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11.
J.I. Lunine C. Elachi S.D. Wall M.D. Allison R. Boehmer P. Encrenaz G. Franceschetti G. Hamilton W.T.K. Johnson R.L. Kirk R. Lorenz D.O. Muhleman S.J. Ostro P. Paillou F. Posa L.E. Roth S. Shaffer B. Stiles S. Vetrella C.A. Wood H. Zebker E. Karkoschka E. McFarlane B. Kazeminejad 《Icarus》2008,195(1):415-433
Cassini's third and fourth radar flybys, T7 and T8, covered diverse terrains in the high southern and equatorial latitudes, respectively. The T7 synthetic aperture radar (SAR) swath is somewhat more straightforward to understand in terms of a progressive poleward descent from a high, dissected, and partly hilly terrain down to a low flat plain with embayments and deposits suggestive of the past or even current presence of hydrocarbon liquids. The T8 swath is dominated by dunes likely made of organic solids, but also contain somewhat enigmatic, probably tectonic, features that may be partly buried or degraded by erosion or relaxation in a thin crust. The dark areas in T7 show no dune morphology, unlike the dark areas in T8, but are radiometrically warm like the dunes. The Huygens landing site lies on the edge of the T8 swath; correlation of the radar and Huygens DISR images allows accurate determination of its coordinates, and indicates that to the north of the landing site sit two large longitudinal dunes. Indeed, had the Huygens probe trajectory been just 10 km north of where it actually was, images of large sand dunes would have been returned in place of the fluvially dissected terrain actually seen—illustrating the strong diversity of Titan's landscapes even at local scales. 相似文献
12.
Heuristic models for indicator variograms and their parameters (practical nugget effect and range) are proposed for a bivariate normal distribution with spherical correlogram. These models can be used conveniently as a preliminary check for bivariate normality. In the general non-Gaussian case, indicator variogram models for multiple threshold values must verify a certain number of order relations (inequalities) established directly from the properties of a general bivariate cumulative distribution function. An interesting, little-known maximum hole effect for indicator correlation is pointed out. 相似文献
13.
Strict positive definiteness in geostatistics 总被引：1，自引：1，他引：0
S.?De IacoEmail authorView author&#;s OrcID profile D.?Posa 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(3):577-590
Geostatistical modeling is often based on the use of covariance functions, i.e., positive definite functions. However, when interpolation problems have to be solved, it is advisable to consider the subset of strictly positive definite functions. Indeed, it will be argued that ensuring strict positive definiteness for a covariance function is convenient from a theoretical and practical point of view. In this paper, an extensive analysis on strictly positive definite covariance functions has been given. The closure of the set of strictly positive definite functions with respect to the sum and the product of covariance functions defined on the same Euclidean dimensional space or on factor spaces, as well as on partially overlapped lower dimensional spaces, has been analyzed. These results are particularly useful (a) to extend strict positive definiteness in higher dimensional spaces starting from covariance functions which are only defined on lower dimensional spaces and/or are only strictly positive definite in lower dimensional spaces, (b) to construct strictly positive definite covariance functions in space–time as well as (c) to obtain new asymmetric and strictly positive definite covariance functions. 相似文献
14.
Conditioning of the stationary kriging matrices for some well-known covariance models 总被引：1，自引：0，他引：1
D. Posa 《Mathematical Geology》1989,21(7):755-765
In this paper, the condition number of the stationary kriging matrix is studied for some well-known covariance models. Indeed, the robustness of the kriging weights is strongly affected by this measure. Such an analysis can justify the choice of a covariance function among other admissible models which could fit a given experimental covariance equally well. 相似文献
15.
In this paper, entropy is presented as an alternative measure to characterize the bivariate distribution of a stationary spatial process. This non-parametric estimator attempts to quantify the concept of spatial ordering, and it provides a measure of how Gaussian the experimental bivariate distribution is. The concept of entropy is explained and the classical definition presented, along with some important results. In particular, the reader is reminded that, for a known mean and covariance, the bivariate Gaussian distribution maximizes entropy. A relative entropy estimator is introduced in order to measure departure of an experimental bivariate distribution from the bivariate Gaussian. Two case studies are presented as examples. 相似文献
16.
By extending the product and product–sum space-time covariance models, new families are generated as integrated products and product–sums. These include nonintegrable space-time covariance models not obtainable by the Cressie–Huang representation. It is shown how to fit the spatial and temporal components of the models as well as the probability density function. The methods are illustrated by a case study. 相似文献
17.
In this paper, the effect on Kriging weights of non-bias conditions, when the same residual covariance model is used, has been studied by the l2 norm of the weights difference between Ordinary Kriging and Kriging with a trend model. Four covariance models, in 1-D and 2-D, and in interpolation and extrapolation conditions are examined. Situations in which both algorithms yield the same results are pointed out. 相似文献
18.
The rhodophyte Compsopogon coeruleus (Balbis ex C. Agardh) Montagne is newly recorded from Fiji, South Pacific. Plants occur in dense masses in the Wainivesi River in the province of Tailevu. Local villagers collect the plants and use them to cook a “pudding” with tinned fish, very similar to “puddings” prepared by coastal Fijians using marine species such as Gracilaria and Hypnea. This is the first documented account of the use of Compsopogon as a gelling agent in the preparation of human food. 相似文献