共查询到20条相似文献，搜索用时 421 毫秒
1.
Alberto Malinverno 《Pure and Applied Geophysics》1989,131(1-2):139-155
Stochastic models can generate profiles that resemble topography by taking uncorrelated, zero-average noise as input, introducing some correlation in the time series of noise, and integrating the resulting correlated noise. The output profile will depict a nonstationary, randomly rough surface. Two models have been chosen for comparison: a fractal model, in which the noise is correlated even at large distances, and an autoregressive model of order 1, in which the correlation of the noise decays rapidly. Both models have as an end-member a random walk, which is the integration of uncorrelated noise. The models have been fitted to profiles of submarine topography, and the sample autocorrelation, power spectrum and variogram have been compared to the theoretical predictions. The results suggest that a linear system approach is a viable method to model and classify sea-floor topography. The comparison does not show substantial disagreement of the data with either the autoregressive or the fractal model, although a fractal model seems to give a better fit. However, the amplitudes predicted by a nonstationary fractal model for long wavelengths (of the order of 1000 km) are unreasonably large. When viewed through a large window, ocean floor topography is likely to have an expected value determined by isostasy, and to be stationary. Nonstationary models are best applied to wavelengths of the order of 100 km or less. 相似文献
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We analyze the impact of the choice of the variogram model adopted to characterize the spatial variability of natural log-transmissivity on the evaluation of leading (statistical) moments of hydraulic heads and contaminant travel times and trajectories within mildly (randomly) heterogeneous two-dimensional porous systems. The study is motivated by the fact that in several practical situations the differences between various variogram types and a typical noisy sample variogram are small enough to suggest that one would often have a hard time deciding which of the tested models provides the best fit. Likewise, choosing amongst a set of seemingly likely variogram models estimated by means of geostatistical inverse models of flow equations can be difficult due to lack of sensitivity of available model discrimination criteria. We tackle the problem within the framework of numerical Monte Carlo simulations for mean uniform and radial flow scenarios. The effect of three commonly used isotropic variogram models, i.e., Gaussian, Exponential and Spherical, is analyzed. Our analysis clearly shows that (ensemble) mean values of the quantities of interest are not considerably influenced by the variogram shape for the range of parameters examined. Contrariwise, prediction variances of the quantities examined are significantly affected by the choice of the variogram model of the log-transmissivity field. The spatial distribution of the largest/lowest values of the relative differences observed amongst the tested models depends on a combination of variogram shape and parameters and relative distance from internal sources and the outer domain boundary. Our findings suggest the need of developing robust techniques to discriminate amongst a set of seemingly equally likely alternative variogram models in order to provide reliable uncertainty estimates of state variables. 相似文献
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There are two basic approaches for estimating flood quantiles: a parametric and a nonparametric method. In this study, the comparisons of parametric and nonparametric models for annual maximum flood data of Goan gauging station in Korea were performed based on Monte Carlo simulation. In order to consider uncertainties that can arise from model and data errors, kernel density estimation for fitting the sampling distributions was chosen to determine safety factors (SFs) that depend on the probability model used to fit the real data. The relative biases of Sheater and Jones plug-in (SJ) are the smallest in most cases among seven bandwidth selectors applied. The relative root mean square errors (RRMSEs) of the Gumbel (GUM) are smaller than those of any other models regardless of parent models considered. When the Weibull-2 is assumed as a parent model, the RRMSEs of kernel density estimation are relatively small, while those of kernel density estimation are much bigger than those of parametric methods for other parent models. However, the RRMSEs of kernel density estimation within interpolation range are much smaller than those for extrapolation range in comparison with those of parametric methods. Among the applied distributions, the GUM model has the smallest SFs for all parent models, and the general extreme value model has the largest values for all parent models considered. 相似文献
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Saffet Erdogan 《地球表面变化过程与地形》2009,34(3):366-376
