Skip this Video
Download Presentation
Umov effect for single-scattering agglomerate particles

Loading in 2 Seconds...

play fullscreen
1 / 16

Umov effect for single-scattering agglomerate particles - PowerPoint PPT Presentation

  • Uploaded on

Umov effect for single-scattering agglomerate particles. E. Zubko , 1,2 G. Videen, 3 Yu. Shkuratov, 2 K. Muinonen, 1,4 and T. Yamamoto 5. 1 Department of Physics, University of Helsinki, Finland 2 Institute of Astronomy, Kharkov National University, Ukraine

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' Umov effect for single-scattering agglomerate particles' - annice

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Umov effect for single-scattering agglomerate particles

E. Zubko,1,2 G. Videen,3 Yu. Shkuratov,2

K. Muinonen,1,4 and T. Yamamoto5

1 Department of Physics, University of Helsinki, Finland

2 Institute of Astronomy, Kharkov National University, Ukraine

3 Army Research Laboratory AMSRL-CI-EM, USA

4 Finnish Geodetic Institute, Finland

5 Institute of Low Temperature Science, Hokkaido University, Japan

May 8, 2012


Polarimetry of Comets

Dependence of polarization in comets on phase angle

Circumstances of polarimetric observations


Umov Effect

The brighter powder, the lower its linear polarization

N. Umov, Phys. Zeits. 6, 674-676 (1905)

Origin of the phenomenon –depolarization due to multiple scattering in regolith

N. Umov (1846-1915)

In 1960-1970, the qualitative law was quantified:

log(Pmax) linearly depends on log(A)


Umov Effect

Shkuratov & Opanasenko, Icarus 99, 468-484 (1992)


Umov Effect for Single-Scattering Particles

As was found in Zubko et al. (2011, Icarus, 212, 403– 415), the Umov effect holds also for single-scattering particles with size comparable to wavelength. Therefore, it can be applied to comets.

Geometric albedo A for single particles:


Here, S11(0) is the Mueller matrix element at back-scattering, k – wavenumber, and G – the geometric cross-section of the particle.


Numerical Simulation of Light Scattering

Method: Discrete Dipole Approximation (DDA)

Basic idea:

Gains:(1) arbitrary shape and internal structure (2) simplicity in preparation of sample particles


Models for Cometary Dust Particles

sparse agglomerate

agglomerated debris

pocked spheres

ρ = 0.169

ρ = 0.236

ρ = 0.336


Input Parameters for Simulation

We study 21 (!) variousrefractive indices m:

1.2+0i 1.2+0.015i1.313+0i1.313+0.1i

1.4+0i1.4+0.0175i 1.4+0.02i 1.4+0.05i 1.4+0.1i

1.5+0i1.5+0.02i 1.5+0.05i 1.5+0.1i

1.6+0.0005i 1.6+0.02i 1.6+0.05i 1.6+0.1i 1.6+0.15i


Size parameter x=2r/ (r– radius of circumscribing sphere and – wavelength) is variedfrom 1 throughout 26 – 40 (depending on m).


Averaging of light-scattering characteristics

(1) Over particle shapes:

For each pair of x and m, we consider minimum 500 particle shapes.

(2) Over particle size:

Size distribution is considered to be a power law r–a. The power index a is varied from 1 to 4.

Note: this range is well consistent with in situ study of Comet 1P/Halley: 1.5a3.4 (Mazets et al., 1986)


Application to innermost coma in 26P/Grigg-Skjellerup

McBride et al., MNRAS 289, 535-553 (1997)



Using the Umov effect, one can estimate albedo of single-scattering dust particles.

When this technique is applied to whole Comet C/1996 B2 (Hyakutake), it yields the geometric albedo in the range A=0.034–0.079, that is well consistent with the expected value of A=0.05.

For the innermost coma studied by Giotto in 26P/Grigg-Skjellerup, the Umov effect reveals dramatically higher geometric albedo A=0.23.