The Experts below are selected from a list of 19581 Experts worldwide ranked by ideXlab platform
Siegfried Boseck - One of the best experts on this subject based on the ideXlab platform.
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scanning acoustic microscopy and its applications to material characterization
Reviews of Modern Physics, 1995Co-Authors: Siegfried BoseckAbstract:The scanning acoustic microscope is a powerful new tool for the study of the physical properties of materials and has been successfully used for imaging interior structures and for nondestructive evaluation in materials science and biology. Its principles of operation, resolution, penetration ability, and contrast mechanisms are simply described in this paper. Recent progress in the application of acoustic microscopy to material characterization in solid materials is summarized. The experimental elastic microanalysis of bulk materials is carried out by measuring $V(z)$, which includes examining the Reflectance Function of solid material, measuring the phase velocity and attenuation of leaky surface acoustic waves at the liquid-specimen boundary, and determining the elastic constants of the material. The layer thickness and mechanical properties of layered solids are studied by examining the dispersion properties of surface acoustic waves. A knowledge of the propagation properties of acoustic waves on the surface of materials is essential for understanding the contrast mechanisms and quantitative measurements in acoustic microscopy; these propagation properties are thus also briefly described in this paper. Finally, further developments of the scanning acoustic microscope aimed at improving its performance for quantitative evaluation are presented. These could expand the scope of the acoustic microscope as a diagnostic tool in many areas of science and technology.
Andre Morel - One of the best experts on this subject based on the ideXlab platform.
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bidirectional Reflectance Function for oceanic waters with varying chlorophyll concentrations measurements versus predictions
Limnology and Oceanography, 2005Co-Authors: Kenneth J Voss, Andre MorelAbstract:The bidirectional Reflectance of the ocean is an important parameter in ocean color remote sensing. Model predictions for case-1 waters were compared with measurements over a large range of chlorophyll concentrations (0.1‐10 mg m 23 Chl, where Chl represents the sum of chlorophyll a and phaeophytin a), but with restricted solar zenith angles. We used the measured chlorophyll concentration and a model to predict the shape of the upwelling spectral radiance distribution. We found that the model predicted the radiance in the view direction, normalized by the nadir radiance, to within 7%. We also found that Q(Eu/Lu) was predicted within 7%. The upward radiance field within oceanic waters is not isotropic, especially near the surface, where it depends strongly on the sun’s position. The radiances in near-horizontal directions always exceed the nadir radiance, and the horizontal radiances toward the sun (dominated by forward scattering) are always greater than in the antisolar direction (back scattering). Notwithstanding that multiple scattering occurs within the medium and thus tends to homogenize the radiant field, the polar and azimuthal asymmetries persist throughout the upper layers of the ocean. The experimental evidence of this phenomenon dates back to the end of the 1950s and 1960s (Jerlov and Fukuda 1960; Tyler 1960; Sasaki et al. 1962); yet, the theoretical analysis and modeling of the upwelling light field has been undertaken more recently (Morel and Gentili 1991, 1993, 1996). The quantitative study of this anisotropy, essentially based on theory and computations, has been prompted by the implication of this phenomenon in the ocean color remote sensing problem, in so far as the radiance emerging from the ocean depends on the bidirectional structure of the upward radiance field just beneath the interface. With the development of new instrumentation (Voss 1989a; Voss and Chapin 1992), measurements of the radiance distribution at sea have been resumed after a long interruption (Voss 1989b; Voss et al. 2003). The anisotropic character of the upward radiance field is conveniently expressed by the bidirectional Function, or QFunction (Austin 1974), by which any upward radiance L u is related to the planar upward irradiance Eu through
Shigeo Morishima - One of the best experts on this subject based on the ideXlab platform.
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curvature dependent Reflectance Function for rendering translucent materials
International Conference on Computer Graphics and Interactive Techniques, 2010Co-Authors: Hiroyuki Kubo, Yoshinori Dobashi, Shigeo MorishimaAbstract:Simulating sub-surface scattering is one of the most effective ways for realistically synthesizing translucent materials such as marble, milk and human skin. In previous work, the method developed by Jensen et al. [2002] significantly improved the speed of the simulation. However, the process is still not fast enough to produce realtime rendering. Thus, we have developed a curvature-dependent Reflectance Function (CDRF) which mimics the presence of a subsurface scattering effect.
James J Little - One of the best experts on this subject based on the ideXlab platform.
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Reflectance Function estimation and shape recovery from image sequence of a rotating object
International Conference on Computer Vision, 1995Co-Authors: James J LittleAbstract:We describe a technique for surface recovery of a rotating object illuminated under a collinear light source (where the light source lies on or near the optical axis). We show that the surface Reflectance Function can be directly estimated from the image sequence without any assumption on the Reflectance property of the object surface. From the image sequence, the 3D locations of some singular surface points are calculated and their brightness values are extracted for the estimation of the Reflectance Function. We also show that the surface can be recovered by using shading information in two images of the rotating object. Iteratively using the first-order Taylor series approximation and the estimated Reflectance Function, the depth and orientation of the surface can be recovered simultaneously. The experimental results on real image sequences of both matte and specular surfaces demonstrate that the technique is feasible and robust. >
Roberto Cipolla - One of the best experts on this subject based on the ideXlab platform.
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a single lobe photometric stereo approach for heterogeneous material
Siam Journal on Imaging Sciences, 2016Co-Authors: Roberto Mecca, Yvain Quéau, Fotios Logothetis, Roberto CipollaAbstract:Shape from shading with multiple light sources is an active research area, and a diverse range of approaches have been proposed in recent decades. However, devising a robust reconstruction technique still remains a challenging goal, as the image acquisition process is highly nonlinear. Recent Photometric Stereo variants rely on simplifying assumptions in order to make the problem solvable: light propagation is still commonly assumed to be uniform, and the Bidirectional Reflectance Distribution Function is assumed to be diffuse, with limited interest for specular materials. In this work, we introduce a well-posed formulation based on partial differential equations (PDEs) for a unified Reflectance Function that can model both diffuse and specular reflections. We base our derivation on ratio of images, which makes the model independent from photometric invariants and yields a well-posed differential problem based on a system of quasi-linear PDEs with discontinuous coefficients. In addition, we directly solve...