Digital elevation models have been used in many applications since they came into use in the late 1950s. It is an essential tool for applications that are concerned with the Earth's surface such as hydrology, geology, cartography, geomorphology, engineering applications, landscape architecture and so on. However, there are some differences in assessing the accuracy of digital elevation models for specific applications. Different applications require different levels of accuracy from digital elevation models. In this study, the magnitudes and spatial patterning of elevation errors were therefore examined, using different interpolation methods. Measurements were performed with theodolite and levelling. Previous research has demonstrated the effects of interpolation methods and the nature of errors in digital elevation models obtained with indirect survey methods for small‐scale areas. The purpose of this study was therefore to investigate the size and spatial patterning of errors in digital elevation models obtained with direct survey methods for large‐scale areas, comparing Inverse Distance Weighting, Radial Basis Functions and Kriging interpolation methods to generate digital elevation models. The study is important because it shows how the accuracy of the digital elevation model is related to data density and the interpolation algorithm used. Cross validation, split‐sample and jack‐knifing validation methods were used to evaluate the errors. Global and local spatial auto‐correlation indices were then used to examine the error clustering. Finally, slope and curvature parameters of the area were modelled depending on the error residuals using ordinary least regression analyses. In this case, the best results were obtained using the thin plate spline algorithm. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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The semi-empirical Kozeny–Carman (KC) equation is the most famous permeability–porosity relation, which is widely used in the field of flow in porous media and is the starting point for many other permeability models. However, this relation has many limitations from its inception, and the KC constant is an empirical parameter which was proved to be not a constant. In this paper, we briefly reviewed the KC equation, its modifications and various models for the KC constant. We then derived an analytical expression for the permeability in homogeneous porous media based on the fractal characters of porous media and capillary model. The proposed model is expressed as a function of fractal dimensions, porosity and maximum pore size. The analytical KC constant with no empirical constant is obtained from the assumption of square geometrical model. Furthermore, a distinct linear scaling law between the dimensionless permeability and porosity is found. It is also shown that our analytical permeability is more closely related to the microstructures (fractal dimensions, porosity and maximum pore size), compared to those obtained from conventional methods and models. 相似文献
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Adrian Chappell George L. Heritage Ian C. Fuller Andrew R. G. Large David J. Milan 《地球表面变化过程与地形》2003,28(4):349-370
A digital elevation model (DEM) of a fluvial environment represented landform surface variability well and provided a medium for monitoring morphological change over time. Elevation was measured above an arbitrary datum using a ground‐based three‐dimensional tacheometric survey in two reaches of the River Nent, UK, in July 1998, October 1998 (after flood conditions) and June 1999. A detailed geostatistical analysis of the elevation data was used to model the spatial variation of elevation and to produce DEMs in each reach and for each survey period. Maps of the difference in elevation were produced and volumetric change was calculated for each reach and each survey period. The parameters of variogram models were used to describe the morphological character of each reach and to elucidate the linkages between process and the form of channel change operating at different spatial and temporal scales. The analysis of channel change on the River Nent shows the potential of geostatistics for investigating the magnitude and frequency of geomorphic work in other rivers. A flood modified the channel features, but low magnitude and high frequency flows rationalized the morphology. In spite of relatively small amounts of net flux the channel features changed as a consequence of the reworking of existing material. The blocking of chute entrances and redirection of the channel had a considerable effect on the behaviour of the channel. Such small changes suggested that the distributary system was sensitive to variation in sediment regime. Plots of the kriging variances against sampling intervals were used to quantify the temporal variation in sampling redundancy (ranging between ?11 per cent and +93 per cent). These curves illustrated the importance of bespoke sampling designs to reduce sampling effort by incorporating anisotropic variation in space and geomorphic information on flow regime. Variation in the nugget parameter of the variogram models was interpreted as sampling inaccuracy caused by variability in particle size and is believed to be important for future work on surface roughness. