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Underlying Surface (underlying + surface)

Distribution by Scientific Domains

Earth and Environmental Science	60%

Selected Abstracts

Multi-scale Feature Extraction on Point-Sampled Surfaces

COMPUTER GRAPHICS FORUM, Issue 3 2003
Mark Pauly
We present a new technique for extracting line-type features on point-sampled geometry. Given an unstructuredpoint cloud as input, our method first applies principal component analysis on local neighborhoods toclassify points according to the likelihood that they belong to a feature. Using hysteresis thresholding, we thencompute a minimum spanning graph as an initial approximation of the feature lines. To smooth out the featureswhile maintaining a close connection to the underlying surface, we use an adaptation of active contour models.Central to our method is a multi-scale classification operator that allows feature analysis at multiplescales, using the size of the local neighborhoods as a discrete scale parameter. This significantly improves thereliability of the detection phase and makes our method more robust in the presence of noise. To illustrate theusefulness of our method, we have implemented a non-photorealistic point renderer to visualize point-sampledsurfaces as line drawings of their extracted feature curves. [source]

Monitoring and verifying cloud forecasts originating from operational numerical models

METEOROLOGICAL APPLICATIONS, Issue 3 2008
Christoph Zingerle
Abstract Weather satellites produce large amounts of observational data in real time. This information has high temporal and spatial resolution covering almost every region of the globe. The infrared (IR) window channels of operational meteorological satellites are sensitive to the clouds and to the underlying surface. Comparing the IR channel observations with synthetic satellite images is an effective way to evaluate the quality of cloud forecasts produced by numerical models. Assessment of potentially problematic features in the early stages of the forecast is essential in not only nowcasting and very short-range forecasting but also in a reliability check of a given numerical weather prediction model (NWP). A pre-operational real-time monitoring system is set up in the Finnish Meteorological Institute, using the observed and synthetic satellite images, and applying an entity-based verification method. Copyright © 2008 Royal Meteorological Society [source]

Hyperspectral retrieval of land surface emissivities using ARIES

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 645 2009
Jean-Claude Thelen
Abstract Here we demonstrate the feasibility of applying a fast radiative transfer code, based on empirical orthogonal functions, in conjunction with a 1D-Var physical retrieval system to hyperspectral data taken from space/airborne radiance measurements in order to retrieve the emissivity spectra of the underlying surface. This approach was successfully tested using hyperspectral data obtained during the JAIVEx campaign in 2007 with the Airborne Research Interferometer Evaluation System (ARIES) on board of the UK Atmospheric Research aircraft. Using ARIES has the advantage that, during low-level flights, the surface emissivities can be derived directly from the hyperspectral data. Thus ARIES is capable of providing both the hyperspectral radiance data and the ,true' surface emissivity which has obvious advantages for validating the retrieval of the surface emissivity spectra. © Crown Copyright 2009. Published by John Wiley & Sons, Ltd. [source]

Gauged harmonic maps, Born-Infeld electromagnetism, and magnetic vortices

COMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 11 2003
Fanghua Lin
We study maps from a 2-surface into the standard 2-sphere coupled with Born-Infeld geometric electromagnetism through an Abelian gauge field. Such a formalism extends the classical harmonic map model, known as the ,-model, governing the spin vector orientation in a ferromagnet allows us to obtain the coexistence of vortices and antivortices characterized by opposite, self-excited, magnetic flux lines. We show that the Born-Infeld free parameter may be used to achieve arbitrarily high local concentration of magnetic flux lines that the total minimum energy is an additive function of these quantized flux lines realized as the numbers of vortices antivortices. In the case where the underlying surface, or the domain, is compact, we obtain a necessary sufficient condition for the existence of a unique solution representing a prescribed distribution of vortices antivortices. In the case where the domain is the full plane, we prove the existence of a unique solution representing an arbitrary distribution of vortices and antivortices. Furthermore, we also consider the Einstein gravitation induced by these vortices, known as cosmic strings, establish the existence of a solution representing a prescribed distribution of cosmic strings cosmic antistrings under a necessary sufficient condition that makes the underlying surface a complete surface with respect to the induced gravitational metric. © 2003 Wiley Periodicals, Inc. [source]

Effects of different terrain on velocity standard deviations

ATMOSPHERIC SCIENCE LETTERS, Issue 1-4 2001
M. H. Al-Jiboori
Abstract The standard deviations of wind velocity components are calculated and compared based on the measurements of turbulence fluctuations over three underlying surfaces: uniform, inhomogeneous and urban. Statistical analysis shows that there are the differences between them which prove the influences of surfaces roughness on turbulence. Copyright © 2003 Royal Meteorological Society. [source]