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排序方式: 共有131条查询结果,搜索用时 765 毫秒
31.
T. Berkefeld W. Schmidt D. Soltau A. Bell H. P. Doerr B. Feger R. Friedlein K. Gerber F. Heidecke T. Kentischer O. v.?d. L??he M. Sigwarth E. W?lde P. Barthol W. Deutsch A. Gandorfer D. Germerott B. Grauf R. Meller A. ??lvarez-Herrero M. Kn?lker V. Mart??nez Pillet S. K. Solanki A. M. Title 《Solar physics》2011,268(1):103-123
This paper describes the wave-front correction system developed for the Sunrise balloon telescope, and it provides information about its in-flight performance. For the correction of low-order aberrations, a Correlating Wave-Front Sensor (CWS) was used. It consisted of a six-element Shack??C?Hartmann wave-front sensor (WFS), a fast tip-tilt mirror for the compensation of image motion, and an active telescope secondary mirror for focus correction. The CWS delivered a stabilized image with a precision of 0.04?arcsec (rms), whenever the coarse pointing was better than ???45?arcsec peak-to-peak. The automatic focus adjustment maintained a focus stability of 0.01?waves in the focal plane of the CWS. During the 5.5?day flight, good image quality and stability were achieved during 33?hours, containing 45?sequences, which lasted between 10 and 45?min. 相似文献
32.
Geostatistical models should be checked to ensure consistency with conditioning data and statistical inputs. These are minimum
acceptance criteria. Often the first and second-order statistics such as the histogram and variogram of simulated geological
realizations are compared to the input parameters to check the reasonableness of the simulation implementation. Assessing
the reproduction of statistics beyond second-order is often not considered because the “correct” higher order statistics are
rarely known. With multiple point simulation (MPS) geostatistical methods, practitioners are now explicitly modeling higher-order
statistics taken from a training image (TI). This article explores methods for extending minimum acceptance criteria to multiple
point statistical comparisons between geostatistical realizations made with MPS algorithms and the associated TI. The intent
is to assess how well the geostatistical models have reproduced the input statistics of the TI; akin to assessing the histogram
and variogram reproduction in traditional semivariogram-based geostatistics. A number of metrics are presented to compare
the input multiple point statistics of the TI with the statistics of the geostatistical realizations. These metrics are (1)
first and second-order statistics, (2) trends, (3) the multiscale histogram, (4) the multiple point density function, and
(5) the missing bins in the multiple point density function. A case study using MPS realizations is presented to demonstrate
the proposed metrics; however, the metrics are not limited to specific MPS realizations. Comparisons could be made between
any reference numerical analogue model and any simulated categorical variable model. 相似文献
33.
Amir H. Hosseini Clayton V. Deutsch Kevin W. Biggar Carl A. Mendoza 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(5):735-749
The spatial distribution of residual light non-aqueous phase liquid (LNAPL) is an important factor in reactive solute transport
modeling studies. There is great uncertainty associated with both the areal limits of LNAPL source zones and smaller scale
variability within the areal limits. A statistical approach is proposed to construct a probabilistic model for the spatial
distribution of residual NAPL and it is applied to a site characterized by ultra-violet-induced-cone-penetration testing (CPT–UVIF).
The uncertainty in areal limits is explicitly addressed by a novel distance function (DF) approach. In modeling the small-scale
variability within the areal limits, the CPT–UVIF data are used as primary source of information, while soil texture and distance
to water table are treated as secondary data. Two widely used geostatistical techniques are applied for the data integration,
namely sequential indicator simulation with locally varying means (SIS–LVM) and Bayesian updating (BU). A close match between
the calibrated uncertainty band (UB) and the target probabilities shows the performance of the proposed DF technique in characterization
of uncertainty in the areal limits. A cross-validation study also shows that the integration of the secondary data sources
substantially improves the prediction of contaminated and uncontaminated locations and that the SIS–LVM algorithm gives a
more accurate prediction of residual NAPL contamination. The proposed DF approach is useful in modeling the areal limits of
the non-stationary continuous or categorical random variables, and in providing a prior probability map for source zone sizes
to be used in Monte Carlo simulations of contaminant transport or Monte Carlo type inverse modeling studies. 相似文献
34.
The increasing use of unstructured grids for reservoir modeling motivates the development of geostatistical techniques to
populate them with properties such as facies proportions, porosity and permeability. Unstructured grids are often populated
by upscaling high-resolution regular grid models, but the size of the regular grid becomes unreasonably large to ensure that
there is sufficient resolution for small unstructured grid elements. The properties could be modeled directly on the unstructured
grid, which leads to an irregular configuration of points in the three-dimensional reservoir volume. Current implementations
of Gaussian simulation for geostatistics are for regular grids. This paper addresses important implementation details involved
in adapting sequential Gaussian simulation to populate irregular point configurations including general storage and computation
issues, generating random paths for improved long range variogram reproduction, and search strategies including the superblock
search and the k-dimensional tree. An efficient algorithm for computing the variogram of very large irregular point sets is developed for
model checking. 相似文献
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Mathematical Geosciences - Mineral resource estimation is an integral part of making informed decisions while evaluating a mining operation’s feasibility. Geostatistical tools estimate... 相似文献
40.
In geostatistics, most stochastic algorithm for simulation of categorical variables such as facies or rock types require a
conditional probability distribution. The multivariate probability distribution of all the grouped locations including the
unsampled location permits calculation of the conditional probability directly based on its definition. In this article, the
iterative proportion fitting (IPF) algorithm is implemented to infer this multivariate probability. Using the IPF algorithm,
the multivariate probability is obtained by iterative modification to an initial estimated multivariate probability using
lower order bivariate probabilities as constraints. The imposed bivariate marginal probabilities are inferred from profiles
along drill holes or wells. In the IPF process, a sparse matrix is used to calculate the marginal probabilities from the multivariate
probability, which makes the iterative fitting more tractable and practical. This algorithm can be extended to higher order
marginal probability constraints as used in multiple point statistics. The theoretical framework is developed and illustrated
with estimation and simulation example. 相似文献