Robert M. Nelson, Bruce W. Hapke, Mark D. Boryta,

Ken S. Manatt, William D. Smythe, Desiree Kroner,

Adaeze Nebedum

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and Planetary I

Laboratory Simulations of Planetary Surfaces:

Understanding Regolith Physical Properties

from Astronomical Photometric Observations

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Galileo, 1636 Dialogues, p92

Salviati: “You must know then that

a given surface receives more or less

illumination from the same light

according as the rays of light fall

upon it less or more obliquely; the

greatest illumination occurs where the

rays are perpendicular”.

Simplicius: “Please explain further

for me, since I am not that quick

witted.”

The First Bi-directional Reflectance Measurements

Reflectance Phase Curve The Reflectance Opposition Effect

Δm

Phase Angle (deg)

Reflectance Phase Curve The Reflectance Opposition Effect

Δm

Phase Angle (deg)

Reflectance Phase Curve The Reflectance Opposition Effect

Δm

Phase Angle (deg)

Polarization Phase Curve The Polarization Opposition Effect

Umov, N (1905). "Chromatische depolarisation durch Lichtzerstreuung". Physik. Z. 6: 674–676 Lyot, B. (1929). Studies of the Polarization of Planets, NASA TT F-187. Lyot, B. 1929. Recherches sur la polarisation de la lumiere des planetes et de queldues substances terrestres. Ann. Obs. Meudon. 8, 1–161. Dollfus, A. (1975) Optical polarimetry of the Galilean satellites of Jupiter. Icarus, 25, pp. 416–435.

Polarization Phase Curve The Polarization Opposition Effect

Min

Crossover Point, a.k.a. Inversion Angle

Polarization Phase Curve The Polarization Opposition Effect

Min

Crossover Point, a.k.a. Inversion Angle

Slope

The Problem for Asteroids α≤30 deg

The Problem for Saturnian Satellites α≤7 deg

Schematic Representation of Shadow Hiding Opposition Effect (SHOE)

Hapke, B. W. 1963. A Theoretical photometric function for the lunar surface. J. Geophys. Res., 68, 4571-86.

Irvine, W. (1965). Multiple Scattering by Large Particles. Astrophys. J. 142, 1563-1575. Irvine, W. (1966). The Shadowing Effect in Diffuse Reflectance. G. Geophys. Res. 71, 2931-2937.

Schematic Representation of Coherent Backscattering Opposition Effect

Shkuratov, Yu. G. 1985. On the origin of the opposition effect and negative polarization for cosmic bodies with solid surface. In Astronomicheskii Circular 1400, pp. 3–6. Sternberg State Astron.

Inst., Moscow. [In Russian] Muinonen, K. 1990. Light Scattering by Inhomogeneous Media: Backward Enhancement and Reversal of Polarization. Ph.D. thesis, University of Helsinki. Hapke, B. 1990. Coherent backscatter and the radar characteristics of outer planet satellites. Icarus 88, 407–417. Mishchenko, M. I. 1992. The angular width of the coherent backscatter opposition effect: An application to icy outer planet satellites. Astrophys. Space Sci. 194, 327–333.

Coherent Backscattering vs. Shadow Hiding

If SHOE then most of the returned signal is singly scattered

If CBOE then most of the returned signal is multiply scattered

Sketch of optical path

Nelson et al, 1998, 2000,2002

Laboratory Approach: The Goniometric Photopolarimeter (GPP)

Nelson et al., 1998, 2000, 2002

0.056 < α < 5 deg

P.M.T.

Distinguishing CBOE from SHOE

GPP, 1998,2000,2002

Polarization Ratios

Expected behavior in LPR and CPR in returned signal

CPRLPR, AL203, 1.5 Microns (Nelson et al., 2000)

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Circular polarization ratio increases with

decreasing phase angle in high albedo

particulate materials

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

… consistent with Coherent Backscattering hypothesis

Nelson, R.M., et al., (2000).The Opposition Effect in Simulated Planetary Regoliths. Reflectance and Circular Polarization Ratio Change at Small Phase Angle. Icarus, 147, 545-558. Nelson, R. M. et al. (2002). Low phase angle laboratory studies of the opposition e%ect: search for Wavelengthdependence. Planetary and Space Science 50 (2002) 849 – 856

Circular polarization ratio increases with

decreasing phase angle in high albedo

particulate materials

Half Width Half Max vs. Particle Size

It is known theoretically (Stephen and Cwilich, 1986), and demonstrated experimentally in investigations of polystyrene spheres in liquid suspension (Van Abada et al., 1987) that : HWHM ~/2D

Where D is the diffusion length in the medium

D=~ (LsLa/3) 1/2

Ls is mean distance traveled between scatterings La is the mean distance traveled before absorption

However…

Mishchenko Predictions

Reflectance of 13 Al2O3 powders at 0.633 microns

Mischenko Model Compared to Al2O3 powders

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Most probable explanation:

Aluminum Oxide particles are not spherical

Rosenbush et al, 2014

The Challenge for Laboratory Investigators

0.056 < α < 5 deg Nelson et al., 1998,2000,2002

(P.M.T.)

