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1.
The microstructure charateristics of illite from the Chuanlinggou Formation of Changcheng System (Chch) in Jixian County, Tianjin City has been studied by means of high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), X-ray energy dispersive spectrum (EDS) and X-ray powder diffraction (XRD). The Kübler index of "illite crystallinity" is 0.505°△2θ, which indicates that the host rock is in a middle diagenetic stage. The chemical analyses of EDS for illite studied indicate a heavily absent in interlayer cation and an average chemical formula of K0.57(Al1.80Mg0.42Fe2 0.12)Σ=2.34 (Si2.92Al1.08)Σ=4O10(OH)2. It is found, from one-dimensional lattice images, that the layers of illite not only stack in a flat way but also in a curving way. A "matting fabric" illite structure results from stacking faults. Combined with SAED analysis the illite studied can be affirmed as 1M illite. The two-dimensional lattice images are obtained from [100] and [110] incidences, whose lattice images have the same d-values but different intersecting angles. The two-dimensional lattice image with [100] incidence is orthogonal to each other, whilst that with [110] incidence is oblique. This paper provides some important structure information of authigenic clay minerals for the well-known mesoproterozoic section of Jixian County.  相似文献   

2.
Wavefield‐based migration velocity analysis using the semblance principle requires computation of images in an extended space in which we can evaluate the imaging consistency as a function of overlapping experiments. Usual industry practice is to assemble those seismic images in common‐image gathers that represent reflectivity as a function of depth and extensions, e.g., reflection angles. We introduce extended common‐image point (CIP) gathers constructed only as a function of the space‐ and time‐lag extensions at sparse and irregularly distributed points in the image. Semblance analysis using CIP's constructed by this procedure is advantageous because we do not need to compute gathers at regular surface locations and we do not need to compute extensions at all depth levels. The CIP's also give us the flexibility to distribute them in the image at irregular locations aligned with the geologic structure. Furthermore, the CIP's remove the depth bias of common‐image gathers constructed as a function of the depth axis. An interpretation of the CIP's using the scattering theory shows that they are scattered wavefields associated with sources and receivers inside the subsurface. Thus, when the surface wavefields are correctly reconstructed, the extended CIP's are characterized by focused energy at the origin of the space‐ and time‐lag axes. Otherwise, the energy defocuses from the origin of the lag axes proportionally with the cumulative velocity error in the overburden. This information can be used for wavefield‐based tomographic updates of the velocity model, and if the velocity used for imaging is correct, the coordinate‐independent CIP's can be a decomposed as a function of the angles of incidence.  相似文献   

3.
The microstructure charateristics of illite from the Chuanlinggou Formation of Changcheng System (Chch) in Jixian County, Tianjin City has been studied by means of high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), X-ray energy dispersive spectrum (EDS) and X-ray powder diffraction (XRD). The Kübler index of "illite crystallinity" is 0.505°△2θ, which indicates that the host rock is in a middle diagenetic stage. The chemical analyses of EDS for illite studied indicate a heavily absent in interlayer cation and an average chemical formula of K0.57(Al1.80Mg0.42Fe2 0.12)∑=2.34 (Si2.92Al1.08)∑=4O10(OH)2. It is found, from one-dimensional lattice images, that the layers of illite not only stack in a flat way but also in a curving way. A "matting fabric" illite structure results from stacking faults. Combined with SAED analysis the illite studied can be affirmed as 1M illite. The two-dimensional lattice images are obtained from [100] and [110] incidences, whose lattice images have the same d-values but different intersecting angles. The two-dimensional lattice image with [100] incidence is orthogonal to each other, whilst that with [110] incidence is oblique. This paper provides some important structure information of authigenic clay minerals for the well-known mesoproterozoic section of Jixian County.  相似文献   

