Light Scattering by Feldspar Particles: Modeling Laboratory
Measurements 1 Department of Physics, University of Helsinki,
Finland 2 Institute of Astronomy, Kharkov National University,
Ukraine 3 Finnish Geodetic Institute, Finland 4 Instituto de
Astrofsica de Andaluca, CSIC, Spain 5 Science Systems and
Applications, Inc., USA 6 US Army Research Laboratory, USA 7 Space
Science Institute, USA Evgenij Zubko 1,2, Karri Muinonen 1,3, Olga
Muoz 4, Timo Nousiainen 1, Yuriy Shkuratov 2, Wenbo Sun 5, and
Gorden Videen 6,7 Slide 2 Laboratory measurements of
single-scattering feldspar particles appear to be a huge challenge
for modeling Data adapted from Volten et al. 2001: JGR 106, pp.
1737517401 Slide 3 Data adapted from Dubovik et al. 2006: JGR 111,
D11208 Results of fitting feldspar at 0.442 m Slide 4 Data adapted
from Dubovik et al. 2006: JGR 111, D11208 Results of fitting
feldspar at 0.633 m Slide 5 from Dubovik et al. 2006: JGR 111,
D11208 Unfortunately, the parameters were different for the
different fits, and Simultaneous inversions of scattering matrices
measured at two wavelengths (0.442 m and 0.633 m) were not
successful in that a reasonably good fit was not achieved. The
root-mean-square (over all elements) fit for a single wavelength
was about 710%, while for two wavelengths the root-mean-square fit
did not drop below 20%. Little difficulties in modeling Slide 6
from Dubovik et al. 2006: JGR 111, D11208 Besides, the best fits
are obtained with a mixture of highly oblate and prolate spheroids.
However, the feldspar particles look highly irregular with aspect
ratio being somewhat about 1. Little difficulties in modeling Slide
7 Method: Discrete Dipole Approximation (DDA) Concept: Modeling
target with set of small sub-volumes Advantage: Arbitrary shape and
internal structure Modeling feldspar with agglomerated debris
particles Slide 8 More details in, e.g., Zubko et al. 2009: JQSRT
110, pp. 17411749 Modeling feldspar with agglomerated debris
particles Slide 9 Features of agglomerated debris particles: (1)
Highly irregular (2) Equi-dimensional (3) Fluffy (packing density
=0.236) Modeling feldspar with agglomerated debris particles Slide
10 Laboratory measurements of single-scattering feldspar particles
Refractive index m is estimated to be in range m = 1.51.6 +
0.0010.00001 i Data adapted from Volten et al., 2001 SEM image of
feldspar Size distribution is retrieved with the laser diffraction
method Slide 11 SEM image of feldspar Modeling laboratory
measurements of feldspar Refractive index: m = 1.5 + 0 i We
consider the range of particle radii r from 0.21 m through 2.25 m
at =0.442 m: x =332 at =0.633 m: x =2.122.3 Size distribution: r
2.9 For each size parameter x, we consider a minimum of 500 samples
of agglomerated debris particles in random orientations. This makes
our analysis being statistically reliable! Size parameter: x = 2 r/
Slide 12 Modeling laboratory measurements of feldspar at =0.442 m
Slide 13 Modeling laboratory measurements of feldspar at =0.633 m
Slide 14 We model light-scattering response measured in feldspar
particles at two wavelengths 0.442 and 0.633 m. We utilize model of
agglomerated debris particles and compute light scattering with the
discrete dipole approximation (DDA). Measurements can be
satisfactorily reproduced under realistic assumptions on size
distribution and refractive index of feldspar particles. Unlike
spheroidal model, agglomerated debris particles can fit
measurements at both wavelengths. Summary