The Old Configuration

Helmholtz Reciprocity Principle

Interchanging the light source and the detector in a bidirectional reflectance

measurement produces the physically identical configuration.

BDRF( i, e, θ)=BDRF(e, i, θ)

Helmholtz, 1859; Stokes, 1849, See Minnaert, 1941; Hapke, 2012, p 264-265

Helmholtz Reciprocity Principle

Interchanging the light source and the detector in a bidirectional reflectance

measurement produces the physically identical configuration.

BDRF( i, e, θ)=BDRF(e, i, θ)

Helmholtz, 1859; Stokes, 1849, See Minnaert, 1941; Hapke, 2012, p 264-265

“If I can see you, then you can see me” John W. Strutt, 1873

Helmholtz Reciprocity Principle

“If I can see you, then you can see me” John W. Strutt, 1873, (a.k.a. Lord Rayleigh!)

Interchanging the light source and the detector in a bidirectional reflectance

measurement produces the physically identical configuration.

BDRF( i, e, θ)=BDRF(e, i, θ)

Helmholtz, 1859; Stokes, 1849, See Minnaert, 1941; Hapke, 2012, p 264-265

Helmholtz configuration of goniometric photopolarimeter is an exact duplication of astronomical measurements.

The New Configuration

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Phase Curve Al2O3, 1.5 and 22.5 microns

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Phase Curve Al2O3, 1.5 and 22.5 microns

Data from 0.1 to 5 degrees are extrapolated to zero to determine peak

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Extrapolation done by two methods

1. Modified Surkatov-Akimov (y=a+b*x+c*exp(-d*x)) 2. New Mount San Antonio College Function (y=a*exp(b*x)+c*exp(d*x))

Akimov, L. A. 1980. Nature of the opposition effect. Vestn. Kharkov State University 204, 3–12.

Shkuratov, Yu. G. 1988. A diffraction mechanism for the formation of the opposition effect of the brightness of surfaces having a complex structure. Kinem.Fiz. Nebes. Tel. 4, 33–39.

Fit to lab data from 0.1 to 5 degrees

Phase Curve Maxima for 13 particle sizes, Al2O3

Particle Size (microns)

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Half Width Half Max vs. Particle Size It is known theoretically (Stephen and Cwilich, 1986), and

demonstrated experimentally in investigations of polystyrene spheres in liquid suspension (Van Abada et al., 1987) that :

HWHM ~/2D Where D is the diffusion length in the medium

D=~ (LsLa/3) 1/2

Ls is mean distance traveled between scatterings La is the mean distance traveled before absorption

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Not consistent with models (Mishchenko (1992) or Hapke (2013))

Mishchenko, M. I. 1992. The angular width of the coherent backscatter opposition effect: An application to icy outer Solar System satellites. Astrophys. Space Sci. 194, 327–333. Hapke, B.W. chapter 9, eq 9.24

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Models are premised on spherical particles.

Aluminum Oxide particles are not spherical.

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Models are premised on spherical particles.

Aluminum Oxide particles are not spherical.

Planetary Regolith Particles are also

not spherical.

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

What about Polarization Phase Curve?

Similar effects reported by Shkuratov et al., 2002, Fig14

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Preliminary Conclusions 1) Reflectance and Polarization Phase Curves depend on particle size

2) In highly reflective, highly porous media, the following also depend on particle size:

a) The location of the polarization minimum, b) The depth of the polarization minimum, c) The slope of the negative branch at the crossover point

3) When particle size is > ~ 2λ, the polarization phase curve is flat

4) It remains to be determined if these effects (2 and 3 above) apply to low albedo materials.

5) Both SHOE and CBOE reflectance mechanisms may have associated polarization phase curves.

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

1. If a reflectance phase curve and a polarization phase curve of solar system object can be obtained (even at a very small range of phase angles), it will soon be possible to determine (or at least constrain) important regolith properties.

2. Future missions to the Jovian system (particularly Europa) would derive great benefit from including polarization measurement capability.

Looking Ahead…

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Acknowledgements Dale P. Cruikshank Jay Gogeun Ludmilla Kolokolova Karri Muinonen Yuriy Shkuratov Ted Roush Nichoas Thomas Gorden Videen Robert A. West Yunzhao Wu

August 4, 2015 IAU 2015, FM 12: Dust and Ices II and

Planetary I

Al2O3, Ref@5 deg = 94.6 % SiC, Ref@5deg =22%

The Problem

Little shadow hiding expected in high albedo materials, but…