4.
A local plane-wave approach of generalized diffraction tomography in heterogeneous backgrounds, equivalent to Kirchhoff summation techniques when applied in seismic reflection, is re-programmed to act as repeated synthetic aperture radar (SAR) imaging for seismic prestack depth migration. Spotlight-mode SAR imaging quickly provides good images of the electromagnetic reflectivity of the ground via fast Fourier transform (FFT)-based signal processing. By calculating only the Green's functions connecting the aircraft to the centre of the illuminated patch, scattering structures around that centre are also recovered. SAR technology requires us to examine seismic imaging from the local point of view, where the quantity and quality of the available information at each image point are what are important, regardless of the survey geometry. When adapted to seismics, a local image of arbitrary size and sampling is obtained by FFT of seismic energy maps in the scattering wavenumber domain around each node of a pre-calculated grid of Green's functions. These local images can be used to generate a classic prestack depth-migrated section by collecting only their centres. However, the local images also provide valuable information around the centre, as in SAR. They can therefore help to pre-analyse prestack depth migration efficiently, and to perform velocity analysis at a very low cost. The FFT-based signal-processing approach allows local, efficient and automatic control of anti-aliasing, noise and resolution, including optimized Jacobian weights. Repeated local imaging could also be used to speed up migration, with interpolation between local images associated with a coarse grid of Green's functions, as an alternative to interpolation of Green's functions. The local images may, however, show distortions due to the local plane-wave approximation, and the velocity variations across their frame. Such effects, which are not necessarily a problem in SAR, should be controlled and corrected to further enhance seismic imaging. Applications to realistic models and to real data show that, despite the distortion effects, the local images can yield similar information to prestack depth migration, including common-image-point gathers for velocity analyses and AVO/AVA effects, at a much lower cost when a small target is considered.  相似文献   

5.
The chemical composition of sediment sampled from a network of ice boreholes contacting the bed of the ablation zone of the Greenland Ice Sheet is compared to the composition of intact bedrock clasts. This sediment is enriched in silica and depleted in reactive cations compared to the underlying bedrock. In order to test whether these differences result from grain size biases either in sample collection or due to natural sorting, sediment samples were analyzed by grain size aliquots. Enrichment of silicon and depletion of cations is consistent across grain size classes and the compositions of bedrock and subglacial sediment are statistically separate. The difference in composition between subglacial sediment and rock aligns closely with the composition of dissolved solutes in waters sampled from the same field sites and is dissimilar to the composition of the sites' suspended sediment. This implies that chemical weathering rather than disproportionate physical removal of friable minerals is responsible for the compositional differences between rock and sediment. Mass balance analysis implies 3–10% of the sediment's mass is lost to solute dissolution, with approximately double that amount precipitated as clay minerals (a large portion of which may have been physically expelled). This result implies that temperate ice sheet subglacial environments may be more chemically active than previously realized. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

6.
Water quality in lakes is influenced by a large number of watershed and lake characteristics. In this study, we examined the relative effects of watershed land use and lake morphology on the trophic state of 19 lakes in the Yunnan plateau and lower Yangtze floodplain, the two most eutrophic regions in China. Trophic state parameters consisted of total nitrogen, total phosphorus, chemical oxygen demand, chlorophyll‐a, Secchi depth, and trophic state index, while lake morphometric variables included area, maximum depth, mean depth, water residence time (WRT), volume, and length to width ratio. Percentages of forest, grassland, cropland, unused land, built‐up land, and water body in each lake's watershed were extracted from a land use map interpreted from Landsat TM images. A t‐test indicated that lower Yangtze floodplain lakes were shallower and had higher percentages of cropland and built‐up land in watersheds than Yunnan plateau lakes. Pearson's correlation analysis indicated that both watershed land use and lake morphometric variables were significantly related to most of the trophic state parameters. However, stepwise regression analyses demonstrated that the trophic state of the lower Yangtze floodplain lakes was mainly controlled by the percentages of cropland and built‐up land in watersheds, while that of Yunnan plateau lakes was mostly determined by the lake depth and WRT. These results suggest that the relative effects of watershed land use and lake morphology on lake trophic state are dependent on the lake's location. This study can provide some useful information in watershed land use management for controlling eutrophication in Chinese lakes.  相似文献   

7.
The magnetic and gravity field produced by a given homogeneous source are related through Poisson's equation. Starting from this consideration, it is shown that some 2D interpretation tools, widely applied in the analysis of aeromagnetic data, can also be used for the interpretation of gravity gradiometric data (vertical gradient). This paper deals specifically with the Werner deconvolution, analytic signal and Euler's equation methods. After a short outline of the mathematical development, synthesized examples have been used to discuss the efficiency and limits of these interpretation methods. These tools could be applied directly to airborne gravity gradiometric data as well as ground gravity surveys after transformation of the Bouguer anomalies into vertical gradient anomalies. An example is given of the application of the Werner deconvolution and Euler's equation methods to a microgravity survey.  相似文献   