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Accurate estimation of aquifer parameters, especially from crystalline hard rock area, assumes a special significance for management of groundwater resources. The aquifer parameters are usually estimated through pumping tests carried out on water wells. While it may be costly and time consuming for carrying out pumping tests at a number of sites, the application of geophysical methods in combination with hydro-geochemical information proves to be potential and cost effective to estimate aquifer parameters. Here a method to estimate aquifer parameters such as hydraulic conductivity, formation factor, porosity and transmissivity is presented by utilizing electrical conductivity values analysed via hydro-geochemical analysis of existing wells and the respective vertical electrical sounding (VES) points of Sindhudurg district, western Maharashtra, India. Further, prior to interpolating the distribution of aquifer parameters of the study area, variogram modelling was carried out using data driven techniques of kriging, automatic relevance determination based Bayesian neural networks (ARD-BNN) and adaptive neuro-fuzzy neural networks (ANFIS). In total, four variogram model fitting techniques such as spherical, exponential, ARD-BNN and ANFIS were compared. According to the obtained results, the spherical variogram model in interpolating transmissivity, ARD-BNN variogram model in interpolating porosity, exponential variogram model in interpolating aquifer thickness and ANFIS variogram model in interpolating hydraulic conductivity outperformed rest of the variogram models. Accordingly, the accurate aquifer parameters maps of the study area were produced by using the best variogram model. The present results suggest that there are relatively high value of hydraulic conductivity, porosity and transmissivity at Parule, Mogarne, Kudal, and Zarap, which would be useful to characterize the aquifer system over western Maharashtra. 相似文献
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Quantification of braided river channel change using archival digital image analysis 总被引：1，自引：0，他引：1
S. N. Lane P. E. Widdison R. E. Thomas P. J. Ashworth J. L. Best I. A. Lunt G. H. Sambrook Smith C. J. Simpson 《地球表面变化过程与地形》2010,35(8):971-985
Historical archives of grey‐scale river channel imagery are extensive. Here, we present and test a methodology to extract detailed quantitative topographic data from such imagery of sand‐bed rivers. Extracting elevation information from rivers is difficult as they are characterized by a low relative relief (<4 m); the area of interest may be spatially extensive (e.g. active channel widths >500 m in large braided rivers); the rate of change of surface elevation is generally low except in the vicinity of individual channel banks where the rate of change is very high; there is the complication that comes from inundation; and there may be an added complication caused by blockage of the field of view by vegetation. Here, we couple archival photogrammetric techniques with image processing methods and test these for quantification of sand‐bed braided river dynamics, illustrated for a 500 m wide, 3 km long reach of the South Saskatchewan River, Canada. Digital photogrammetry was used to quantify dry areas and water edge elevations. A methodology was then used to calibrate the spectral signature of inundated areas by combining established two media digital photogrammetric methods and image matching. This allowed determination of detailed depth maps for inundated areas and, when combined with dry area data, creation of complete digital elevation models. Error propagation methods were used to determine the erosion and deposition depths detectable from sequential digital elevation models. The result was a series of elevation models that demonstrate the potential for acquiring detailed and precise elevation data from any historical aerial imagery of rivers without needing associated calibration data, provided that imagery is of the necessary scale to capture the features of interest. We use these data to highlight several aspects of channel change on the South Saskatchewan River, including bar movement, bank erosion and channel infilling. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Kuo-Chin Hsu Kuan-Chih Chen 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(7):1053-1065
This paper proposes a multiscale flow and transport model which can be used in three-dimensional fractal random fields. The
fractal random field effectively describes a field with a high degree of variability to satisfy the one-point statistics of
Levy-stable distribution and the two-point statistics of fractional Levy motion (fLm). To overcome the difficulty of using
infinite variance of Levy-stable distribution and to provide the physical meaning of a finite domain in real space, truncated
power variograms are utilized for the fLm fields. The fLm model is general in the sense that both stationary and commonly
used fractional Brownian motion (fBm) models are its special cases. When the upper cutoff of the truncated power variogram
is close to the lower cutoff, the stationary model is well approximated. The commonly used fBm model is recovered when the
