Understanding Regolith Physical Properties from Astronomical Photometric Observations

Transcription

1 Laboratory Simulations of Planetary Surfaces: Understanding Regolith Physical Properties from Astronomical Photometric Observations 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

2 The First Bi-directional Reflectance Measurements 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. August 4, 2015 IAU 2015, FM 12: Dust and Ices II and Planetary I

3 Reflectance Phase Curve The Reflectance Opposition Effect Δm Phase Angle (deg)

4 Reflectance Phase Curve The Reflectance Opposition Effect Δm Phase Angle (deg)

5 Reflectance Phase Curve The Reflectance Opposition Effect Δm Phase Angle (deg)

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

7 Polarization Phase Curve The Polarization Opposition Effect Min Crossover Point, a.k.a. Inversion Angle

8 Polarization Phase Curve The Polarization Opposition Effect Min Slope Crossover Point, a.k.a. Inversion Angle

9 The Problem for Asteroids α 30 deg

10 The Problem for Saturnian Satellites α 7 deg

11 Schematic Representation of Shadow Hiding Opposition Effect (SHOE) Hapke, B. W A Theoretical photometric function for the lunar surface. J. Geophys. Res., 68, Irvine, W. (1965). Multiple Scattering by Large Particles. Astrophys. J. 142, Irvine, W. (1966). The Shadowing Effect in Diffuse Reflectance. G. Geophys. Res. 71,

12 Schematic Representation of Coherent Backscattering Opposition Effect Shkuratov, Yu. G On the origin of the opposition effect and negative polarization for cosmic bodies with solid surface. In Astronomicheskii Circular 1400, pp Sternberg State Astron. Inst., Moscow. [In Russian] Muinonen, K Light Scattering by Inhomogeneous Media: Backward Enhancement and Reversal of Polarization. Ph.D. thesis, University of Helsinki. Hapke, B Coherent backscatter and the radar characteristics of outer planet satellites. Icarus 88, Mishchenko, M. I The angular width of the coherent backscatter opposition effect: An application to icy outer planet satellites. Astrophys. Space Sci. 194,

13 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

14 Laboratory Approach: The Goniometric Photopolarimeter (GPP) Nelson et al, 1998, 2000,2002 Sketch of optical path

15 Distinguishing CBOE from SHOE P.M.T < α < 5 deg Nelson et al., 1998, 2000, 2002

16 GPP, 1998,2000,2002

17 Polarization Ratios

18 Expected behavior in LPR and CPR in returned signal

19 CPRLPR, AL 2 0 3, 1.5 Microns (Nelson et al., 2000)

20 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

21 Circular polarization ratio increases with decreasing phase angle in high albedo particulate materials 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, 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) August 4, 2015 IAU 2015, FM 12: Dust and Ices II and Planetary I

22 However 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 ~ / 2 D Where D is the diffusion length in the medium D=~ (L s L a /3) 1/2 L s is mean distance traveled between scatterings L a is the mean distance traveled before absorption

23 Mishchenko Predictions

24 Reflectance of 13 Al2O3 powders at microns

25 Mischenko Model Compared to Al2O3 powders

26 Most probable explanation: Aluminum Oxide particles are not spherical August 4, 2015 IAU 2015, FM 12: Dust and Ices II and Planetary I

27 The Challenge for Laboratory Investigators Rosenbush et al, 2014

28 The Old Configuration (P.M.T.) < α < 5 deg Nelson et al., 1998,2000,2002

29 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

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

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

32 The New Configuration Helmholtz configuration of goniometric photopolarimeter is an exact duplication of astronomical measurements.

33 Phase Curve Al 2 O 3, 1.5 and 22.5 microns August 4, 2015 IAU 2015, FM 12: Dust and Ices II and Planetary I

34 Phase Curve Al 2 O 3, 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

35 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)) Phase Curve Maxima for 13 particle sizes, Al 2 O 3 Fit to lab data from 0.1 to 5 degrees Akimov, L. A Nature of the opposition effect. Vestn. Kharkov State University 204, Shkuratov, Yu. G A diffraction mechanism for the formation of the opposition effect of the brightness of surfaces having a complex structure. Kinem.Fiz. Nebes. Tel. 4, August 4, 2015 Particle Size (microns) IAU 2015, FM 12: Dust and Ices II and Planetary I

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

37 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 ~ / 2 D Where D is the diffusion length in the medium D=~ (L s L a /3) 1/2 L s is mean distance traveled between scatterings L a is the mean distance traveled before absorption

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

39 Not consistent with models (Mishchenko (1992) or Hapke (2013)) Mishchenko, M. I The angular width of the coherent backscatter opposition effect: An application to icy outer Solar System satellites. Astrophys. Space Sci. 194, Hapke, B.W. chapter 9, eq 9.24 August 4, 2015 IAU 2015, FM 12: Dust and Ices II and Planetary I

40 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

41 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

42 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

43 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

44 Looking Ahead 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. August 4, 2015 IAU 2015, FM 12: Dust and Ices II and Planetary I

45 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

46 The Problem Little shadow hiding expected in high albedo materials, but Al2O3, deg = 94.6 % SiC, Ref@5deg =22% August 4, 2015 IAU 2015, FM 12: Dust and Ices II and Planetary I