8.
水体富营养化引起的蓝藻水华问题,是我国湖泊面临的主要环境问题,亟需加强现状监测和变化研究;我国自主研发的环境(HJ)卫星空间分辨率高,重访周期短,可用于长时间序列蓝藻水华的动态监测.本文利用HJ卫星CCD数据,通过自动控制散点回归的方法进行相对辐射校正,再将归一化植被指数和像元生长算法相结合,提出了一种可业务化运行的蓝藻水华高精度提取算法.该算法的优点为:(1)水华提取时具有统一的阈值,解决了以往一景影像一个阈值,无法大规模批处理的难题;(2)通过对像元进行线性分解,精度可达到亚像元级别.利用该算法对太湖2009—2014年蓝藻水华进行监测,发现2013—2014年太湖蓝藻水华较以往暴发面积偏小.研究表明,该算法对蓝藻水华识别能力强,自动化程度和水华提取精度高,可作为业务化算法运行.  相似文献   

9.
We evaluate the potential of imaging for the first time, the near-earth space plasma environment seamlessly from the ionosphere through the magnetosphere by remotely sensing Thomson scattering of solar visible light by geospace electrons. Using state of the art first principles models of the magnetosphere/ionosphere system, we show that the column emission rates are weak, generally less than 10 Rayleighs, but detectable with currently available instrument technology recently deployed for heliospheric imaging. We demonstrate that distinct features such as the bow shock, magnetosheath and magnetopause are detectable in synthetic images simulated using modified solar coronagraphs and white light imagers, providing that the large background signals are properly quantified. The availability of global geospace images of the electron concentration will enable major advances in our understanding of how Earth's near-space environment responds as a coupled system to changing solar forcings. Such images are expected to play a central role in space weather assessment and forecasting, from which significant capabilities will accrue, much as the imaging of the Earth's surface and lower atmosphere has advanced understanding and forecasting of tropospheric weather.  相似文献   

10.
The Yellow River(YR) capture of the Huai River had a profound effect on the landscape evolution,ecology, and social development in China, disrupting the evolution of some vital shallow floodplain lakes.Because of the absence of lacustrine sediment provenance analysis, previous studies were inadequate in distinguishing the influence of YR capture on paleoenvironmental changes in these lakes, especially on landscape evolution, redox conditions, lake level changes, and organic productivity. The cur...  相似文献   

11.
We present a study of the textural signature of terrestrial weathering and related biological activity in the Tatahouine meteorite. Scanning and transmission electron microscopy images obtained on the weathered samples of the Tatahouine meteorite and surrounding soil show two types of bacteria-like forms lying on mineral surfaces: (1) rod-shaped forms (RSF) about 70-80 nm wide and ranging from 100 nm to 600 nm in length; (2) ovoid forms (OVF) with diameters between 70 and 300 nm. They look like single cells surrounded by a cell wall. Only Na, K, C, O and N with traces of P and S are observed in the bulk of these objects. The chemical analyses and electron diffraction patterns confirm that the RSF and OVF cannot be magnetite or other iron oxides, iron hydroxides, silicates or carbonates. The sizes of the RSF and OVF are below those commonly observed for bacteria but are very similar to some bacteria-like forms described in the Martian meteorite ALH84001. All the previous observations strongly suggest that they are bacteria or their remnants. This conclusion is further supported by microbiological experiments in which pleomorphic bacteria with morphology similar to the OVF and RSF objects are obtained from biological culture of the soil surrounding the meteorite pieces. The present results show that bacteriomorphs of diameter less than 100 nm may in fact represent real bacteria or their remnants.  相似文献   

12.
One of the principal reasons why speleothems are recognised as important palaeoclimate archives is their suitability for accurate and precise uranium-series (U-series) age determination. Sampling speleothem sections for U-series dating is straightforward in most cases because visible growth layers are preserved. However, this is not always the case, and here we describe a sampling strategy whereby growth layers are resolved from trace-element images produced by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We apply this method to a section of an Italian subaqueous speleothem (CD3) that lacks persistent visible growth layering.Trace-element imaging revealed growth layers that are strongly non-planar in their geometry owing to the speleothem's pronounced euhedral crystal terminations. The most prominent trace-element layers were first digitized as x, y vector contours. We then interpolated these in the growth-axis direction to generate a series of contour lines at ∼250-μm increments. The coordinates of these contours were used to guide the sampling via a computerised micromilling lathe. This produced a total of 22 samples for U-series dating by multi-collector ICP-MS. The dating results returned ages in correct stratigraphic order within error. Close inspection of the U-series data and the derived depth–age model suggests that the main source of model-age uncertainty is unrelated to the contour sampling but instead more associated with how closely spaced the model ages are in time, i.e. the model age density. Comparisons between stable oxygen and carbon isotope profiles derived from aliquots of the dating samples and two other stable isotope profiles from CD3 spanning the same time period compare very favourably. Taken together, this suggests that our trace-element contouring method provides a reliable means for extracting samples for dating (and other geochemical analyses), and can be applied to similar speleothems lacking visible growth layering.  相似文献   