Levy index of fLm is 2. Flow and solute transport were analyzed using the first-order perturbation method. Mean velocity,
velocity covariance, and effective hydraulic conductivity in a three-dimensional fractal random field were derived. Analytical
results for particle displacement covariance and macrodispersion coefficients are also presented. The results show that the
plume in an fLm field moves slower at early time and has more significant long-tailing behavior at late time than in fBm or
stationary exponential fields. The proposed fractal transport model has broader applications than those of stationary and
fBm models. Flow and solute transport can be simulated for various scenarios by adjusting the Levy index and cutoffs of fLm
to yield more accurate modeling results. 相似文献
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Automated digital photogrammetry was used to produce digital elevation models of experimental model landscapes under controlled laboratory conditions as part of a series of rainfall erosion experiments looking at the evolution of landforms in response to erosion. The method allowed the elevations of the experimental landscapes to be studied in great detail on a regular grid digital terrain map with relatively very little effort. Digital photogrammetry produced elevation data at a resolution of 6 mm with a standard deviation of 2·0 mm over an experimental catchment relief of approximately 200 mm; this resolution is considerably better than that achievable by conventional manual photogrammetry. The density of grid points was sufficiently high that small‐scale details such as knickpoints developing in channels were represented. The method can facilitate the study of both experimental and natural landscapes in great detail. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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RESEARCH ON THE RELATIONSHIP BETWEEN FRACTAL FACTORS AND TECTONIC ACTIVITY——A CASE STUDY OF SOUTHWESTERN YUNNAN BLOCK 
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下载免费PDF全文 Geomorphology could record long-term accumulation of tectonic movement and quantify it by relevant parameters.But because the influences of other factors such as climate and lithology,how to use the relevant parameters to reveal the relationship between geomorphology and tectonics is a research hot spot.In this paper,we utilize the variogram method and the cellular fractal model to estimate parameters such as the fractal dimension (D) and ordinate intercept (γ) from the SRTM3 DEM using a moving window operation.We compare the distribution characteristics of the parameters in different climate and lithology.The results indicate that the correlation between the parameters and lithology or climate is very poor.The fractal dimension (D) reveals a very good correlation with tectonics,which is low in tectonically inactive areas and high in active areas.It implies that fractal dimension (D) may be a new method for research of regional tectonic movement. 相似文献
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H. Murat Yilmaz 《地球表面变化过程与地形》2007,32(9):1346-1361
Mappings of the earth surface and their representation in 3D (three‐dimensional) models are commonly used in most recent research. Modeling research, which starts with classical surveying methods, acquires new dimensions matching the modern technologies. 3D models of any object or earth surface can be used in much visual and scientific research. A digital model of the landscape is an important part within creation of geo‐information systems used in the public administration and in the commercial sphere. It is an important tool in applications such as geomorphology, hydrology, geology, cartography, ecology, mining etc. Values of volume in terrains that do not have regular geometric structure can be obtained more accurately by using 3D models of surfaces with respect to developing technology. Basic data of 3D models must indicate 3D coordinates of the surveyed object in the reference frame. Distribution and intensity of points are important factors in modeling earth surfaces. A minimum number of points is desired in defining an object in 3D. Interpolation methods employing different mathematical models are used to obtain 3D models of terrain surfaces. In this study, the effect of interpolation methods in defining a terrain surface is investigated. For this purpose, a uniform surface, hill‐shaped artificial object with a known volume is employed. The 3D surface and volume are calculated by using 12 different interpolation methods. Point distribution, point intensity and accuracy of point measurements are not considered. The same data set was used for all the interpolation methods. The interpolation methods are compared and evaluated based on the results. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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A simple algorithm for generating streamflow networks for macroscale hydrological models (MHMs) from digital elevation models (DEMs) is presented. Typically these hydrological models are grid based, with the simulated runoff produced within each cell routed through a stream network which connects the centers of cells in the direction of the major streams. Construction of such stream networks is a time consuming task, which has generally been done by hand with the aid of maps. Results indicate that the algorithm works satisfactorily in areas of both high and low relief, and for a wide range of model cell resolutions, although some manual adjustments may be necessary. