6,413 research outputs found
Management and display of four-dimensional environmental data sets using McIDAS
Over the past four years, great strides have been made in the areas of data management and display of 4-D meteorological data sets. A survey was conducted of available and planned 4-D meteorological data sources. The data types were evaluated for their impact on the data management and display system. The requirements were analyzed for data base management generated by the 4-D data display system. The suitability of the existing data base management procedures and file structure were evaluated in light of the new requirements. Where needed, new data base management tools and file procedures were designed and implemented. The quality of the basic 4-D data sets was assured. The interpolation and extrapolation techniques of the 4-D data were investigated. The 4-D data from various sources were combined to make a uniform and consistent data set for display purposes. Data display software was designed to create abstract line graphic 3-D displays. Realistic shaded 3-D displays were created. Animation routines for these displays were developed in order to produce a dynamic 4-D presentation. A prototype dynamic color stereo workstation was implemented. A computer functional design specification was produced based on interactive studies and user feedback
Simultaneous Coherent Structure Coloring facilitates interpretable clustering of scientific data by amplifying dissimilarity
The clustering of data into physically meaningful subsets often requires
assumptions regarding the number, size, or shape of the subgroups. Here, we
present a new method, simultaneous coherent structure coloring (sCSC), which
accomplishes the task of unsupervised clustering without a priori guidance
regarding the underlying structure of the data. sCSC performs a sequence of
binary splittings on the dataset such that the most dissimilar data points are
required to be in separate clusters. To achieve this, we obtain a set of
orthogonal coordinates along which dissimilarity in the dataset is maximized
from a generalized eigenvalue problem based on the pairwise dissimilarity
between the data points to be clustered. This sequence of bifurcations produces
a binary tree representation of the system, from which the number of clusters
in the data and their interrelationships naturally emerge. To illustrate the
effectiveness of the method in the absence of a priori assumptions, we apply it
to three exemplary problems in fluid dynamics. Then, we illustrate its capacity
for interpretability using a high-dimensional protein folding simulation
dataset. While we restrict our examples to dynamical physical systems in this
work, we anticipate straightforward translation to other fields where existing
analysis tools require ad hoc assumptions on the data structure, lack the
interpretability of the present method, or in which the underlying processes
are less accessible, such as genomics and neuroscience
On the non-local geometry of turbulence
A multi-scale methodology for the study of the non-local geometry of eddy structures in turbulence is developed. Starting from a given three-dimensional field, this consists of three main steps: extraction, characterization and classification of structures. The extraction step is done in two stages. First, a multi-scale decomposition based on the curvelet transform is applied to the full three-dimensional field, resulting in a finite set of component three-dimensional fields, one per scale. Second, by iso-contouring each component field at one or more iso-contour levels, a set of closed iso-surfaces is obtained that represents the structures at that scale. The characterization stage is based on the joint probability density function (p.d.f.), in terms of area coverage on each individual iso-surface, of two differential-geometry properties, the shape index and curvedness, plus the stretching parameter, a dimensionless global invariant of the surface. Taken together, this defines the geometrical signature of the iso-surface. The classification step is based on the construction of a finite set of parameters, obtained from algebraic functions of moments of the joint p.d.f. of each structure, that specify its location as a point in a multi-dimensional ‘feature space’. At each scale the set of points in feature space represents all structures at that scale, for the specified iso-contour value. This then allows the application, to the set, of clustering techniques that search for groups of structures with a common geometry. Results are presented of a first application of this technique to a passive scalar field obtained from 5123 direct numerical simulation of scalar mixing by forced, isotropic turbulence (Reλ = 265). These show transition, with decreasing scale, from blob-like structures in the larger scales to blob- and tube-like structures with small or moderate stretching in the inertial range of scales, and then toward tube and, predominantly, sheet-like structures with high level of stretching in the dissipation range of scales. Implications of these results for the dynamical behaviour of passive scalar stirring and mixing by turbulence are discussed
Oceanic three-dimensional Lagrangian Coherent Structures: A study of a mesoscale eddy in the Benguela ocean region
We study three dimensional oceanic Lagrangian Coherent Structures (LCSs) in
the Benguela region, as obtained from an output of the ROMS model. To do that
we first compute Finite-Size Lyapunov exponent (FSLE) fields in the region
volume, characterizing mesoscale stirring and mixing. Average FSLE values show
a general decreasing trend with depth, but there is a local maximum at about
100 m depth. LCSs are extracted as ridges of the calculated FSLE fields. They
present a "curtain-like" geometry in which the strongest attracting and
repelling structures appear as quasivertical surfaces. LCSs around a particular
cyclonic eddy, pinched off from the upwelling front are also calculated. The
LCSs are confirmed to provide pathways and barriers to transport in and out of
the eddy
Reducing Occlusion in Cinema Databases through Feature-Centric Visualizations
In modern supercomputer architectures, the I/O capabilities do not keep up with the computational speed. Image-based techniques are one very promising approach to a scalable output format for visual analysis, in which a reduced output that corresponds to the visible state of the simulation is rendered in-situ and stored to disk. These techniques can support interactive exploration of the data through image compositing and other methods, but automatic methods of highlighting data and reducing clutter can make these methods more effective. In this paper, we suggest a method of assisted exploration through
the combination of feature-centric analysis with image space techniques and show how the reduction of the data to features of interest reduces occlusion in the output for a set of example applications
The reduction of plankton biomass induced by mesoscale stirring: a modeling study in the Benguela upwelling
Recent studies, both based on remote sensed data and coupled models, showed a
reduction of biological productivity due to vigorous horizontal stirring in
upwelling areas. In order to better understand this phenomenon, we consider a
system of oceanic flow from the Benguela area coupled with a simple
biogeochemical model of Nutrient-Phyto-Zooplankton (NPZ) type. For the flow
three different surface velocity fields are considered: one derived from
satellite altimetry data, and the other two from a regional numerical model at
two different spatial resolutions. We compute horizontal particle dispersion in
terms of Lyapunov Exponents, and analyzed their correlations with phytoplankton
concentrations. Our modelling approach confirms that in the south Benguela
there is a reduction of biological activity when stirring is increased.
Two-dimensional offshore advection and latitudinal difference in Primary
Production, also mediated by the flow, seem to be the dominant processes
involved. We estimate that mesoscale processes are responsible for 30 to 50% of
the offshore fluxes of biological tracers. In the northern area, other factors
not taken into account in our simulation are influencing the ecosystem. We
suggest explanations for these results in the context of studies performed in
other eastern boundary upwelling areas
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