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Coherent backscattering and opposition phenomena exhibited Coherent backscattering and opposition phenomena exhibited

Coherent backscattering and opposition phenomena exhibited - PowerPoint Presentation

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Coherent backscattering and opposition phenomena exhibited - PPT Presentation

less solar system bodies Janna M Dlugach Main Astronomical Observatory of the National Academy of Sciences of Ukraine Kyiv Ukraine Michael I Mishchenko NASA Goddard Institute for Space Studies New York USA ID: 277731

mishchenko opposition effects angular opposition mishchenko angular effects backscattering coherent polarization nasa sciences profiles solar system consistent composed ukraine

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Slide1

Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies

Janna M. DlugachMain Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine

Michael I. Mishchenko

NASA Goddard Institute for Space Studies, New York, USASlide2

Opposition effects for some solar system bodiesSlide3
Slide4

Angular profiles of the enhancement factor and the degree of linear polarization

Angular profiles of the enhancement factor (dotted curves) and the degree of linear polarization (solid curve) for a semi-infinite homogeneous medium composed of sparsely distributed non absorbing Rayleigh scatters, illuminated by normally incident unpolarized light (Mishchenko et al., 2000

)

.Slide5

Main characteristics of the coherent back- scattering peak

HWHM =

The angular widths of the

observed

backscattering intensity

peaks are consistent with the results of theoretical

computations for particle sizes of the

order of the wavelength, packing densities ranging

from several percent to approximately 40%, and particle

compositions ranging from water ice (Europa,

Saturn’s rings) to silicates (44 Nysa and 64 Angelina).

The

observed

amplitudes of the peaks are consistent with

the theory of

coherent backscattering by a regolithic layer composed of submicrometer-sized grains.Slide6

Scattering by a spherical volume randomly filled with small spheresSlide7

Current numerical capability

Computational technique: the numerically exact superposition T-matrix method and the Fortran-90 multiple sphere T-matrix (MSTM) code developed for use on parallel computer clusters.http://www.eng.auburn.edu/users/dmckwski/scatcodes

N

= 1875,

m

= 1.31,

kR

= 31,

kr

= 2,

ρ

= 0.5

(Mackowski and Mishchenko 2011)Slide8

Brightness and polarization opposition effects

m

= 1.31,

kR

= 40,

kr

= 2

(Dlugach, Mishchenko, Liu, Mackowski 2011)Slide9

Opposition effects for Saturn’s rings and Europa

Franklin and Cook 1965

Thompson and Lockwood 1992

Mishchenko et al. 2009

Franklin and Cook 1965

Lyot 1929Slide10

Conclusion

The photometric and polarimetric observational data for several high-albedo solar system objects reveal coexisting brightness and polarization opposition effects of comparable angular widths and with angular profiles consistent with the exact solutions of the Maxwell equations. The results of our theoretical analysis point to the conclusion that both these effects are caused by the coherent backscattering of sunlight by regolithic layers composed of microscopic grains.Slide11

AcknowledgmentsThank you for your attention!

This research was partially sponsored by the NASA Radiation Sciences Program managed by Hal Maring and by the NASA Remote Sensing Theory Program managed by Lucia Tsaoussi.

We acknowledge support from the National Academy of Sciences of Ukraine under the Main Astronomical Observatory GRAPE/GPU/GRID Computer Cluster Project.