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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Advances in spatial analytical software allow digital elevation models (DEMs) to be produced which accurately represent landform surface variability and offer an important opportunity to measure and monitor morphological change and sediment transfer across a variety of spatial scales. Many of the techniques presently employed (aerial LIDAR, EDM theodolites, GPS, photogrammetry) suffer coverage or resolution limitations resulting in a trade‐off between spatial coverage and morphologic detail captured. This issue is particularly important when rates of spatial and temporal change are considered for fluvial systems. This paper describes the field and processing techniques required for oblique laser scanning to acquire 0·01 m resolution digital elevation data of an upland reach of the River Wharfe in the UK. The study site is variable with rapidly changing morphology, diverse vegetation and the presence of water, and these are evaluated with respect to laser data accuracy. Scan location, frequency and distance are discussed with reference to survey accuracy and efficiency, and a field protocol is proposed. Scan data cloud merging was achieved with a high degree of precision (sub‐centimetre) and positional data are shown to be very accurate for exposed surfaces. Vegetation and water decrease the accuracy, as the laser pulse is often prevented from reaching the ground surface or is not returned. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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With the introduction of high‐resolution digital elevation models, it is possible to use digital terrain analysis to extract small streams. In order to map streams correctly, it is necessary to remove errors and artificial sinks in the digital elevation models. This step is known as preprocessing and will allow water to move across a digital landscape. However, new challenges are introduced with increasing resolution because the effect of anthropogenic artefacts such as road embankments and bridges increases with increased resolution. These are problematic during the preprocessing step because they are elevated above the surrounding landscape and act as artificial dams. The aims of this study were to evaluate the effect of different preprocessing methods such as breaching and filling on digital elevation models with different resolutions (2, 4, 8, and 16 m) and to evaluate which preprocessing methods most accurately route water across road impoundments at actual culvert locations. A unique dataset with over 30,000 field‐mapped road culverts was used to assess the accuracy of stream networks derived from digital elevation models using different preprocessing methods. Our results showed that the accuracy of stream networks increases with increasing resolution. Breaching created the most accurate stream networks on all resolutions, whereas filling was the least accurate. Burning streams from the topographic map across roads from the topographic map increased the accuracy for all methods and resolutions. In addition, the impact in terms of change in area and absolute volume between original and preprocessed digital elevation models was smaller for breaching than for filling. With the appropriate methods, it is possible to extract accurate stream networks from high‐resolution digital elevation models with extensive road networks, thus providing forest managers with stream networks that can be used when planning operations in wet areas or areas near streams to prevent rutting, sediment transport, and mercury export. 相似文献
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Influence of pit removal methods on river network position 总被引：1，自引：1，他引：0
Digital elevation models often contain depressions that result in areas described as having no drainage, referred to as sinks or pits. These depressions disrupt the drainage surface, which disrupt routing of flow over the surface. Most of the attributes that can be extracted from a digital elevation model rely on flow‐routing algorithms to calculate the upslope contributing area. There is little information on the influence of the various algorithms on the position and on the connectivity of the extracted networks. The aim of this study was to assess the effects of pit removal methods, data sources and flow‐routing algorithms on the position of river networks. The results show that all factors and methods have an impact on the position of the extracted networks. The pit removal method combining filling and carving extracted river networks closer to the reference, as well the elevation models with higher resolution. Single‐flow direction methods provided more accurate positioning of river network, in this test area where the drainage is generally well defined. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献