term net volume change. This study suggests that decadal records of shoreline change, which are commonly developed using aerial photography, can be used to help identify the best proxy for estimating volume change; however, recent anthropogenic modifications that impact patterns of beach sedimentation, including nourishment, terminal groins, and inlet‐channel dredging, makes decadal records less useful. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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The surface resistivity method has been used to study a few exposed coal seams located in the northwestern part of the Raniganj Coalfield (belonging to the Damodar Valley Gondwana basin), India. Different electrode configurations, viz., Wenner, two-electrode and half-Schlumberger, have been used with different electrode spacings in horizontal profiling. The vertical distribution of resistivity has been studied using Schlumberger configuration at different locations along the profile. Laboratory studies of resistivity (at partial to full water saturation conditions) and porosity of different coal, shaly sandstone and sandstone samples of the survey area had already been carried out before the field survey. The results indicated the presence of a good resistivity contrast between the coal seams and the surrounding formations. The field results did not bear this out: the resistivity responses of the coal formations on the profiles and sounding curves are not as clear as one would expect for such high contents. The Wenner profiles show a broad resistivity anomaly over the coal seams. Two-electrode profiles are less noisy than Wenner profiles. Sharp peaks have been observed over the coal seams. The half-Schlumberger configuration seems the best: all the coal seams and their edges can be accurately outlined on the resistivity curves. Borehole data close to the profile have been used for correlating the field results. There is good agreement with vertical electrical soundings. 相似文献