coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system...
TRANSCRIPT
![Page 1: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/1.jpg)
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. MishchenkoNASA Goddard Institute for Space Studies, New York, USA
![Page 2: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/2.jpg)
Opposition effects for some solar system bodies
![Page 3: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/3.jpg)
![Page 4: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/4.jpg)
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).
![Page 5: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/5.jpg)
Main characteristics of the coherent back- scattering peak
HWHM = ,2 tr
.4
3)cos1(
3
1
eff
scatr r
fC
.diffuse
coherentdiffuse
diffuse
total
I
II
I
I
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.
![Page 6: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/6.jpg)
Scattering by a spherical volume randomly filled with small spheres
inc
inc
inc
inc
sca
sca
sca
sca
V
U
Q
I
ab
ba
ab
ba
V
U
Q
I
)()(00
)()(00
00)()(
00)()(
42
23
21
11
)(
)()(
1
1
a
bP
![Page 7: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/7.jpg)
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)
![Page 8: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/8.jpg)
Brightness and polarization opposition effects
m = 1.31, kR = 40, kr = 2
(Dlugach, Mishchenko, Liu, Mackowski 2011)
![Page 9: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/9.jpg)
Opposition effects for Saturn’s rings and Europa
Franklin and Cook 1965
Thompson and Lockwood 1992 Mishchenko et al. 2009
Franklin and Cook 1965Lyot 1929
![Page 10: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/10.jpg)
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.
![Page 11: Coherent backscattering and opposition phenomena exhibited by some atmosphere- less solar system bodies Janna M. Dlugach Main Astronomical Observatory](https://reader035.vdocuments.mx/reader035/viewer/2022062423/56649ed05503460f94bdeafb/html5/thumbnails/11.jpg)
Acknowledgments
Thank 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.