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| Titel |
Theoretical interpretation of light scattered by the surfaces of atmosphereless Solar-System bodies |
| VerfasserIn |
K. Muinonen, J. Tyynelä, O. Wilkman |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069781
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| Zusammenfassung |
| Two ubiquitous light-scattering phenomena are observed near opposition
for atmosphereless solar-system objects covered with regoliths:
negative linear polarization and nonlinear surge of brightness
(opposition effect). The phenomena are confined to
Sun-object-observer angles (phase angles) of less than 30 and 10
degrees, respectively. The coherent-backscattering and shadowing
mechanisms have been introduced to explain the phenomena sometimes
showing up at extremely small phase angles. Coherent backscattering
has been shown to contribute to both brightness and polarization,
whereas shadowing has been shown to contribute to the opposition
effect only.
We have uncovered a single-scattering interference mechanism, a
so-called interference dial, that can explain the considerable widths
of the observed negative polarization branches and that can
simultaneously contribute to the increase of brightness. The mechanism
is related to the internal electric fields of wavelength-scale
scatterers. First, a longitudinal internal-field component parallel to
the wave vector of the incident wave results in negative polarization
at intermediate phase angles with decreasing contribution towards the
backward and forward-scattering directions. Second, interference among
transverse internal-field components parallel to the incident electric
field vector gives rise to negative polarization near
backward-scattering directions, in resemblance to the
multiple-scattering mechanism of coherent backscattering. The
mechanism has been verified for both spherical and nonspherical single
scatterers with wavelength-scale sizes.
We present multiple-scattering modeling for atmosphereless
solar-system objects using the coherent-backscattering
radiative-transfer method.. In the novel modeling,
the fundamental scatterers in a regolith volume element are modeled
using size distributions of spherical scatterers. Using a photometric
model accounting for both coherent backscattering and shadowing due to
the porous medium with fractional-Brownian-motion roughness, we derive
constraints for the physical properties of the lunar surface. |
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