13.
Abstract

A two-parameter gamma distribution for synthetic unit hydrographs (SUH) is compared with the Clark's and Espey's SUHs. A critical comparison of Clark's and gamma UHs, in terms of recession characteristics and time–area curve, is presented. It is observed that, in principle, a gamma UH can represent the hydrograph recession better than the Clark's UH does. Selection of a time–area curve is needed for obtaining the Clark's UH. The main problem in developing a SUH using the Clark's method is identified as the non-availability of a parametric form of the time–area curve. The time–area curve as represented in the hydrological model HEC-1, for the use in Clark's method, is found inadequate and unjustified. Gamma UHs obtained without optimization, for several examples, are found consistent with their physical meanings and better than the respective Clark's UH in reproducing runoff obtained with optimization. The parameters of Clark's UH (i.e. time of concentration and recession constant), as optimized through the HEC-1 program, are found inconsistent with their empirical origins and physical meanings; these lose their physical meaning and serve only as fitting parameters. This is due to the inappropriate time–area curve. A gamma UH has also the advantage of having fewer parameters than Clark's UH, which makes it more identifiable while still maintaining a connection with the physics of the problem. Espey's SUH for urban watersheds is transmuted to a gamma distribution using the empirical equations for the peak and time to peak of the UH. A numerical UH for a gauged catchment, generally obtained through linear programming or a least-squares approach, can be easily transmuted to a gamma UH and, hence, can be given a conceptual interpretation. Thus, these can also be used for developing a SUH.  相似文献   

14.
Optimal electromagnetic wave propagation velocities and subsurface images for ground-penetrating radar (GPR) data can be specified by using an imaging scanning method. In addition to time-migrating the unmigrated GPR section, we remigrate the already time-migrated section by a one-step remigration operator using different velocities. This creates many time-migrated images for different constant migration velocities. In this way, the computation time for time-migration is very much reduced. Time-migrated reflector images `propagate' when the constant migration velocity is continuously changed. For this `propagation' there exists a wave-equation-type partial differential equation. Each time-migrated section can thus be viewed as a snapshot for a certain migration velocity. The time-migrated reflector images behave like `waves', called image waves. This is applied to real GPR data acquired over a concrete body within which a steel cable frame is buried. The method produces a quick velocity scan to find a reliable migration velocity leading to the best time-migrated image.  相似文献   

15.
What hydraulic information can be gained from remotely sensed observations of a river's surface? In this study, we analyze the relationship between river bed undulations and water surfaces for an ungauged reach of the Xingu River, a first‐order tributary of the Amazon river. This braided reach is crosscut more than 10 times by a ENVISAT (ENVironmental SATellite) track that extends over 100 km. Rating curves based on a modeled discharge series and altimetric measurements are used, including the zero‐flow depth Z 0 parameter, which describes river's bathymetry. River widths are determined from JERS (Japanese Earth Ressources Satellite) images. Hydrodynamic laws predict that irregularities in the geometry of a river bed produce spatial and temporal variations in the water level, as well as in its slope. Observation of these changes is a goal of the Surface Water and Ocean Topography satellite mission, which has a final objective of determining river discharge. First, the concept of hydraulic visibility is introduced, and the seasonality of water surface slope is highlighted along with different flow regimes and reach behaviors. Then, we propose a new single‐thread effective hydraulic approach for modeling braided rivers flows, based on the observation scales of current satellite altimetry. The effective hydraulic model is able to reproduce water surface elevations derived by satellite altimetry, and it shows that hydrodynamical signatures are more visible in areas where the river bed morphology varies significantly and for reaches with strong downstream control. The results of this study suggest that longitudinal variations of the slope might be an interesting criteria for the analysis of river segmentation into elementary reaches for the Surface Water Ocean Topography mission that will provide continuous measurements of the water surface elevations, the slopes, and the reach widths.  相似文献   

16.
Abstract

Several stream ordering and labeling methods have been proposed in order to describe some aspects of the geometry of river networks; namely, Horton's, Strahler's, Milton-Ollier's, Scheidegger's ordering techniques, and the STORET location coding system. This paper analyzes the topological significance of each of these methods, that is, the amount of information on the topological structure of the net that they can yield. Horton's and Strahler's ordering methods give only numerical information on the distribution of channels among different classes (orders); Milton-Ollier's and Scheidegger's methods give more information, from the topological point of view, as the former assigns a unique label to each stream segment in a network, and the latter takes into account all junctions; the STORET system labels interconnections between channels, but does not use the concept of order and is therefore more suitable for other purposes than for the theoretical study of river nets.  相似文献   

