13,586 research outputs found
Numerical studies of the scattering of light from a two-dimensional randomly rough interface between two dielectric media
The scattering of polarized light incident from one dielectric medium on its
two-dimensional randomly rough interface with a second dielectric medium is
studied. A reduced Rayleigh equation for the scattering amplitudes is derived
for the case where p- or s-polarized light is incident on this interface, with
no assumptions being made regarding the dielectric functions of the media.
Rigorous, purely numerical, nonperturbative solutions of this equation are
obtained. They are used to calculate the reflectivity and reflectance of the
interface, the mean differential reflection coefficient, and the full angular
distribution of the intensity of the scattered light. These results are
obtained for both the case where the medium of incidence is the optically less
dense medium, and in the case where it is the optically more dense medium.
Optical analogues of the Yoneda peaks observed in the scattering of x-rays from
metal surfaces are present in the results obtained in the latter case. Brewster
scattering angles for diffuse scattering are investigated, reminiscent of the
Brewster angle for flat-interface reflection, but strongly dependent on the
angle of incidence. When the contribution from the transmitted field is added
to that from the scattered field it is found that the results of these
calculations satisfy unitarity with an error smaller than .Comment: 25 pages, 14 figure
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
The Design of Random Surfaces with Specified Scattering Properties: Surfaces that Suppress Leakage
We present a method for generating a one-dimensional random metal surface of
finite length L that suppresses leakage, i.e. the roughness-induced conversion
of a surface plasmon polariton propagating on it into volume electromagnetic
waves in the vacuum above the surface. Perturbative and numerical simulation
calculations carried out for surfaces generated in this way show that they
indeed suppress leakage.Comment: Revtex 6 pages (including 4 figures
GPR clutter amplitude processing to detect shallow geological targets
The analysis of clutter in A-scans produced by energy randomly scattered in some specific geological structures, provides information about changes in the shallow sedimentary geology. The A-scans are composed by the coherent energy received from reflections on electromagnetic discontinuities and the incoherent waves from the scattering in small heterogeneities. The reflected waves are attenuated as consequence of absorption, geometrical spreading and losses due to reflections and scattering. Therefore, the amplitude of those waves diminishes and at certain two-way travel times becomes on the same magnitude as the background noise in the radargram, mainly produced by the scattering. The amplitude of the mean background noise is higher when the dispersion of the energy increases. Then, the mean amplitude measured in a properly selected time window is a measurement of the amount of the scattered energy and, therefore, a measurement of the increase of scatterers in the ground. This paper presents a simple processing that allows determining the Mean Amplitude of Incoherent Energy (MAEI) for each A-scan, which is represented in front of the position of the trace. This procedure is tested in a field study, in a city built on a sedimentary basin. The basin is crossed by a large number of hidden subterranean streams and paleochannels. The sedimentary structures due to alluvial deposits produce an amount of the random backscattering of the energy that is measured in a time window. The results are compared along the entire radar line, allowing the location of streams and paleochannels. Numerical models were also used in order to compare the synthetic traces with the field radargrams and to test the proposed processing methodology. The results underscore the amount of the MAEI over the streams and also the existence of a surrounding zone where the amplitude is increasing from the average value to the maximum obtained over the structure. Simulations show that this zone does not correspond to any particular geological change but is consequence of the path of the antenna that receives the scattered energy before arriving to the alluvial depositsPeer ReviewedPostprint (published version
Scattering Models and Basic Experiments in the Microwave Regime
The objectives of research over the next three years are: (1) to develop a randomly rough surface scattering model which is applicable over the entire frequency band; (2) to develop a computer simulation method and algorithm to simulate scattering from known randomly rough surfaces, Z(x,y); (3) to design and perform laboratory experiments to study geometric and physical target parameters of an inhomogeneous layer; (4) to develop scattering models for an inhomogeneous layer which accounts for near field interaction and multiple scattering in both the coherent and the incoherent scattering components; and (5) a comparison between theoretical models and measurements or numerical simulation
Computation of Electromagnetic Fields Scattered From Objects With Uncertain Shapes Using Multilevel Monte Carlo Method
Computational tools for characterizing electromagnetic scattering from
objects with uncertain shapes are needed in various applications ranging from
remote sensing at microwave frequencies to Raman spectroscopy at optical
frequencies. Often, such computational tools use the Monte Carlo (MC) method to
sample a parametric space describing geometric uncertainties. For each sample,
which corresponds to a realization of the geometry, a deterministic
electromagnetic solver computes the scattered fields. However, for an accurate
statistical characterization the number of MC samples has to be large. In this
work, to address this challenge, the continuation multilevel Monte Carlo
(CMLMC) method is used together with a surface integral equation solver. The
CMLMC method optimally balances statistical errors due to sampling of the
parametric space, and numerical errors due to the discretization of the
geometry using a hierarchy of discretizations, from coarse to fine. The number
of realizations of finer discretizations can be kept low, with most samples
computed on coarser discretizations to minimize computational cost.
Consequently, the total execution time is significantly reduced, in comparison
to the standard MC scheme.Comment: 25 pages, 10 Figure
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