37,925 research outputs found
Practical Multiple Scattering for Rough Surfaces
Microfacet theory concisely models light transport over rough surfaces. Specular reflection is the result of single mirror reflections on each facet, while exact computation of multiple scattering is either neglected, or modeled using costly importance sampling techniques. Practical but accurate simulation of multiple scattering in microfacet theory thus remains an open challenge. In this work, we revisit the traditional V-groove cavity model and derive an analytical, cost-effective solution for multiple scattering in rough surfaces. Our kaleidoscopic model is made up of both real and virtual V-grooves, and allows us to calculate higher-order scattering in the microfacets in an analytical fashion. We then extend our model to include nonsymmetric grooves, allowing for additional degrees of freedom on the surface geometry, improving multiple reflections at grazing angles with backward compatibility to traditional normal distribution functions. We validate the accuracy of our model against ground-truth Monte Carlo simulations, and demonstrate its flexibility on anisotropic and textured materials. Our model is analytical, does not introduce significant cost and variance, can be seamless integrated in any rendering engine, preserves reciprocity and energy conservation, and is suitable for bidirectional methods
Quasi-specular reflection from particulate media
Specular reflection is known to play an important role in many fields of
scattering applications, e.g., in remote sensing, computer graphics,
optimization of visual appearance of industrial products. Usually it can be
assumed that the object has a solid surface and that the properties of the
surface will dictate the behavior of the specular component. In this study I
will show that media consisting of wavelength-sized particles can also have a
quasi-specular reflection in cases where there is ordered structure in the
media. I will also show that the quasi-specular reflection in particulate media
is more than just a surface effect, and planar particle arrangement below the
very surface can give arise to quasi-specular reflection. This study shows that
the quasi-specular reflection may contribute in some cases in the
backscattering direction, together with coherent backscattering and
shadow-hiding effects
Analytic height correlation function of rough surfaces derived from light scattering
We derive an analytic expression for the height correlation function of a
rough surface based on the inverse wave scattering method of Kirchhoff theory.
The expression directly relates the height correlation function to diffuse
scattered intensity along a linear path at fixed polar angle. We test the
solution by measuring the angular distribution of light scattered from rough
silicon surfaces, and comparing extracted height correlation functions to those
derived from atomic force microscopy (AFM). The results agree closely with AFM
over a wider range of roughness parameters than previous formulations of the
inverse scattering problem, while relying less on large-angle scatter data. Our
expression thus provides an accurate analytical equation for the height
correlation function of a wide range of surfaces based on measurements using a
simple, fast experimental procedure.Comment: 6 pages, 5 figures, 1 tabl
Light scattering from self-affine fractal silver surfaces with nanoscale cutoff: Far-field and near-field calculations
We study the light scattered from randomly rough, one-dimensional self-affine
fractal silver surfaces with nanoscale lower cutoff, illuminated by s- or
p-polarized Gaussian beams a few microns wide. By means of rigorous numerical
calculations based on the Green theorem integral equation formulation, we
obtain both the far- and near-field scattered intensities. The influence of
diminishing the fractal lower scale cutoff (from below a hundred, down to a few
nanometers) is analyzed in the case of both single realizations and ensemble
average magnitudes. For s polarization, variations are small in the far field,
being only significant in the higher spatial frequency components of evanescent
character in the near field. In the case of p polarization, however, the
nanoscale cutoff has remarkable effects stemming from the roughness-induced
excitation of surface-plasmon polaritons. In the far field, the effect is
noticed both in the speckle pattern variation and in the decrease of the total
reflected energy upon ensemble averaging, due to increased absorption. In the
near field, more efficient excitation of localized optical modes is achieved
with smaller cutoff, which in turn leads to huge surface electric field
enhancements.Comment: REVTeX 4, 10 page
Numerical simulation of electromagnetic wave scattering from planar dielectric films deposited on rough perfectly conducting substrates
Electromagnetic wave scattering from planar dielectric films deposited on
one-dimensional, randomly rough, perfectly conducting substrates is studied by
numerical simulations for both p- and s-polarization. The reduced Rayleigh
equation, which is the integral equation satisfied by the scattering amplitude
after eliminating the fields inside the film, is the starting point for the
simulation. This equation is solved numerically by considering a random surface
of finite length, and by introducing wave number cut-offs in the evanescent
part of the spectrum. Upon discretization, a system of linear equations is
obtained, and by solving this matrix system for an ensemble of surface
realizations, the contribution to the mean differential reflection coefficient
from the incoherently scattered field, (\nu=p,s), is obtained nonperturbatively. It is demonstrated
that when the scattering geometry supports at least two guided waves,
, has, in addition to the well known
enhanced backscattering peak, well-defined satellite peaks in agreement with
theory, for most of the parameters considered.Comment: 11 pages and 11 figure
Evaluation of the present theoretical basis for determination of planetary surface properties by earth-based radar
Spaceflight programs such as the planned Viking landing on Mars require the determination of planetary surface slopes and surface dielectric constants by earth-based methods. Heavy reliance is often placed on radar backscattering data for estimation of these surface properties. An assessment is presented of the basic theory by which the raw radar data are interpreted, and it is shown that serious difficulties and internal inconsistencies are present in the available theoretical formulas. The discussion brings into question the reliability of the presently available results for these surface properties as obtained by earth-based radar methods
Boundary scattering of phonons: specularity of a randomly rough surface in the small perturbation limit
Scattering of normally incident longitudinal and transverse acoustic waves by
a randomly rough surface of an elastically isotropic solid is analyzed within
the small perturbation approach. In the limiting case of a large correlation
length compared with the acoustic wavelength, the specularity reduction is
given by , where is the RMS roughness and is the
acoustic wavevector, which is in agreement with the well-known Kirchhoff
approximation result often referred to as Ziman's equation [J. M. Ziman,
Electrons and Phonons (Clarendon Press, Oxford, 1960)]. In the opposite
limiting case of a small correlation length, the specularity reduction is found
to be proportional to , with the fourth power dependence on
frequency as in Rayleigh scattering. Numerical calculations for a Gaussian
autocorrelation function of surface roughness connect these limiting cases and
reveal a maximum of diffuse scattering at an intermediate value of . This
maximum becomes increasingly pronounced for the incident longitudinal wave as
the Poisson's ratio of the medium approaches 1/2 as a result of increased
scattering into transverse and Rayleigh surface waves. The results indicate
that thermal transport models using Ziman's formula are likely to overestimate
the heat flux dissipation due to boundary scattering, whereas modeling
interface roughness as atomic disorder is likely to underestimate scattering
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