17.
Measurements from the Global Positioning System (GPS) satellites provide a valuable source of information about the ionosphere in the form of ray-path integrations of electron density. Total electron content (TEC) through the ionosphere can be estimated for specific satellite-to-ground paths using the two GPS frequencies and knowledge of the dispersive properties of the ionosphere. One approach used is the ionospheric imaging tool Multi Instrument Data Analysis System (MIDAS), which uses differential phase data from a number of GPS satellites and receivers to create an ionospheric movie of electron density. This paper addresses the accuracy with which MIDAS images the electron density at the F-layer peak. Firstly, the image accuracy is tested using a simulation of the imaging technique, representative of 1 year of data. Experimental GPS phase data are then used to image the electron density during a period of disturbed geomagnetic activity during April 2002. The images are compared to independent measurements from three ionosondes located across Europe and confirm the underestimate in peak electron density that was found in the simulation. Regardless of the peak density errors the vertical TEC in the images remains accurate. The accuracy of the imaged peak electron density is shown to improve across the image when measurements from ionosondes are included in the inversion process.  相似文献   

18.
Diverse technologies have been developed and tested for their efficacy in remediating perchlorate-contaminated surface water, groundwater, and soil. Biological reduction, particularly when coupled with electron donor augmentation, has been shown to be one of the most cost-effective alternatives. Numerous electron donors have been evaluated in the literature, but few studies have compared standard vs. slow-release electron donors for sequential nitrate and perchlorate reduction. This study evaluated the efficacy and kinetics of biological reduction in soil microcosms augmented with emulsified oil (EO), glycerol, and mulch extract. Results indicated that EO and glycerol spiked at approximately 100 times stoichiometric excess (i.e., 100x) achieved similar overall reductions and degradation rates for nitrate and perchlorate, although nitrate appeared to exhibit zero order kinetics while perchlorate exhibited first order kinetics. The zero order rate constants for nitrate reduction were 3.32 mg/L d and 2.57 mg/L d for EO and glycerol, respectively. The first order rate constant for perchlorate reduction was 0.36 day−1 for both EO and glycerol. Stable chemical oxygen demand (COD) concentrations also highlighted the slow-release properties of EO, which would reduce electron donor consumption in comparison to soluble substrates in soil remediation applications. The microcosms augmented with mulch extract failed to demonstrate any nitrate or perchlorate reduction due to the extract's lower COD concentration. Augmentation with compost or additional processing (i.e., concentration) would be necessary to make the extract a viable alternative.  相似文献   

19.
Ground-based dual-frequency GPS observations can be used to create images of electron density. This is well established for the Arctic ionosphere; here one of the first results is presented for the Antarctic. In this study, the GPS receivers in the Antarctic are supplemented with another GPS receiver onboard CHAMP. The aim of the study is to demonstrate the technique for investigating geophysical events, for example, an ionospheric disturbance period on 11 February 2004. The images have been validated by in-situ measurements from DMSP and CHAMP satellites, as well as Super Dual Auroral Radar Network (SuperDARN) convection patterns, which are able to confirm the location, presence, and transportation of large-scale plasma patches. This study indicates that although the convection still dominates in the high-latitude ionosphere, soft precipitation within the polar cap may play a role in the evolution of the polar patches. It also illustrates the potential for future multi-instrument studies of the Antarctic.  相似文献   

20.
The performances of a finite volume model (SFV) and finite element model (TELEMAC‐2D) in reproducing inundation on a 16 km reach of the river Severn, United Kingdom, are compared. Predicted inundation extents are compared with 4 airborne synthetic aperture radar images of a major flood event in November 2000, and these are used to calibrate 2 values of Manning's n for the channel and floodplain. The four images are shown to have different capacities to constrain roughness parameters, with the image acquired at low flow rate doing better in determining these parameters than the image acquired at approximately peak flow. This is assigned to the valley filling nature of the flood and the associated insensitivity of flood extent to changes in water level. The level of skill demonstrated by the models, when compared with inundation derived using a horizontal water free surface, also increases as flow rate drops. The two models show markedly different behaviours to the calibration process, with TELEMAC showing less sensitivity and lower optimum values for Manning's n than SFV. When the models are used in predictive mode, calibrated against one image and predicting another, SFV performs better than TELEMAC. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

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