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Els Verfaillie Steven Degraer Kristien Schelfaut Wouter Willems Vera Van Lancker 《Estuarine, Coastal and Shelf Science》2009
Mapping ecologically relevant zones in the marine environment has become increasingly important. Biological data are however often scarce and alternatives are being sought in optimal classifications of abiotic variables. The concept of ‘marine landscapes’ is based on a hierarchical classification of geological, hydrographic and other physical data. This approach is however subject to many assumptions and subjective decisions. 相似文献
53.
L. Origlia E. Valenti R. M. Rich 《Monthly notices of the Royal Astronomical Society》2005,356(4):1276-1282
Using the Near Infrared Spectrometer (NIRSPEC) spectrograph at Keck II, we have obtained infrared (IR) echelle spectra covering the range 1.5 –1.8 μm for the moderately reddened bulge globular clusters NGC 6342 and 6528, finding [Fe/H]=−0.60 and −0.17 dex, respectively. We measure an average α-enhancement of ≈+0.33 dex in both clusters, consistent with previous measurements on other metal-rich bulge clusters, and favouring the scenario of a rapid bulge formation and chemical enrichment. We also measure very low 12 C/13 C isotopic ratios (≈5 in NGC 6342 and ≈8 in NGC 6528), suggesting that extra-mixing mechanisms resulting from cool bottom processing are at work during evolution along the red giant branch (RGB). 相似文献
54.
Indicator Kriging without Order Relation Violations 总被引:2,自引:1,他引:1
Raimon Tolosana-Delgado Vera Pawlowsky-Glahn Juan-Jose Egozcue 《Mathematical Geosciences》2008,40(3):327-347
Indicator kriging (IK) is a spatial interpolation technique aimed at estimating the conditional cumulative distribution function
(ccdf) of a variable at an unsampled location. Obtained results form a discrete approximation to this ccdf, and its corresponding
discrete probability density function (cpdf) should be a vector, where each component gives the probability of an occurrence
of a class. Therefore, this vector must have positive components summing up to one, like in a composition in the simplex.
This suggests a simplicial approach to IK, based on the algebraic-geometric structure of this sample space: simplicial IK
actually works with log-odds. Interpolated log-odds can afterwards be easily re-expressed as the desired cpdf or ccdf. An
alternative but equivalent approach may also be based on log-likelihoods. Both versions of the method avoid by construction
all conventional IK standard drawbacks: estimates are always within the (0,1) interval and present no order-relation problems
(either with kriging or co-kriging). Even the modeling of indicator structural functions is clarified. 相似文献
55.
Ben Yang Yun Qian Larry K. Berg Po-Lun Ma Sonia Wharton Vera Bulaevskaya Huiping Yan Zhangshuan Hou William J. Shaw 《Boundary-Layer Meteorology》2017,162(1):117-142
We evaluate the sensitivity of simulated turbine-height wind speeds to 26 parameters within the Mellor–Yamada–Nakanishi–Niino (MYNN) planetary boundary-layer scheme and MM5 surface-layer scheme of the Weather Research and Forecasting model over an area of complex terrain. An efficient sampling algorithm and generalized linear model are used to explore the multiple-dimensional parameter space and quantify the parametric sensitivity of simulated turbine-height wind speeds. The results indicate that most of the variability in the ensemble simulations is due to parameters related to the dissipation of turbulent kinetic energy (TKE), Prandtl number, turbulent length scales, surface roughness, and the von Kármán constant. The parameter associated with the TKE dissipation rate is found to be most important, and a larger dissipation rate produces larger hub-height wind speeds. A larger Prandtl number results in smaller nighttime wind speeds. Increasing surface roughness reduces the frequencies of both extremely weak and strong airflows, implying a reduction in the variability of wind speed. All of the above parameters significantly affect the vertical profiles of wind speed and the magnitude of wind shear. The relative contributions of individual parameters are found to be dependent on both the terrain slope and atmospheric stability. 相似文献
56.
Ute C. Herzfeld Craig S. Lingle Cecily Freeman Chris A. Higginson Michael P. Lambert Li-Her Lee Vera A. Voronina 《Mathematical Geology》1997,29(6):859-890
The Antarctic Ice Sheet plays a major role in the global system, and the large ice streams discharging into the circumpolar
sea represent its gateways to the world’s oceans. Satellite radar altimeter data provide an opportunity for mapping surface
elevation at kilometerresolution with meteraccuracy. Geostaristical methods have been developed for the analysis of these
data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of Lambert
Glacier/Amery Ice Shelf, the largest ice stream in East Antarctica, has advanced 10–12 km between 1978 and 1987–89. The objectives
of this paper are to explore possibilities and limitations of satellite-altimetry-based mapping to capture changes for shorter
time windows and for smaller areas, and to investigate some methodological aspects of the data analysis. We establish that
one season of radar altimeter data is sufficient for constructing a map. This allows study of interannual variation and is
the key for a limeseries analysis approach to study changes in ice streams. Maps of the lower Lambert Glacier and the entire
Amery Ice Shelf are presented for austral winters 1978, 1987, 1988, and 1989. As a first step toward understanding the dynamics
of the ice-stream/iceshelf system, elevation changes are calculated for grounded ice, the grounding zone, and floating ice.
In the absence of (sufficient) surface gravity control for the Lambert Glacier/Amery Ice Shelf area, altimetry-based maps
may facilitate improvement of geoid models as they provide constraints on the terrain correction in the inverse gravimetric
problem. 相似文献
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